1.1 EXOPHTHALMOMETRY
Pallavi Singh, Siddhi Goel
INTRODUCTION
Disorders of the orbit are quite commonly seen in ophthalmic practice. These are often associated with displacement of the globe from its normal position in the orbit. Exophthalmometer is an instrument used for measuring the degree of displacement of the globe. It is used for measurement of both exophthalmos as well as enophthalmos.
PRINCIPLE
Exophthalmometry is the science of quantitatively assessing the position of the globe in the orbit, by measuring the distance of the anterior corneal apex from the lateral margins. There are three different types of clinical exophthalmometry:
- Absolute: Comparison with the normal values seen in the general population.
- Relative: Comparison of one eye with the other.
- Comparative: Comparison of measurements of one eye over a period.
TYPES OF EXOPHTHALMOMETER
Various types of exophthalmometer have been described over the years. The first such device, called ophthalmoprostatometer was developed by Cohn in 1865.1 Perpendicular globe position was obtained by Zehender, by placing a mirror medial to the cornea and parallel to his ruler. A sighting device was placed lateral to the ruler and exactly opposite to the marked center of the mirror, to ensure perpendicular position of the globe. The Hertel exophthalmometer was introduced in 1905 and till date remains, the most popular device used for clinical exophthalmometry. Luedde invented a pocket-sized device in 1938, which was an inexpensive and useful alternative to the previous devices. In 1970, Davanger sought to eliminate the error caused in measurement by parallax by introducing a prism, which moves forward and back. Naugle and Couvillion described their exophthalmometer in 1992, which uses superior and inferior orbital rims as reference points, thus enabling measurements in cases of lateral orbital wall fractures. Hertel's exophthalmometer has been variously modified to use the external auditory meatus as the point of reference (Yeatts) and with a fixation adapter to fixate on the forehead and nose (Kratky and Hurwitz). Computed tomography scans can be used to document the degree of proptosis accurately, however, 4they are expensive, time consuming and cause radiation exposure.1
TECHNIQUE
To use the Hertel's exophthalmometer, the examiner sits opposite the patient at eye level. The instrument is then placed at both the lateral orbital rims and the base distance between the two is noted. The examiner asks the patient to look straight ahead with eyelids wide open. Each eye is measured separately for proptosis by looking into the mirror (which has a millimeter scale marked on it) with one eye and moving the head side to side until the red fixation lines match up, thus eliminating any parallax. The examiner can now determine the position of the corneal apex of the patient from the millimeter reading.
NORMAL VALUES
The normal values in exophthalmometry are taken as 10–23 mm (average 16 mm) in whites, and 12–23 mm (average 18 mm) in blacks. On an average, in the Indian population, a value of greater than 21 mm or a difference of 2 mm or greater between two eyes is considered significant.2,3
VIVA QUESTIONS
1. What are the different types of exophthalmometry?
Ans. There are three different types of exophthalmometry:
- Absolute: Comparison with the normal values seen in the general population.
- Relative:
- Comparison of one eye with the other
- Normal values are ≤2 mm.
- Comparative:
- Serial exophthalmometry readings of the same eye are compared over time
- It is better to use the same instrument
- Useful in Graves’ disease
- Hertel preferred over Luedde.
2. Name different types of exophthalmometer.
Ans. Hertel, Naugle, Luedde, Zehender, Davanger, and Gormaz are a few different types of exophthalmometers.
Hertel's (Figs. 1.1.1 and 1.1.2)
- It has a Foot-plates (or yokes) “grooved arc” to fit over bony temporal margin of lateral orbital rim; a crossbar to establish baseline and to allow for binocular reading.
- It uses prisms (Marco's) or mirrors (B&L's or Lombart's) incline at 45° from sagittal plane.
- Overall dimensions are 25 × 7 × 2 cm. Weight is 117 g (4.1 oz)/light weight or 216 g (7.6 oz)/heavy duty.
- Scale for orbital wall goes from 75 mm to 121 mm.
- The scale to measure the proptosis ranges from 0 mm to 35 mm.
Luedde (Fig. 1.1.3)
- It is a transparent plastic mm ruler. It has a notch that conforms to angle of lateral orbital rim
- Scale readings: 0 mm (end of notch) to 40 mm
- Parallax is minimized by using scale on both sides of the rod (advantages of using Luedde over a standard ophthalmic millimeter ruler).
Naugle's Exophthalmometer (Fig. 1.1.4)
This is an inferior and superior rim-based instrument. It may be used when the lateral orbital rim is not intact.
3. What are the advantages of Hertel's exophthalmometer?
Ans. The advantages are:
- Binocular reading: It provides the ability to measure both eyes simultaneously and the measurement of the distance between lateral orbital rims.
- Baseline for sequential readings: It is also useful for serial follow-ups of the same patient.
- Best for comparative exophthalmometry.
4. What are the disadvantages of Hertel's exophthalmometer?
Ans. The disadvantages are:
- Parallax error while performing measurements—tilting of instrument leading to minor deviations in position result in gross variations in reading.
- Difficulty of visualizing the scale under conditions of low illumination, which may result in inaccurate readings.
- Variations in the distance between the two halves of the instruments lead to displacement of the footplate which considerably affects the measurement.
- It is also a relatively expensive instrument.
- Induced error may occur when measuring globes that are not horizontally at the same level.
- Narrow base on Hertel—difficult setting up.
- Facial bone deformity—may cause unreliable measurements due to unparalleled placement of device while measuring globes that are not horizontally at the same level.
- Poor fixation or convergence can lead to unreliable measurement.
5. What are the advantages of Luedde's exophthalmometer over Hertel's?
Ans. The advantages are:
- Luedde's exophthalmometer measures degree of proptosis of each eye separately, thus is useful in cases of facial asymmetry.
- It is pocket-sized, portable, and easily stored.
- It is easier to clean and sterilize.
- It is cheaper as compared to the Hertel's exophthalmometer.
- It can be used in presence of strabismus.
6. What are the advantages of Naugle's exophthalmometer over Hertel's?
Ans. Advantages are:
- It utilizes superior and inferior orbital rims for measurement, thus can be used in cases of lateral orbital rim fractures.
- It also has the advantage of measuring hyperophthalmos and hypo-ophthalmos with a vertical gradient scale.
7. What is the definition of exophthalmos/enophthalmos?
Ans. Exophthalmos is a protrusion of the eyeball due to an increase in orbital contents in a normal bony orbit. Protrusion of the eyeball more than 21 mm or a difference of 2 mm between both the eyes is defined as proptosis/exophthalmos. Enophthalmos is abnormal posterior displacement of globe (sinking of eyeball into orbit).
8. What are the causes of pseudoproptosis?
Ans. Causes are:
- Facial asymmetry
- Unilateral high myopia
- Buphthalmic eye
- Lid retraction
- Enophthalmos of the other eye.
9. What is exorbitism?
Ans. Exorbitism is a protrusion of the eyeball due to a decrease in capacity of the orbital container, with a normal orbital content volume, as seen in Crouzon's syndrome.
10. How is proptosis measured on CT scan?
Ans. The method described by Hilal and Trokel is most commonly used.4 In a mid-axial CT scan, a line is drawn connecting the tips of the orbital rims. The perpendicular distance from this line to each corneal apex is measured. Proptosis is present if either line measures greater than 21 mm or the difference between the two eyes is more than 2 mm.
11. What are clinical ways to assess exophthalmos?
Ans. The various examination techniques are:
- Worm's eye view: Looking at the patient from down below, when the head is tilted backward to look for protrusion of the eyeball.
- Naffziger's view: Looking at patient from above, with the head tilted backward, to look for eyeball protrusion. Alternatively, asking the patient to close eyes and then open them, with the head tilted backward, to see which cornea is seen first on eye opening.
- Ruler method: Placing a ruler parallel to the coronal plane, touching the superior and inferior orbital rims, and looking for the relative position of the corneal apex to the ruler.
12. What are the factors influencing exophthalmometry reading?
Ans. Several factors can influence exophthalmometry reading such as:3
- Age: Lower readings are recorded for children (average 14 mm). In children and teenagers mean exophthalmometric measurements increase with age.5
- <4 years old (13.2 mm)
- 5–8 years old (14.4 mm)
- 9–12 years old (15.2 mm)
- 13–17 years old (16.2 mm)
- Sex: Males have higher readings (~1 mm)
- Posture: In supine position normal eyes sink back 1–3 mm in Graves’ disease, eyes are not affected by this phenomena.
- Ethnicity: Blacks have higher reading. Asians have smaller ranges.
- Spherical equivalent: Negatively correlated.3
- Axial length: Positively correlated.3
REFERENCES
- Genders SW, Mourits DL, Jasem M, et al. Parallax-free Exophthalmometry: a comprehensive review of the literature on clinical Exophthalmometry and the introduction of the first parallax-free exophthalmometer. Orbit Amst Neth. 2015;34(1):23–9.
- Ramli N, Kala S, Samsudin A, et al. Proptosis—Correlation and Agreement between Hertel Exophthalmometry and Computed Tomography. Orbit Amst Neth. 2015;34(5):257–62.
- Hilal SK, Trokel SL. Computerized tomography of the orbit using thin sections. Semin Roentgenol. 1977;12(2):137–47.
- Dijkstal JM, Bothun ED, Harrison AR, et al. Normal Exophthalmometry measurements in a United States pediatric population. Ophthal Plast Reconstr Surg. 2012;28(1):54–6.
1.2 ORBITAL IMAGING TECHNIQUES
Sanjay Sharma, Savinay Kapur
ORBITAL RADIOGRAPHS
Standard projections for the bony orbit include posteroanterior (PA) (Fig. 1.2.1A), lateral (Fig. 1.2.1B), and optic foramen view (Fig. 1.2.1C). The patient can either be seated, standing or semiprone. The PA projection also called the occipitofrontal view is done with a 20° caudal tilt, with the central beam exiting at the nasion. On the radiographs, the innominate line (Fig. 1.2.1A, black arrows) should cross the greater wing of sphenoid on the temporal side of the orbit.
Figs. 1.2.1A to C: Different commonly done normal orbital radiographs views. (A) Anteroposterior (AP) view; (B) Lateral view; and (C) Optic foramen view (marked by a white arrow). Black arrows mark the innominate line.
8For the lateral view, the patient is positioned with the mid sagittal plane of the skull placed parallel to the image receptor. The beam is centered at a point 2.5 cm posterior to the outer canthus. To evaluate whether a radiograph is true lateral or not, look at the superimposition of the floor of the anterior cranial fossa on both sides. For visualizing the optic foramen, Rhese projection is used. Here the head is placed on the detector face first such that cheek, nose, and chin touch the detector, with orbit in center. The head is tilted in a manner such that the orbitomeatal line is perpendicular to the detector, keeping the mid sagittal plane at an angle of 53° to the image receptor. Beam is centered 2.5 cm superior and 2.5 cm posterior to the upper external auditory meatus. The superior orbital fissure and optic foramen are well seen on this view as are the margins of the orbit. With the increasing use of modern cross-sectional imaging this view is not commonly requested. The current use of orbital radiographs are limited to patients with trauma or suspected intraorbital foreign body. In many centers, it is now restricted only to exclude foreign body prior to a magnetic resonance imaging (MRI) examination.
ULTRASOUND
Nowadays, ultrasound is considered as an extension of physical examination due to its easy availability and noninvasive nature. It is the first line of investigation for evaluation of ocular and orbital pathology. Its main utility lies in evaluation of intraocular lesions, especially when the media is opaque. It also acts as a problem solving tool after computed tomography (CT)/MRI as it allows for differentiation of cystic from solid lesions. Also, being a dynamic modality, it can be used to assess intraorbital pathologies and extraocular muscles (EOMs) in various stages of contraction. However, an inherent limitation of ultrasound is the trade-off between image resolution and depth of evaluation. High frequency probes permit high resolution imaging, but allow only limited depth of evaluation. Hence, its utility for evaluation of deep seated orbital pathologies is limited. Both A (amplitude) and B (brightness) (Fig. 1.2.2A) mode scans are used. The A-mode scan is mainly used by ophthalmologists where spikes are produced by the returning echoes from different interfaces within the eye. B-mode scan of the eyeball is done with a linear high resolution array transducer with frequency between 7.5 MHz and 10 MHz. For evaluation of the orbit, a lower frequency probe with 5–7.5 MHz bandwidth is used. To maintain an air free interface, coupling gel is applied over closed eyelids. In a normal individual, the anterior and posterior chambers are cystic (no echoes seen within anechoic) with an echogenic lens present between the two. Posterior to the globe, echogenic fat (Fig. 1.2.2A) is seen with a central hypoechoic linear structure representing the optic nerve sheath complex (Fig. 1.2.2A).
Figs. 1.2.2A and B: (A) Normal orbital ultrasound; and (B) Doppler in a child with persistent hyperplastic primary vitreous (PHPV) showing embryonic vascular channel marked by a white arrow.
9A color Doppler evaluation may be done to evaluate the blood flow in suspected persistent hyperplastic primary vitreous (PHPV) (Fig. 1.2.2B, shown by a white arrow) tumors and vascular malformations. In vascular lesions such as arteriovenous malformation (AVMs) and caroticocavernous fistula, spectral trace can be obtained to confirm the arterial or venous nature of flow. This information has an important therapeutic implication. Another new tool which can add to the evaluation of intraocular masses is contrast-enhanced ultrasound. Microbubble-based ultrasound contrast agents stay within the intravascular compartment and hence differentiate masses from pseudomasses (like retinal detachment/hemorrhage) as well as can potentially help to characterize masses as these tend to have different contrast kinetics. Ultrasound elastography is a yet another tool that evaluates the elasticity of a tissue that may find applications in times to come. Ultrasound biomicroscopy (UBM) is another exciting application for the evaluation of anterior chamber. It uses a high more than 30 MHz transducer to produce high resolution two-dimensional grayscale images of the anterior chamber.
COMPUTED TOMOGRAPHY
Computed tomography is a main orbital imaging modality which utilizes X-rays to generate cross-sectional images (slices). This volumetric cross-sectional information is used by software techniques to provide multiplanar images [along axial (Fig. 1.2.3A)/coronal (Fig. 1.2.3B)/sagittal/curved planes] as well as volume rendered imaging (3D dataset, Fig. 1.2.3C).
Figs. 1.2.3A to C: Normal orbital computed tomography (CT) sections; (A) Axial; and (B) Coronal; (C) A 3D volume rendered view in an adult with left tripod fracture.
CT scanning is based on the following principles:
- The images are acquired by a 360° rapid rotation of the X-ray tube around the patient. In modern CT scanners, the table moves horizontally through the gantry which houses the X-ray source and the detectors to generate helical (spiral) dataset.
- Hence, each point in the body is imaged by a number of X-ray beams at different angles which allows for depth assessment (third dimension). The final image is reconstructed from multiple X-ray projections depending on the attenuation coefficients of the tissues through which beam passes.
- Filtered back projection is the most commonly used method by which attenuation data is converted to an image.
- The attenuation value of tissues is expressed on a scale named Hounsfield units (HU) with a range of 3,000 HU. Cortex of bones generally has an attenuation value of around +800 to +1,000 HU (white on the CT image), air has an attenuation value in the range of −800 to −1,000 HU (black on the CT image), muscles and soft tissues have an attenuation value of +40 to +80 HU while fat has an attenuation of −40 to −80 HU. Water is defined by having zero attenuation as a standard reference.
CONTRAST-ENHANCED COMPUTED TOMOGRAPHY IMAGING
Contrast-enhanced CT (CECT) imaging of the orbit and brain is obtained following intravenous injection of an iodinated contrast medium. Enhancement of various tissues following contrast administration depends on their blood flow and vascular permeability. Iso-osmolar iodinated contrast media like iohexol (Omnipaque) and iodixanol (Visipaque) are used routinely with iodine concentration between 300 mgI/mL and 350 mgI/mL. Orbital fat provides an intrinsic background contrast against which some orbital pathologies can be visualized without requiring a contrast medium.
Q. When to order a contrast-enhanced CT scan?
Ans. The following clinical situations require an additional injection of a contrast medium:
- Mass lesions: Benign/malignant tumors
- Vascular lesions: Caroticocavernous fistula (CT angiogram)/cavernous sinus pathology
- Inflammatory conditions: Optic neuritis, cysticercosis, panophthalmitis/orbital cellulitis, especially if suspecting an abscess.
Q. (More importantly) when to order a noncontrast enhanced CT scan?
Ans.
- Where the clinical indication is for detection and localization of foreign bodies or trauma where assessment of bony fractures/extraocular muscle entrapment is of primary concern.
- To differentiate between acute hemorrhage and mass lesions as both would be bright on contrast-enhanced images [blood is hyperdense on noncontrast computed tomography scan (NCCT), most mass lesions are not).
- As a complimentary tool for detection of calcification/bony destruction in masses already being evaluated by MRI.
- When there is a contraindication to iodinated contrast media—renal function derangement/known contrast allergy.
- Thyroid ophthalmopathy to evaluate anatomy of EOMs and crowding at orbital apex.
ACQUISITION AND INTERPRETATION OF COMPUTED TOMOGRAPHY
The first step in acquisition of CT scans is obtaining a scout image/scannogram/localizer. For orbital CT, a lateral scout view is obtained which is a low dose X-ray projection where there is no gantry rotation around 11the patient but taken with a fixed position of the X-ray source and detectors. The use of a scannogram is to plan the acquisition and specify the craniocaudal extent of the scan. Volumetric data is now obtained with overlap between slices of the helix so that 3D reconstruction can be obtained.
Contrast can be given hand injected or by a pressure injector. For routine CECT, a hand injection is a safer, cheaper, and acceptable technique. Generally 50 mL of contrast in adults (2 mL/kg for children) would suffice for most indications. However, in cases where CT angiogram is required a pressure injector must be used. Angiograms are arterial phase images to evaluate arterial anatomy/supply (like in suspected AVMs and sometimes caroticocavernous fistula).
On hard copy CT films, the scannogram is usually displayed as the first image on the CT film, preceding the series of axial images. The scout view not only gives an overview, but also allows confirmation of the fact that the entire region of interest has been included in the scanned area
MAGNETIC RESONANCE IMAGING
Principle
Hydrogen is the most abundant element in human body. It has unpaired protons in their nuclei and therefore behaves as tiny magnet. These protons precess about their axis and as a result have a very small associated magnetic field. However, as they precess in different directions and are randomly oriented inside the body, the net magnetization vector is nullified. However, it changes when the human body is placed in a strong external magnetic field. The protons inside the hydrogen atoms act like tiny dipoles and get aligned along the direction of magnetic field, being either parallel or antiparallel to the field (longitudinal magnetization). They also rotate around their axes following the strength of the magnetic field. When a radiofrequency pulse is applied, these tiny dipoles are tilted off the equilibrium and start to precess in phase with one another in a direction perpendicular to the axis of the main magnetic field (transverse magnetization). When external pulse is switched off, the longitudinal magnetization is regained with time (T1 relaxation). There is also a loss of the transverse magnetization (T2 relaxation). T1 and T2 relaxation times (time needed to regain 66% of longitudinal magnetization and lose 66% of transverse magnetization, respectively) depend upon the composition of the tissue and also the environment in which the tissue is situated. Hence, different magnetic resonance sequences can be designed to make use of this difference in T1 and T2 relaxation times to display difference in composition of different tissues. These sequences can have different T1 and T2 weighting to display contrast between tissues which have different T1 and T2 relaxation times.
Magnetic Resonance Imaging Contrast Media
Most commonly used compounds for contrast enhancement are gadolinium-based. These are also extracellular agents like CT contrast media and are distributed in the intravascular and interstitial tissues depending on the blood flow and permeability. They shorten the T1 relaxation times and hence are bright on T1-weighted (T1W) images. Because fat is also bright on T1W images it needs to be suppressed so that enhancement is not masked due to bright signal of fat. Hence, postcontrast images are generally fat suppressed.
When to Choose MRI over CT?
- To assess intracranial pathologies including cranial nerves and cavernous sinus pathologies
- To see intracranial extent/spread of extracranial pathologies like fungal sinusitis
- Children.
Basic Image Sequences in MRI
T1-weighted Images (Figs. 1.2.4A and 1.2.5A)
Tissues with shorter T1 relaxation times such as fat appear brighter than those with longer T1 relaxation times such as water, vitreous, and cerebrospinal fluid (CSF).
It is the best sequence for studying anatomy.
T2-weighted Images (Figs. 1.2.4B and 1.2.5B)
Tissues with longer T2-relaxation like water, vitreous, and CSF appear brighter than tissues with shorter T2-relaxation such as blood products.
Fluid Attenuation Inversion Recovery (Fig. 1.2.5C)
Signals from free fluid can be suppressed using the fluid attenuation inversion recovery (FLAIR) sequence. FLAIR is especially useful in demyelinating conditions where white matter hyperintensities on T2W images are better appreciated when the bright signal from the adjacent CSF in the ventricles is nulled.
Figs. 1.2.4A to C: Routine normal magnetic resonance imaging (MRI) sequences of orbit in axial plane. (A) T1-weighted; (B) T2-weighted fat suppressed; and (C) T1-weighted postcontrast images.
It is the best sequence for studying in brain pathology.
Fat-suppressed Images (Figs. 1.2.4B and C)
Bright signals from intraorbital fat can mask the signal and enhancing pathologies. This problem can be overcome by suppressing the signal of fat by unique fat suppression 13sequences. It is an ideal sequence for identifying intraorbital pathology along with postcontrast T1W images.
Postcontrast Images (Figs. 1.2.4C and 1.2.5D)
Gadolinium does not cross the blood–brain barrier (BBB) and hence does not cause enhancement in the brain when BBB is intact. When the BBB is disrupted, gadolinium diffuses into the interstitial spaces resulting in their enhancement.
Diffusion-weighted Images
Primary application of diffusion-weighted images (DWI) in the brain is to look for acute infarcts. When there is cytotoxic edema, the cells swell and there is a restriction of diffusion in the extracellular space. This is reflected as a bright signal on DWI and low signal on apparent diffusion coefficient (ADC) maps. Always look at ADC maps to differentiate true diffusion restriction from “T2 shine through” (T2 bright areas may appear bright on DWI images without having diffusion restriction, however these are bright on ADC images as well).
Susceptibility-weighted Images
Magnetic resonance imaging sequences can either be spin echo or gradient echo sequences.
Figs. 1.2.5A to D: Routine normal magnetic resonance imaging (MRI) sequences of brain in axial plane. (A) T1-weighted; (B) T2-weighted; (C) Fluid attenuation inversion recovery (FLAIR); and (D) T1-weighted postcontrast images.
The technique of gradient echo images is beyond the scope of this book. However, it is important to know the utility of these images (Table 1.2.1). Susceptibility-weighted images (SWIs) are very sensitive to local field inhomogeneities and hence are therefore best to look for calcification and deoxyhemoglobin (hemorrhage).
Standard brain protocol—routine sections are taken at 5 mm
Orbit protocol:
- Thin (3 mm sections) T2 axial
- Thin T1 axial
- Thin T2 fat saturation axial, coronal (oblique sagittal on the side of pathology)
- Thin T1 fat saturation postcontrast images in all three planes.
EMISSION COMPUTED TOMOGRAPHY
Emission computed tomography is a form of scintigraphy wherein a radioactive tracer substance is injected intravenously. The tracer substance acts as a source of radiation for imaging. However, the spatial resolution is lower compared to CT as well as MRI. With single-photon emission computed tomography (SPECT), the radionuclides emit gamma and X-rays, and the images are obtained using a rotating gamma camera. This technique allows detection of disturbances of BBB as well as abnormalities of cerebral blood flow. Positron emission tomography (PET) on the other hand utilizes a β+ emitting nuclide (11carbon and 18fluorine) and is based on the concept of positron annihilation. It is frequently employed when there is suspicion of a systemic disease coexisting with orbital disease.15
1.3 A PATTERN-BASED APPROACH TO RADIOLOGIC DIAGNOSIS IN OPHTHALMOLOGY: PART I
Sanjay Sharma, Savinay Kapur
Most orbital pathologies can be divided into six basic imaging patterns:
- Intraocular: Retinoblastoma (RB), melanoma, metastasis, and endophthalmitis.
- Intraconal: Cavernous malformation, venous varix, lymphoproliferative disease and metastasis, and venolymphatic malformation.
- Extraconal: Dermoid, lacrimal gland masses, bone lesions, venolymphatic malformation, schwannoma, hemangiopericytoma, capillary hemangioma, sinonasal masses with orbital extension, postseptal infection, and lymphoproliferative lesions (Subperiosteal space is separate from extraconal compartment).
- Optic nerve sheath complex (ONSC) lesions: Meningioma, glioma, sarcoidosis, optic neuritis, idiopathic orbital inflammation, and lymphoproliferative disease (These are intraconal lesions).
- Conal [extraocular muscle (EOM) enlargement of various etiologies): Thyroid-associated orbitopathy, idiopathic orbital inflammation, carotid cavernous fistula (CCF), sarcoidosis, lymphoproliferative disease and metastasis, myocysticercus, and traumatic contusion.
- Infiltrative diseases: Metastasis, idiopathic orbital inflammation, lymphoproliferative disease, cellulitis, sarcoidosis, plexiform neurofibroma, and rhabdomyosarcoma.
Pearl:
- Three most common intraorbital pathologies—thyroid orbitopathy, lymphoproliferative disorders, and idiopathic orbital inflammation.
- Three most common transcompartmental orbital lesions—idiopathic orbital inflammation, capillary hemangioma, and venolymphatic malformation.
INTRACONAL LESIONS
Cavernous Hemangioma (A Slow Flow Venous Malformation)
Typical presentation: Painless, progressive proptosis in a middle-aged woman.
Imaging findings: They appear as well-defined (pathologically encapsulated), oval to round, and homogeneous masses with a density somewhat greater than that of the muscle. They are typically located within the intraconal space (especially laterally), but larger lesions may extend outside the muscle cone. Bone remodeling is seen with large and longstanding lesions. Small foci of calcification are sometimes present which represent phleboliths. Enhancement is generally moderate owing to the low vascular flow. The lesion enhances progressively with homogeneous enhancement on delayed images (Fig. 1.3.1). On magnetic resonance imaging (MRI), the lesion is hypointense on T1, hyperintense on T2-weighted images (T2WIs). Intralesional hemorrhage is uncommon (cf. cerebral cavernous malformation and lymphatic malformation).
Lymphangioma (Venolymphatic Malformation)
Typical presentation: Gradual, painless progressive proptosis in a child, often painful when sudden in onset.16
Fig. 1.3.1: Oblique parasagittal T1-weighted (T1W) fat suppressed postcontrast magnetic resonance imaging (MRI), with cavernous hemangioma, showing an ovoid enhancing soft tissue intraconal mass separate from the optic nerve.
Imaging findings: They appear as irregular heterogeneous masses, which are poorly defined (pathologically unencapsulated) and insinuate along normal orbital structures. They are known to cross anatomic boundaries such as the orbital septum and fascial layers. They can be macrocystic or microcystic. The macrocystic variant has multiple low-density cystic areas while in the microcystic variants the cysts are too small (to be seen on imaging) and hence look like a soft tissue mass. There is mild or no contrast enhancement. The wall and septae may show patchy enhancement, typically less than capillary hemangioma. Larger lesions may cause bone remodeling with extension into preseptal or infratemporal fossa through the inferior orbital fissure. Magnetic resonance (MR) is the investigation of choice for evaluating the extent of lesion. Signal characteristics depend on the presence or absence of proteinaceous contents/blood products within the lesion. In the absence of these, the cystic areas are hypointense on T1 and hyperintense on T2. Blood-fluid levels are characteristically seen in the setting of recent intralesional hemorrhage (Fig. 1.3.2).
Fig. 1.3.2: Axial T1-weighted (T1W) fat suppressed postcontrast magnetic resonance imaging (MRI), with lymphangioma (synonyms. venolymphatic malformation) showing a transcompartmental ill circumscribed mass lesion with foci of hemorrhage and fluid–fluid levels.
Venous Varix
Typical presentation: Painless, progressive proptosis that increases on stooping forward/Valsalva.
Imaging findings: Orbital varix represents a form of hamartoma, with thin-walled distensible venous channels that communicate with the normal orbital venous vasculature. Ultrasound is a highly useful modality for their diagnosis as it allows for dynamic assessment. The dilated venous channels collapse in the upright posture or at rest, but on straining, the increased blood flow with dilation of channels becomes obvious. On computed tomography (CT) the varices appear as an irregular or smooth variably enhancing lesion located at the orbital apex, which significantly increases in size with straining. However, as the study requires dynamicity and straining CT and MRI are seldom used for diagnosis. Once it is thrombosed, patients may present with acute onset retro-orbital pain and proptosis. CT at this time shows no change on straining and absence of enhancement. The lesion may appear hyperdense on noncontrast computed tomography (NCCT) due to hemorrhagic contents. MRI done at this time will show a 17well-defined T1/T2 heterogeneously hyperintense lesion due to hemorrhagic contents.
Pearl
Orbital varices can be a difficult radiologic diagnosis (on CT/MRI), as the discrete venous channels are seldom visualized.
Lymphoproliferative Disease and Intraconal Metastasis
Difficult to differentiate from other intraconal masses. Need evidence of a primary elsewhere to make this diagnosis. Rapid increase in size may be a pointer. Systemic work is warranted.
EXTRACONAL LESIONS
Dermoid Cyst
Typical presentation: Child or young adult with a mass near the frontozygomatic/frontoethmoid suture often with globe dystopia.
Imaging findings: It typically appears as a round to oval, well-defined lesion, located in the anterior superotemporal orbit. It is almost always extraconal and has a cystic center with areas of fat within (Fig. 1.3.3). A fat–fluid level may be present. Denser foci within the lesion represent flecks of keratin and sebum. The cyst is surrounded by a thin rim of tissue that may be partially calcified. Adjacent bone commonly shows remodeling/sutural widening. Occasionally the cystic cavity extends into the temporal fossa or the intracranial space. Contrast administration may produce mild enhancement of cyst rim, but not its center. On MRI, the lesion tends to be heterogeneously hyperintense on T2WI and hypointense on T1WI, however, areas of T1 hyperintensity are seen within the mass which show signal dropout on fat suppressed images.
Fig. 1.3.3: Axial noncontrast computed tomography (CT), with right medial angular dermoid, showing a well-defined mass of fat attenuation.
Orbital Schwannoma
Typical presentation: Painless, progressive proptosis along with symptoms due to mass effect on surrounding structures. May be present acutely with painful proptosis in cases of hemorrhage into the lesion.
Imaging findings: They are typically extraconal though they can be intraconal or extraconal or both. Commonly involves the frontal branches of the ophthalmic division of the trigeminal nerve. Schwannomas have a heterogeneous T2 signal (Fig. 1.3.4) and variable patterns of enhancement with homogeneous or ring enhancement being most common.
Fig. 1.3.4: Axial T2-weighted (T2W) fat suppressed magnetic resonance imaging (MRI), with right intraorbital schwannoma showing an elongated extraconal heterogeneous well-defined mass lesion with foci of necrosis and hemorrhage.
Hemangiopericytoma (Solitary Fibrous Tumor of Orbit)
These appear as homogeneous to heterogeneous, rounded or elongated masses of moderate density in an extraconal location most commonly along the paranasal sinuses. The borders are smooth and well circumscribed, similar to cavernous hemangioma. Calcification may be seen in up to one-fourth of cases. Bone erosion is unusual, but some degree of cortical disruption is sometimes seen along with rare periosteal reaction. Following contrast administration, enhancement is moderate to mark. Dynamic CT may show prominent early enhancement with rapid washout. The MRI image shows a round to oval tumor with well-defined borders. On the T1WI, the signal is isointense to cortical gray matter and muscle, and hypointense to fat. On the T2WI, the lesion is hyperintense to fat. Low-intensity signal voids represent large vessels with rapid blood flow. Moderate, diffuse, and homogeneous enhancement is seen with gadolinium.
Capillary Hemangioma
Typical history: Cutaneous discoloration or leash of vessels on the lids, periocular soft tissues; present at birth during infancy, grows with the child say up to 5–7 years age, and disappear by 10 years.
Imaging findings: They appear as ill-defined to irregularly marginated, lobulated, infiltrating masses most commonly located anterior to the globe in the eyelid. They show moderate to marked contrast enhancement. Longstanding lesions in young children may cause expansion of bony orbital volume. Rarely occur as intraosseous lesions forming expansile masses with intact tables. In its proliferative phase, the mass shows intense and early enhancement (in arterial phase) with multiple flow voids on T1W/T2W images. However, in its involuting phase or if it does not involute completely, they tend to have heterogeneous high signal intensity on T1W and T2W (Fig. 1.3.5) with heterogeneous enhancement on contrast images.
Fig. 1.3.5: Axial T2-weighted (T2W) fat suppressed magnetic resonance imaging (MRI), with right orbital capillary hemangioma, showing an ill-defined transcompartmental mass with areas of flow void. It showed marked contrast enhancement (in another section not shown).
Rhabdomyosarcoma
These lesions appear as irregular, moderate to well-defined soft tissue masses, mostly occupying the extraconal space, with about half extending into the intraconal space. Two-thirds of tumors arise in the superonasal quadrant of orbit. The density is similar to that of the EOMs, but may be heterogeneous due to intervening focal areas of hemorrhage. The tumor may conform to adjacent bony walls and orbital structures such as the globe. Bony erosion or destruction is unusual, but with larger lesions can be seen in up to 40% of cases. With contrast administration, 19mild to moderate uniform enhancement is observed.
Pearl
Most common malignancy of the orbit (head and neck region) in a child.
Lacrimal Gland Lesions
Benign neoplasms like pleomorphic adenoma present as indolent painless enlargement of the gland. Malignant and inflammatory lesions present with a shorter history and pain. They are broadly divided into epithelial and nonepithelial lesions. Epithelial lesions arise from the acini and tend to be neoplastic while nonepithelial lesions are predominantly inflammatory or infiltrative in nature. Adenoid cystic carcinoma is the most common malignancy of the lacrimal gland with propensity for perineural spread. CT scan of these lesions shows a heterogeneous mass in the lacrimal gland fossa area (Fig. 1.3.6). They can be irregular in shape with poorly demarcated margins or be round to oval in shape with well-defined borders. Larger tumors may extend along the lateral orbital wall to reach up to the orbital apex. Foci of calcification are frequently present within the lesion. Destruction or sclerosis of adjacent bone is a common phenomenon, especially with large tumors. Contrast administration shows areas of marked and focal enhancement.
Fig. 1.3.6: Axial contrast computed tomography (CT), with a left lacrimal gland mass (pleomorphic adenoma), showing heterogeneous enhancement, remodeling of the adjacent bone, and abaxial proptosis.
On MR, pleomorphic adenoma is typically isointense to muscle with bright enhancement. Lymphomas on the other hand have a homogeneous T2 hypointense signal higher than muscle. Lacrimal glands are the second most common location for idiopathic orbital inflammation.
Pearl
Idiopathic inflammatory inflammation and lymphomas are the two most common masses of lacrimal gland.
Bony Orbital Lesions
Orbital bone lesions are malignant or benign. Metastatic lesions are more common than primary malignancy. In children, the common causes are Ewing's and neuroblastoma (Fig. 1.3.7) while in adults metastases are common from lung, breast, and prostate.
Fig. 1.3.7: Axial computed tomography (CT) (bone window), in a 2-year-old child with metastatic neuroblastoma, showing a destructive left sphenoid bone lesion with spiculated periosteal reaction and abaxial proptosis.
20Meningiomas of the greater wing of sphenoid cause intraosseous growth, which may cause narrowing of intraorbital foramina. This sclerosis can be more easily seen on the CT images while on MR there is increase in the dark signal of the bone. Non-neoplastic benign fibro-osseous lesions include fibrous dysplasia (FD) and ossifying fibroma. FD is seen in patients less than 30 years of age. On CT, characteristic ground glass density is seen, with T1/T2 hypointensity on MR. Sagittal and oblique planes are helpful for evaluating the orbital apex and optic canal.
Mucocele
Longstanding lesions appear as masses opacifying one or more paranasal sinuses, extending into the orbit. The most common sinuses to get involved are frontal and ethmoid. The intervening bone may be expanded or remodeled or dehiscent around the cyst. This is best evaluated in bone window settings. Orbital structures are displaced, usually laterally or inferiorly. The cystic cavity is usually filled with a homogeneous, low-density mucoid material. The lesion lacks contrast enhancement unless contains pus. Longstanding inspissated secretions and proteinaceous contents appear T1 hyperintense and hyperdense on NCCT (Fig. 1.3.8) despite their cystic character.
INTRAOCULAR MASS
Metastases
In half of these cases, the intraocular metastases are asymptomatic, but in the other, they may present with vision loss or scotoma.
Fig. 1.3.8: Axial contrast computed tomography (CT), with right ethmoid mucocele, showing an expansile hyperattenuating lesion centered in the right anterior ethmoid sinus seen breaking into the orbit through the dehiscent lamina papyracea and causing abaxial proptosis.
Fig. 1.3.9: Axial T1-weighted (T1W) fat suppressed magnetic resonance imaging (MRI), with left intraocular metastatic lung cancer showing bright homogeneous enhancement and retinal detachment.
Uvea is the most common site for intraocular metastasis, mostly localized to the choroid. These tend to occur as flatter/broad based lesions (posterior to the equator) (Fig. 1.3.9), compared to melanoma which tend to mushroom shaped. The most common primary tumors responsible for intraocular metastases are lung for men and breast for women. The prevalence of orbital metastases ranges from 2% to 5%. Few tumors have a propensity to metastasize to particular tissues (prostate to bone, melanoma to EOMs, breast to fatty tissue, and EOMs). The overall 21distribution of orbital metastases is in a ratio of 2:2:1, bone:fat:muscle.
Retinal Detachment
Retinal detachment (RD) typically begins with posterior vitreous detachment and is typically a clinical diagnosis based on history and examination. On imaging, there is a characteristic V-shaped area of abnormal density in the posterior globe which is limited by the anterior attachment of the retina, in contradistinction to suprachoroidal collections, which extend anteriorly to the level of the ciliary body.
Pearl
Ultrasound is the best radiologic modality for its detection. A CT may completely miss the RD.
Uveal Melanoma
Uveal melanoma is the most common primary intraocular malignancy in adults, constituting 5–6% of melanoma diagnoses with up to 50% of patients developing distant metastases. It may arise in any part of the uvea, including the ciliary body, iris, or choroid (most common). Cross-sectional imaging is of use when ocular opacities limit assessment. MRI is the investigation of choice with characteristic findings of melanoma being marked hyperintensity on T1WIs and hypointensity on T2WIs (Figs. 1.3.10A and B) which makes this a unique tumor. It enhances brightly on contrast-enhanced CT and MR, however subtraction MR imaging may be needed to demonstrate enhancement as the tumor is bright on T1 images as well. MR is also useful for distinguishing the tumor from associated hemorrhage.
Pearl
Ultrasound should be the first-line radiologic modality for the evaluation of suspected intraocular masses, and MRI later, if required. Systemic workup is necessary for staging.
Retinoblastoma
Child typically presents with white reflex or strabismus. It is the most common intraocular malignancy in childhood. It is considered a clinical diagnosis supported by ultrasound.
Figs. 1.3.10A and B: Axial T1-weighted (T1W) (A) and T2-weighted (T2W) (B) fat suppressed magnetic resonance imaging (MRI), in an elderly man, with a polypoidal left intraocular mass, a uveal melanoma, which is bight on T1W and dark on T2W images.
22MRI is required for the larger tumors for local staging. Ultrasonography and MRI can both be useful to distinguish RB from other differential diagnoses, viz. Coats’ disease, persistent hyperplastic primary vitreous, retinopathy of prematurity (Fig. 1.3.11) or toxocariasis. CT is only considered a problem solving tool due to the radiation risk, CT is an excellent modality to detect small calcifications which may be diagnostic in doubtful cases (Fig. 1.3.12A). However, an A-mode ultrasound is a popular modality to evaluate calcification in the tumors. MRI is the preferred imaging modality for delineating the morphology and extent of the tumor, especially extraocular spread and optic nerve involvement (Fig. 1.3.12B). RB has characteristic low T2 signal, because of its high cellular density and variable postcontrast MR enhancement.
Pearl
Evaluation of white reflex in a child is a common and difficult clinical problem. The diagnosis is often not apparent even after thorough clinically evaluation and radiology.
Endophthalmitis
Endophthalmitis occurs either following surgery or trauma due to local inoculation or even secondary to hematogenous spread of infection from a distant anatomic site. Although usually a clinical diagnosis, the role of imaging remains detection of complications like formation of intraorbital abscess, RD, cavernous sinus involvement, and development of phthisis bulbi. The ocular coats are seen to be diffusely thickened (Fig. 1.3.13).
Fig. 1.3.11: Axial T2-weighted (T2W) magnetic resonance imaging (MRI), in a premature child who received oxygen in neonatal care for 2 weeks, having retinopathy of prematurity, showing bilateral microphthalmia, retinal detachment, and bilateral intraocular hemorrhage but no mass.
Figs. 1.3.12A and B: Axial noncontrast computed tomography (CT) (A) and T1-weighted (T1W) fat suppressed contrast-enhanced (CE) magnetic resonance imaging (MRI) (B) in another child with retinoblastoma, showing calcified right intraocular mass (A) and enhancing left intraocular mass with optic nerve involvement up to the apex.
Fig. 1.3.13: Axial contrast computed tomography (CT), with right metastatic endophthalmitis, showing diffuse thickening of right ocular coats but no fluid collection or abscess. An active abdominal sepsis was presumed to be the cause of his disease.
Abscesses can also occur in both the suprachoroidal space and the subretinal space. On CT and MR, abscesses are peripherally enhancing layers of predominantly fluid attenuation. On T2WI, the high signal of vitreous may obscure pathology; however, the inflamed uveal tract can be clearly seen separately from the vitreous on fluid-attenuated inversion recovery (FLAIR) imaging. Contrast MRI assisted may be useful in demonstrating abscesses.
1.4 A PATTERN-BASED APPROACH TO RADIOLOGIC DIAGNOSIS IN OPHTHALMOLOGY: PART II
Sanjay Sharma, Savinay Kapur
OPTIC NERVE SHEATH COMPLEX LESIONS
Optic Glioma
Typical presentation: Decreased visual activity, visual field defect, proptosis, and relative afferent pupillary defect (RAPD).
Imaging findings: These are glial tumors which in the brain arise from the parenchyma of white matter, but often also involve the adjacent gray matter. The Dodge classification divides these tumors into just three groups based on anatomical localization:
- Stage 1: Optic nerves only
- Stage 2: Chiasm involved (with or without optic nerve involvement)
- Stage 3: Hypothalamic involvement and/or other adjacent structures.
In patients of neurofibromatosis (NF), these lesions appear on computed tomography (CT) as hypodense and poorly-defined masses. The optic nerve cannot be seen separate from the mass; hence, the nerve appears tubular, tortuous, and kinked. Minimal or no enhancement is seen in the lesion. Sporadic gliomas tend to have solid cystic appearance similar to pilocytic astrocytomas. The solid areas are generally T2 hyperintense and show contrast enhancement (Fig. 1.4.1).
Pearls
If unilateral, NF1 in 20% patients; if bilateral— pathognomonic of NF1.
Optic Nerve Sheath Meningioma
Typical presentation: Insidious vision loss over months to years.
Fig. 1.4.1: Oblique sagittal T1-weight (T1W) postcontrast magnetic resonance imaging (MRI) of optic nerve glioma, showing a fusiform enhancing tumor not separate from the optic nerve.
Less commonly, they may be fusiform or globular in appearance in case the dura is breached. The lesion appears iso to hyperdense on CT and may show foci of calcification in 20–50% of cases. There is marked and homogeneous contrast enhancement of the mass, often with a linear central zone of reduced density representing the normal optic nerve (tram-tracking sign). Expansion of bony orbital walls is seen in case the tumor is longstanding. Meningiomas generally produce isointense signals on T1-weighted (T1W) images with respect to normal optic nerve and cortical gray matter. The T2-weighted (T2W) image is heterogeneous and varies from being slightly hypointense to slightly hyperintense (Fig. 1.4.2) with respect to the gray matter. The fibroblastic stromal elements give meningiomas their characteristic hypointense signal. The postgadolinium T1W image shows marked enhancement of the tumor surrounding an optic nerve of lower signal intensity with a dural tail. This is best distinguished on fat suppression sequences. A subtle intracranial extension may only be visible on the contrast image.
Pearl
Think of NF2, if multiple or associated with other neoplasms like schwannomas or ependymomas.
Fig. 1.4.2: Oblique sagittal T2-weight (T2W) magnetic resonance imaging (MRI) with optic sheath meningioma, showing a fusiform intermediate signal intensity neoplasm encasing the optic nerve. Note that the neoplasm is seen distinct from the optic nerve.
Optic Neuritis
Typical presentation: Unilateral rapid onset of vision loss; eye pain worsened with eye movements.
Imaging findings: Optic neuritis is a magnetic resonance imaging (MRI) diagnosis; CT has no role. Key imaging sequences—axial, coronal T2 FS, and T1 FS postcontrast are required. Optic nerve involvement may be segmental or diffuse. Optic neuritis manifests as increased T2 signal and bulk of the nerve which may be associated with abnormal enhancement.
Pearls
1st pearl: Always image the brain if optic neuritis presents as there is 25% risk of multiple sclerosis. Can also be seen with neuromyelitis optica (NMO).
2nd pearl: Hence screening of cervical spine with STIR sequence may be done.
3rd pearl: If bilateral (Fig. 1.4.3), then think of infectious causes, such as viral prodrome in children.
Idiopathic Orbital Inflammation
Typical presentation: Unilateral more common than bilateral, rapid onset pain + diplopia + vision loss and redness.25
Fig. 1.4.3: Axial postcontrast fat suppressed T1-weight (T1W) magnetic resonance imaging (MRI) with bilateral optic neuritis showing a marked enhancement of both optic nerves. Note that the normal optic nerves never enhance as brightly as the extraocular muscles (EOMs), as in this case.
Imaging findings: Orbital inflammation may be seen in a variety of orbital conditions, however, about 5–15% have no discernible cause and hence classified as idiopathic. Also called orbital pseudotumor, idiopathic orbital pseudotumor or nonspecific orbital inflammation. Many patients would have underlying systemic vasculitis as a cause. It may be related to immunoglobulin G4 (IgG4) disease. Here the optic nerve sheath is involved instead of the optic nerve itself. There is frequent involvement of retrobulbar fat, EOMs, lacrimal glands, and optic nerve. The masses are ill defined on CT. On MRI they are T1 intermediate, T2 dark, and show variable enhancement.
Radiological differential diagnosis—lymphoproliferative disease/sarcoidosis (neither has a similar clinical presentation), systemic vasculitis, and IgG4-related orbital disease.
Lymphoproliferative Disease
Includes lymphoma (most common), lymphoid hyperplasia and atypical lymphoid hyperplasia, and ocular adnexal lymphoma. Around a quarter of all masses in patients older than 60 years are lymphomas. Non-Hodgkin's lymphoma, specifically the mucosa-associated lymphoid tissue (MALT) form is the most common primary orbital lymphoma.
Sarcoidosis
Presentation is similar to inflammatory pseudotumor. Most common site of involvement is the uvea or lacrimal gland. On MRI, involvement of the optic nerve sheath may show linear tram-track enhancement. On imaging, if there is isolated optic nerve involvement, it may be indistinguishable from the above two conditions. Laboratory investigations [serum calcium and angiotensin-converting enzyme (ACE) levels] are supportive, besides the systemic workup for the evidence of the disease elsewhere in the body to help make the diagnosis.
CONAL (EXTRAOCULAR MUSCLE ENLARGEMENT)
Thyroid-associated Orbitopathy
Typical presentation: Bilateral painless axial proptosis.
Imaging findings: Most common extrathyroidal manifestation of Graves disease (25–50% patients). Caused by accumulation of glycosaminoglycans in the orbital soft tissues and increased fat volume. On CT, enlargement of EOMs is the imaging hallmark of the disease and is best appreciated on axial and coronal scans (Figs. 1.4.4A and B). The enlarged muscles are sharply defined, sometimes demonstrating increased density. There may be focal areas of low density, reflecting fatty infiltration. Typically, only the muscle bellies are involved, with relatively normal tendinous insertion referred to as 26the “coca-cola” sign seen on axial images (cf. pseudotumor). The inferior and the medial rectus muscles are the most frequently involved ones. The superior ophthalmic vein may be enlarged as a result of apical compression. The bulky EOMs are isointense on T1, slightly hyperintense on T2W images. The thickened tensor intermuscularis appears as a prominent curved band between the superior and lateral rectus muscles. Contrast administration is not necessary for imaging to make a diagnosis. Up to 8% of patients with thromboangiitis obliterans (TAO) develop dystrophic optic neuropathy (DON) likely secondary to optic nerve compression by the enlarged EOMs. The presentation may sometimes be asymmetric (unilateral) or even antedate the clinical disease.
Figs. 1.4.4A and B: Axial (A) and coronal (B) contrast-enhanced computed tomography (CECT) scan in thyroid-associated orbitopathy, shows bulky bellies of bilateral extraocular muscles (EOMs) especially inferior and medial recti. Note the typical tendinous sparing.
Idiopathic Orbital Inflammation
Typical presentation: Pain, ocular dysmotility, and redness.
Imaging findings: Myositis is one of the most common orbital manifestations of IOI. In contradistinction to TAO, IOI of the EOMs is typically unilateral, painful, and rapid in onset (hours to days). However, some patients may have an atypical presentation, with a relatively painless manifestation, or bilateral disease (25% of patients, common in children). On imaging, the differentiation is based on involvement of tendinous insertion with inflammation in the adjacent fat.
Carotid-cavernous Fistula
They have been variously classified by their hemodynamics (high or low flow), cause (spontaneous or posttraumatic), or vascular anatomy (direct or indirect) or vascular anatomy (direct or indirect, Table 1.4.1).
Computed tomography scan in these cases demonstrates proptosis with the prominence of the orbital vasculature. The superior ophthalmic vein is dilated in most cases. Low density, nonenhancing areas within the vessel or the cavernous sinus represent thrombosis. Symmetrical enlargement of EOMs from vascular engorgement is commonly seen.
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Fig. 1.4.5: Axial contrast-enhanced computed tomography (CECT) in a young male with carotico-cavernous fistula, showing engorged right superior ophthalmic vein. The swelling of left extraocular muscles is not seen in this section.
Enlargement of cavernous sinus may be appreciated, and in longstanding cases, the superior orbital fissure can be widened. Contrast CT is generally diagnostic in most cases (Fig. 1.4.5). However, invasive digital subtraction angiography (DSA) may be necessary some occasionally times, especially to demonstrate an indirect fistula or for interventional radiological treatment of CCF. On magnetic resonance (MR), vessels with fast flowing blood show a signal void on both T1W and T2W images and these can be demonstrated on gadolinium-enhanced magnetic resonance angiography (MRA) images.
Sarcoidosis
Involvement of the EOMs by sarcoidosis is unusual and can have a variety of presentations. There may be involvement of multiple muscles on one side or bilateral, painful or indolent, with or without involvement of other orbital soft tissues such as the lacrimal gland. It may spare or involve the tendinous insertions, and hence is difficult to differentiate from TAO or IOI by physical examination and imaging, especially if there is no evidence of systemic sarcoidosis.
Lymphoproliferative Disease and Metastases
Intramuscular metastases and lymphoma are rare. Metastases and lymphoma or other lymphoproliferative diseases occurring in the EOMs have been reported only sporadically in the literature. Carcinoma (predominantly breast), melanoma, non-Hodgkin lymphoma, and neuroendocrine tumors such as carcinoid are better known primaries. Breast carcinoma may sometimes involve the EOMs in a bilateral symmetric pattern with sparing of the tendons, which may be difficult to distinguish from TAO on imaging.
INFILTRATIVE DISEASES
Metastasis
Most common primary malignancy to metastasize to the orbits is breast carcinoma. Diffuse intraconal disease is one of many imaging patterns that may be seen in breast cancer, in addition to intramuscular or osseous masses. Infiltrative scirrhous breast carcinoma may cause enophthalmos, because fibrous tissue replaces the normal orbital fat.
Idiopathic Orbital Inflammation
Diffuse involvement of the orbital fat is less common than involvement of other orbital structures such as the lacrimal gland or EOMs (Fig. 1.4.6). The eponym “Tolosa–Hunt syndrome” applies when there is predominantly involvement of the orbital apex or cavernous sinus.
Lymphoproliferative Disease
Similar to IOI, lymphoproliferative disease such as lymphoma may present with an infiltrative pattern, involving any orbital structure. However, in contrast to IOI, lymphoproliferative disease presents with minimal or no pain and with gradual progression.28
Fig. 1.4.6: Axial contrast-enhanced computed tomography (CECT) in a middle-aged woman with idiopathic orbital inflammation, showing the infiltrating multicompartmental soft tissue mass involving left lateral rectus, lacrimal gland, retrobulbar fat, and preseptal soft tissues.
In some series, diffuse ill-defined orbital disease was found to be commoner than a well-circumscribed round or oblong mass. On MRI, T2W signal isointense or hypointense to muscle is typical of lymphoproliferative disease and restricted diffusion may also be seen.
Orbital Cellulitis
Involvement of the soft tissues posterior to the orbital septum is the imaging hallmark of orbital cellulitis (cf. preseptal cellulitis). It is important to make this distinction as orbital cellulitis has a higher complication rate and may be associated with optic neuropathy, encephalomeningitis, cavernous sinus thrombosis, sepsis, and intracranial abscess. Orbital cellulitis in early stages is characterized by eyelid edema and sinusitis on CT images. Postcontrast scans show marked increased in enhancement. More typically inflammation is seen in the medial or superomedial orbit adjacent to the opacified sinus, associated with fat stranding, i.e. heterogeneity in the retrobulbar fat (Fig. 1.4.7). An orbital abscess appears as a well-defined mass with a low density necrotic center, and an enhancing rim. On MRI, orbital inflammation and edema produce a diffuse signal that is isointense to muscle. On the T2W image, a fluid level may be visible as a layered hyperintense signal in an abscess or sinus. The inflammatory exudate remains hypointense. The necrotic abscess center remains dark, but there is an enhancement of the peripheral rim.
Fig. 1.4.7: Coronal contrast-enhanced computed tomography (CECT) in left orbital cellulitis, showing swollen left extraocular muscles and fat stranding.
Fig. 1.4.8: Axial postcontrast fat suppressed T1-weighted (T1W) magnetic resonance imaging (MRI) with left orbital plexiform neurofibroma showing an infiltrating enhancing soft tissue mass in a patient with neurofibromatosis type 1 (NF1).
Plexiform Neurofibroma
It occurs in about one-third of patients with NF1 (Fig. 1.4.8). It commonly affects the trigeminal nerve, especially the ophthalmic and maxillary divisions. PNF has a multispatial growth pattern, similar to venous and 29lymphatic malformations that follow vessels. The patient's age and relevant history are the key to the correct diagnosis. On imaging, PNF follows the distribution of the involved nerves through fascial boundaries with a characteristic targetoid appearance on T2W images.
Rhabdomyosarcoma
Rhabdomyosarcoma is the most common soft tissue sarcoma of the head and neck in childhood (mean age is 8 years), with 10% of all cases involving in the orbit. Proptosis and blepharoptosis are common presenting symptoms of orbital RMS. Pain is uncommon and may indicate an advanced tumor. Typically, it presents as an extraconal well-defined mass without osseous destruction, however more advanced cases can be both extra- and intraconal and infiltrative with destroy bone. It can involve any part of the orbit, including the EOMs. On noncontrast CT (NCCT), the mass is isodense to muscle. On MR imaging, RMS is typically T2 hyperintense with areas of high T1 signal secondary to hemorrhage, with some contrast enhancement.
MISCELLANEOUS PATHOLOGIES
Intraocular/Intraorbital Foreign Body
Noncontrast CT scan is the imaging modality of choice for evaluation of suspected intraorbital foreign bodies. It has an advantage over the plain radiographs owing to its superior spatial resolution; it can often identify nonmetallic foreign bodies like wood also. Helical CT scans allow precise localization of the foreign body and delineation of its relationship with the surrounding structures (Fig. 1.4.9). MRI is contraindicated for evaluating metallic intraorbital foreign bodies.
Cysticercosis
Ultrasound is often the first-line imaging modality for evaluating suspected cysticercus (Figs. 1.4.10A and B), especially if intraocular. MRI is preferred over CT for identification of myocysticercosis. Orbital cysticercosis on MRI scans appears as a T2 hyperintense cystic lesion often with an eccentric hypointense scolex within the EOM. The muscle itself may be bulky with perilesional T2 hyperintensity suggestive of edema (Figs. 1.4.10A and B). Contrast-enhanced CT (CECT) may show a ring enhancing lesion in one of the EOMs with an eccentric focus of enhancement or calcification representing the scolex.
Fig. 1.4.9: Axial noncontrast computed tomography (NCCT) shows a tiny metallic foreign body just behind the right globe, adjacent to the optic disc. It clearly shows that it is lying in extraocular location.
Orbital Trauma
Computed tomography is the preferred imaging modality for evaluation of orbital and cranial fractures because of its ability to provide detailed bony images in high spatial resolution. A NCCT with bone and soft tissue windows with multiplanar reconstruction is employed (Figs. 1.4.11A and B). Diffuse hyperdense areas suggest acute intraorbital bleed while air pockets represent orbital emphysema. A “blowout” orbital fracture involving the medial wall and floor is a frequent injury. In a pure blowout fracture of the orbital floor, it is displaced downward into the maxillary sinus (Figs. 1.4.11A and B).30
Figs. 1.4.10A and B: Ultrasound (A) and axial T2-weighted (T2W) magnetic resonance imaging (MRI) (B) in myocysticercus showing a cystic intraorbital lesion in the lateral rectus with a hyperechoic center suggesting a scolex (A); another patient showing a swollen medial rectus with a cyst and nodule.
Figs. 1.4.11A and B: Oblique sagittal computed tomography (CT) reconstruction, bone window (A) soft tissue window (B), in two different patients of blowout fracture of the orbit. Note clearly the orbital floor fractures with normal inferior rectus (IR) and tear drop shaped hemorrhage pouting in the maxillary sinus in (A) and entrapped swollen IR in (B).
In children, due to resilient bones, there is often a minimal bony displacement and herniation of orbital contents but inferior rectus may still get entrapped, referred to as “trapdoor fracture”. The muscle may be bulky, heterogeneous with a rounded contour suggesting hematoma or contusion. Medial wall fractures show displacement of the lamina papyracea into the ethmoid air cells often with opacification of the sinus. The medial rectus muscle with intraorbital fat may also be displaced into the fracture site.
Axial images are best for the evaluation of the maxillary antrum, pterygoid plates, zygomatic arches, and the medial and lateral orbital walls. Coronal images are more useful for evaluation of orbital rims, the orbital floor and roof, the cribriform plate, and the skull base. Reformatted images in the orthogonal sagittal and oblique planes are helpful for evaluating subtle orbital apex and optic canal fractures.
Pearl
1.5 ULTRASONOGRAPHY
Asha Samdani, Aditi Dubey
INTRODUCTION
Ultrasonography (USG) has broad application in ophthalmology. In 1793, Lazzaro Spallanzani (Italy) discovered that bats orient themselves with the help of sound whistles while flying in darkness. This was the basis of modern ultrasound application. Two types of devices, are used diagnostically, i.e. A-scan and B-scan. A-scan is a one-dimensional amplitude modulation scan commonly used for measurement of axial length (AL) and pachymetry.
Along with B-scan, it is used to determine the ultrasonic properties such as internal reflectivity, and dimensions of posterior segment masses. B-scan is a two-dimensional, cross-section brightness scan. Its use is primarily to evaluate posterior segment and orbital pathology when the ocular media are cloudy, and a direct view is not possible. High-resolution B-scan or ultrasound biomicroscopy (UBM) uses higher frequency probes (20–50 MHz vs the standard 10 MHz) to provide detailed images of anterior segment structures such as the angle, iris, and ciliary body. This chapter deals with B-scan USG primarily.
For sound to be considered ultrasound, it must have a frequency of greater than 20,000 oscillations per second, or 20 KHz, rendering it inaudible to human ears. Ultrasonography of the eye is an indispensable noninvasive tool in the diagnosis and management of various ocular orbital diseases. It was first used in ophthalmology in 1956 by Mundt and Hughes as A-scan. Baum and Greenwood introduced the first B-scan in 1958. Coleman in the 70s developed the first commercially available B-scan.
PRINCIPLE
Ophthalmic ultrasound (Figs. 1.5.1 and 1.5.2) uses high-frequency ultrasound waves, which are transmitted from probe to eye. Tissue penetration is directly proportional to resolution and inversely to frequency. That is why; USG probes used for Ocular USG are of higher frequency (10 MHz) as it needs much less tissue penetration. As the sound waves strike intraocular structures, they are reflected back to the probe and converted into an electric signal. These signals are subsequently reconstructed as an image on a monitor.
The ophthalmic B-scan probe has high frequencies of 10 MHz and contains piezoelectric crystal. Marker on probe helps in the understanding orientation of the image on the screen (Fig. 1.5.2).
The orientation of the marker (Fig. 1.5.3) is directly correlated to the sound beam orientation. Wherever the marker is directed on the eye represents the upper portion of the echogram (Fig. 1.5.4) and, in most instances, the probe is placed opposite the area of the eye to be examined.
Velocity depends on the density of the medium. Sound travels faster through solids than liquids in aqueous and vitreous = 1,532 m/s, and in cornea and lens = 1,641 m/s (Table 1.5.1).
Reflectivity is higher when the echoes are stronger and thus producing brighter dots. The angle of incidence of the probe is critical. When the probe is held perpendicular to the area of interest, more of the echo is reflected directly back into the probe tip and sent to the display screen. When held oblique to the area imaged, part of the echo is reflected away from the probe tip, and less is sent to the display screen the higher the perpendicularity.
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Absorption: The density of the solid lid structure results in absorption of part of the sound wave when B-scan is performed through the closed eye, thereby compromising the image of the posterior segment.
Shadowing reduction in echo amplitude posterior to a strongly reflecting or attenuating surface can also lead to poor quality of the image.
Gain: The amplification of the display can be altered by adjusting the gain, which is measured in decibels (dB). When the gain is high, weaker signals are displayed, such as vitreous opacities and posterior vitreous detachments (PVDs). When the gain is low, the weaker signals disappear, and only the stronger echoes, such as the retina, remain on the screen.
BASIC SCREENING TECHNIQUE
Probe positions: The probe can be used in the following positions:
- Transverse position: Most commonly used. The probe is positioned parallel 33to limbus (on opposite scleral surface). It demonstrates the lateral extent of pathology (approximately 6 o'clock hours) (Fig. 1.5.4).
- Longitudinal position: The probe is perpendicular to the limbus. It represents the radial extent of pathology and proximity to the optic nerve and demonstrates only 1 o'clock hour that represents optic nerve to the periphery.
- Axial position: Patient is fixating in primary gaze, probe face centered on the cornea. Displays the lens and the optic nerve. Horizontal axial scan-marker is toward the patient's nose. Vertical axial scan-marker toward the 12 o'clock position.
- Oblique position: The patient is asked to look at various gazes and probe is placed at the oblique axis.
An examination performed when there is no view into the eye because of opaque media, and the determination of the status of the posterior segment is required. The highest gain setting must be used to visualize any weak signals, such as vitreous opacities and posterior vitreous detachments, or to gauge the extent of vitreous hemorrhages. If any pathology such as retinal or choroidal detachments (CDs) is found, then the gain may be reduced for better resolution of the stronger signals from these structures. The entire globe must be examined, from the posterior pole out to the far periphery.
Using a limbus-to-fornix approach, the four major quadrants include the 12-o'clock, 3-o'clock, 6-o'clock, and 9-o'clock positions, and each centered on the right side of the echogram in transverse approaches are evaluated. The posterior pole with a horizontal axial scan is evaluated, which incorporates both the optic nerve and the macula in one echogram. If no additional pathology is detected, these five echograms complete the examination.
In case of any posterior pathology is detected during basic screening, it should be centered on the right side of the echogram to achieve the highest resolution. This is accomplished by determining the clock hour represented in the transverse scan where it was discovered. Once determined, the patient should be instructed to redirect his or her gaze to that meridian, with the probe then placed on the opposite scleral surface. The gain is now reduced until the highest resolution is achieved, and photographic documentation is produced.
Macular localizing: The four methods of localizing and centering of the macula are horizontal, vertical, transverse, and longitudinal. In the horizontal and vertical method, the probe is on the corneal vertex and should be aimed straight ahead to center the macula with marker directed nasally in horizontal while the marker is in the 12-o'clock position in the vertical method. In the transverse and longitudinal method, patient fixating slightly temporally and the probe is placed onto the nasal sclera with the marker at the 12-o'clock position in transverse method while toward the limbus or temporally toward the macula in the longitudinal method. These scan bypasses the lens, thereby preventing absorption or reverberation artifacts from an intraocular lens
Indications for B-scan
- Opaque ocular media:
- Anterior segment: For example, corneal opacification, hyphema or hypopyon, miosis, cataract, pupillary or retrolenticular membrane
- Posterior segment: For example, vitreous hemorrhage or inflammation
- Intraocular foreign bodies: For detection and localization.
VIVA QUESTIONS
1. Different examination modes of ultrasonography (USG).
Ans. Various examination modes in ophthalmic ultrasonography are:
- A-scan: Amplitude modulation scan
- B-scan: Brightness modulation scan
- Vector A-scan
- Doppler ultrasonography
- UBM (high-frequency ultrasound).
A-scan: Amplitude modulation scan—salient features are:
- Axial length
- Time-amplitude scan
- Pressure, falsely low AL
- It can also be used for pachymetry
- The frequency of the probe is around 8 MHz
- Quantitative USG:
- Helps to determine the texture of lesion
- Based on reflectivity
- It is semiquantitative (Table 1.5.2).
B-scan (brightness modulation scan):
- Multiple A-scans
- As internal emitter is rapidly swept back and forth
- Two-dimensional (2D)
- Topographic examination for shape, border, location, and extent
- Kinetic USG: Mobility, after movements, vascularity (Valsalva).
- It can assess:
- Vitreoretinal status
- Macula
- ONH
- Anterior two-thirds of orbit
- Extraocular muscle (EOM)
|
Doppler ultrasound:
- Using frequency shifts from acoustic reflections to measure movements, flow conditions within vessels is detected
- Presentation as false color based on the frequency
- Three-dimensional reconstructions.
2. Differences between retinal detachment (RD), choroidal detachment (CD), and posterior vitreous detachment (PVD).
- Retinal detachment: It appears as a highly reflective, attached to the ora serrata anteriorly and the optic nerve (Fig. 1.5.5). It has moderate mobility and translucent subretinal space. Maintains 100% reflectivity even on low gain.
- There is a gradual separation of the membrane from the ocular wall unlike in CD
- Attachment at disc is broad and at the periphery of the disc
- Persists at low gain
- Thickness corresponds to PVR
- Configuration—convex RRD, concave TRD, double layer sign in GRT.
- The configuration of funnel (Figs. 1.5.6 and 1.5.7), retinoschisis
- Coexisting findings can be peripheral retinal looping, cyst formation in long-standing RD (Fig. 1.5.8)
- Tractional RD common finding in vascular retinopathies caused strong adhesion (Fig. 1.5.9) and subsequent traction detached retina—concave appearance35
Table 1.5.3 Differences between RD, CD, and PVD. CDRDPVDTopographyDome shapedLinear, VV, ULocationPeriphery (pre-equator)VariableVariableAttachment to optic discNoYesVariableOthersKissing choroids, vortex veinFolds, breaksInferior, thickerQuantitative (A)Spike height90–100%80–100%40–90%Spike peakDoubleSingleSingleKinetic (A and B)MobilityMinimalModerateMarkedAfter movementAbsentMinimal to moderateMarked(CD: choroidal detachment; PVD: posterior vitreous detachment; RD: retinal detachment) - Giant retinal tears appear as large tears with rolled out tissue and clear breach
- Posterior vitreous detachment: In PVD with the normal eye, the reflectivity is very low, high gain (90 dB) setting is required (Fig. 1.5.10). The reflectivity disappears on lowering the gain under 70 dB. Kinetic echography typically shows a very undulating movement that continues after the eye movements’ stop.
- Attachment at disc narrow or none
- About 40–90% spike height decreasing anteriorly
- The height of PVD generally more superiorly
- Thick PVD spike may persist at low gain
- How to differentiate from RD? Measure the difference in decibels between the 50% spike height of membrane and sclera
- Choroidal detachment: Choroidal detachment is smooth, dome-shaped and thick, no movement seen with eye movement (Fig. 1.5.11). When extensive, one can see multiple dome-shaped detachments, which may “kiss” in the central vitreous cavity.
- Serous CD has anechoic suprachoroidal space
- Seen as thick bright opacity even at low gain
- Sometimes thin stretched cord-like opacity extending between the wall and detached choroidal layer presumed to be vortex vein.
3. Vitreous hemorrhage.
Ans. A fresh mild hemorrhage appears as small dots or linear areas of low reflective mobile vitreous opacities (Fig. 1.5.13). Old vitreous hemorrhage appears vitreous filled with multiple large opacities that are higher in their reflectively and membranes as the blood organizes.
Differentiation between vitreous hemorrhage and asteroid hyalosis: Asteroid hyalosis is calcium deposits in vitreous cavity and appear as bright round signals on B scan with echo-free space in front of the retina.
- Asteroid hyalosis is highly echogenic, and they are still visible when the gain setting is reduced up to 60 dB whereas vitreous hemorrhage which usually disappears by 60 dB.
4. USG appearance of endophthalmitis.
Ans. It depends on the degree and severity of infection and extent of vitreous involvement.
- Low to moderate cases—hyper-reflective opacities noted
- Severe cases—moderate or coarse opacities with membrane formation (Fig. 1.5.14).
5. USG appearance of persistent fetal vasculature:
Ans. It is a congenital abnormality when the fetal hyaloid artery does not resorb. Very thin persistent hyaloidal vessel coursing from the disc to the lens can be seen. Globe size is usually small (Fig. 1.5.15).
6. USG appearance of intraocular foreign body.
Ans:
- A-scan:
- Extremely high reflectivity (100% spike), which persists on low gain (Fig. 1.5.16).
- The distance between the intraocular foreign body and the adjacent sclera is accurately measured at lower system sensitivity.
- Sound attenuation is very strong.
- B-scan:
- Acoustically opaque contrasting with the acoustically clear vitreous.
- Persists even when the system sensitivity is decreased by 20–30 db.
- Topographic and kinetic echography will show if the foreign body is adherent to the retina or if it is floating in the vitreous.
- Sound attenuation is very strong.
- Shadowing of the ocular and orbital tissues behind it as it totally reflects the sound beams preventing its propagation within tissues behind it (Fig. 1.5.16).39
- Associated findings like vitreous hemorrhage, vitreous bands, fibrosis, RD, CD, and even scleral entry wounds can be assessed.
7. USG appearance of posterior staphyloma.
Ans. Appears as a shallow excavation of posterior pole with smooth edges in highly myopic eyes (focal area of thinned sclera) (Fig. 1.5.17).
8. USG appearance of posterior scleritis.
Ans. The degree of scleral thickening can vary from mild to severe. It is commonly, associated edema adjacent to the sclera. This manifests itself as an echolucent area in the tenon space, it forms a “T-sign” USG is the best modality for diagnosis (Figs. 1.5.18A and B).
9. USG appearance of optic nerve pathologies.
Ans.
- Optic disc drusen—appears as an echogenic focus within or on the surface of the optic nerve head (Fig. 1.5.19). Posterior acoustic shadowing may be present with larger lesions. Astrocytic hamartomas may confuse with drusen and can be differentiated by following points:
- Seen in patients with tuberous sclerosis or neurofibromatosis
- Usually unilateral
- Usually larger
- Associated with RD
- Optic nerve head cupping—appears as an excavation of the disc (Figs. 1.5.20 and 1.5.21). It is important to note that USG can detect cupping reliably only in advanced cases.
9. USG appearance of intraocular tumors.
Ans. Ultrasonographic appearance of intraocular tumors has been summarized in Table 1.5.4.
- Choroidal melanoma:
- Mushroom shaped is caused by tumor growth through a break in Bruch's membrane)
- Choroidal excavation (produced by dome-shaped fundus lesions in ultrasound beam path)
Table 1.5.4 Common intraocular tumors in ultrasonography (USG). MelanomaMetastasisHemangiomaShapeDomed, mushroomDomed/bi-domed, irregularDomedLocationVariableNear maculaNear discAssociated RDVariableCommonRareGrowthVariableRapidSlowQuantitative (A)ReflectivityLow/mediumVariableHighInternal structureRegularIrregularRegularSound attenuationStrongVariableWeakKinetic (A)VascularityPresentAbsentAbsent(RD: retinal detachment) - The scleral extension should be watched for
- Choroidal metastasis: The tumor has an irregular outline and heterogeneous internal structure.
- Hemangioma: A scan honeycomb spikes, spikes do not touch baseline.
11. USG appearance of cysticercosis extraocular muscle.
Ans. Extraocular muscle (EOM) cysticercosis manifests as a well-demarcated cyst in relation to the right recti muscle with a central echodense, highly reflective structure within the sonolucent cyst, corresponding to the scolex (Fig. 1.5.23). EOM involvement is the most common variety of orbital cysticercosis. The subconjunctival space is the next common site, followed by the eyelid, optic nerve, retro-orbital space, and lacrimal gland. All the extraocular muscles are involved in myocysticercosis. However, the lateral rectus, medial rectus, and the superior oblique muscles have been found to be affected to a greater extent.
12. USG appearance retinopathy of prematurity (ROP).
Ans.
- Multiple membranes in the periphery
- Retinal detachment (RD)
- Focal fibrovascular fonds
- Open funnel RD
- Closed funnel RD.
13. USG appearance coats.
Ans.
- Unilateral
- RD, turbid SRF.
14. RB (Retinoblastoma)
Ans.
- Solid tumor
- Calcification
- Moderate internal reflectivity
- If necrosis, calcification: High reflectivity (Fig. 1.5.24).
- Sound attenuation moderate to high
- If glaucoma: Globe enlarged.
15. Nucleus drop.
Ans.
- Biconvex-shaped structure (Fig. 1.5.25)
- Surrounding mild to moderate spikes suggesting vitritis.
16. Choroidal coloboma.
Ans.
- Following findings can be there:
- Excavation of posterior layer (Fig. 1.5.26)
- RD (Figs. 1.5.27A to C)
- Small eyeball.
BIBLIOGRAPHY
- Aironi VD, Gandage SG. Pictorial essay: B-scan ultrasonography in ocular abnormalities. Indian J Radiol Imaging. 2009;19(2):109–15.
- Coleman JD, Silverman RH, Lizzi FL, et al. Ultrasonography of eye and orbit, 2nd edition. Lippincott Williams and Wilkins; 2005. pp. 47–122.
- Pushker N, Bajaj MS, Chandra M, et al. Ocular and orbital cysticercosis. Acta Ophthalmol Scand. 2001;79(4):408–13.
Saloni Gupta, Sahil Agrawal, Pranita Sahay
The commonly used instruments in oculoplasty surgery include the following:
- Lid clamp or Snellen's entropion clamp (Fig. 1.6.1)
- Jaeger's lid spatula (Fig. 1.6.2)
- Epilation forceps (Fig. 1.6.3)
- Plain forceps (Fig. 1.6.4)
- Artery (hemostatic) forceps (Fig. 1.6.5)
- Arruga's needle holder (Fig. 1.6.6)
- Stevens tenotomy scissors (Fig. 1.6.7)
- Berke's ptosis clamp (Fig. 1.6.8)
- Well's enucleation spoon (Fig. 1.6.9)
- Enucleation scissors (Fig. 1.6.10)
- Mule's evisceration spatula (Fig. 1.6.11)
- Evisceration curette (Fig. 1.6.12)
- Chalazion clamp (Fig. 1.6.13)
- Chalazion scoop (Fig. 1.6.14)
- Nettleship's punctum dilator (Fig. 1.6.15)
- Bowman lacrimal probe (Fig. 1.6.16)
- Freer periosteal elevator (Fig. 1.6.17)
- Cat's paw lacrimal wound retractor (Fig. 1.6.18)
- Lacrimal sac dissector and currete (Fig. 1.6.19)
- Kerrison bone punch (Fig. 1.6.20)The details of the above-mentioned instruments have discussed in Ophthalmology Clinics for Postgraduates 2016.
PTOSIS
The three categories of surgical procedures most commonly used in ptosis are:
- External approach: Transcutaneous levator advancement
- Internal approach: Levator/tarsus/Müller muscle resection (Putterman müllerectomy, Fasanella-Servat procedure)
- Frontalis muscle suspension using sling.
The most common determining factors in the choice of the surgical procedure for ptosis repair are:
- The amount and type of ptosis
- Levator function
- Surgeon's comfort level and experience with various procedures.
Surgical correction of the levator aponeurosis is preferred in cases with good levator function.
- External (transcutaneous) levator advancement surgery is most commonly used when levator function is normal and the upper eyelid crease is high. In this setting, the levator muscle itself is normal, but the levator aponeurosis (its tendinous attachment to the tarsal plate) is stretched or disinserted, thus requiring advancement. It also allows the surgeon to simultaneously remove excess eyelid skin.
- For repair of minimal ptosis (2 mm)—Putterman müllerectomy if 2.5% phenylephrine test is positive or Fasanella-Servat procedure (requires removal of the superior tarsus).
- Frontalis muscle suspension techniques done in cases where levator function is poor or absent.
Amount of Resection
Berke's Rule
Levator function | Intraoperative lid height |
|---|---|
2–3 mm | At upper limbus |
4–5 mm | 1–2 mm overlap |
6–7 mm | 2 mm overlap |
8–9 mm | 3–4 mm |
10–11 mm | 5 mm overlap |
Beard's Rule
Preoperative margin to reflex distance | Amount of resection |
|---|---|
10–13 mm | 3–4 mm |
14–17 mm | 2–3 mm |
18–22 mm | 1–2 mm |
>23 mm | 0–1 mm |
Complications of Ptosis Surgery
- Overcorrection
- Undercorrection
- Lid contour abnormalities
- Lid lag and lagophthalmos
- Lid crease and fold asymmetry
- Keratopathy
- Infection and/or inflammation
- Hemorrhage.
Complications of Ptosis Clamp
- Oculocardiac reflex (Aschner phenomenon or Aschner-Dagnini reflex) is a known complication. Compression, traction or any manipulation of the extraocular muscles can lead to a sudden decrease in pulse rate/bradycardia.
- Afferent pathway is ophthalmic branch of the Vth cranial nerve via the ciliary ganglion.
- Efferent pathway is the vagus nerve.
- The reflex is mediated by visceral motor nucleus of the vagus nerve in the brain stem, stimulation of which leads to decreased output of the sinoatrial (SA) node of heart causing bradycardia, junctional rhythm, and asystole. Most commonly seen in neonates and children during strabismus correction surgery. However, it can occur with other ocular surgeries and adults.
Management
- Immediate removal of the stimulus can results in the restoration of normal sinus rhythm.
- If not, the use of atropine or glycopyrrolate can revert the attack.
- In severe cases, such as asystole, cardiopulmonary resuscitation (CPR) is required.
- Surgery can be continued if the attack can be reversed successfully.
Materials for Sling Surgery
- Autologous tissue:
- Fascia Lata (both autologous and preserved)
- Palmaris longus tendon
- Temporalis fascia
- Synthetic material:
- Silicone nonabsorbable sutures, Gore-Tex strips (polytetrafluoroethylene), polypropylene (Prolene), polyester mesh, monofilament nylon, and Supramid Extra (polyfilament and nylon).
Management of Residual Ptosis
- The moderate to severe cases of residual ptosis were tackled by levator resection by skin approach which has all the advantages like ease of the proper exposure of levator and its dissection, availability of adequate amount of levator muscle for resection after cutting the horns, and proper lid fold formation is possible.
- The cases of mild ptosis with faint lid folds were managed by proper lid fold formation.
Nonsurgical Management of Ptosis
A dropped eyelid can be managed nonsurgically by:
- External mechanical devices (skin-taping, adhesives, or spectacle-based lid crutches) to retract the upper lid
- Stimulating Müller's muscle (topical eye drops)
- Weakening orbicularis muscle tone (injectable botulinum toxin).
ENUCLEATION
- Current indications of enucleation:
- Intraocular malignancy (uveal melanoma and retinoblastoma)
- Trauma
- Sympathetic ophthalmitis
- Microphthalmos.
- Evisceration versus enucleation: Table 1.6.1 shows difference between evisceration and enucleation.
- Causes of bleeding during enucleation:
- Bleeding from central retinal vessels following optic nerve transection.
- Bleeding from anterior ciliary arteries during muscle transection.
- Hemostasis during enucleation:
- Retrobulbar injection of lignocaine and adrenaline preoperatively can help in intraoperative hemostasis.
- Small amount of bleeding can be controlled by firm digital pressure.
- Use of cautery is rarely required and should be used with caution near the orbital apex to prevent damage to extraocular muscles and oculomotor nerves.
- Postoperatively a pressure patch for the first 48 hours helps in maintain hemostasis.
- Types of enucleation:
- Based on technique:
- Conventional (imbrication) technique of enucleation
- Myoconjunctival technique of enucleation—where extraocular muscles are attached to the respective fornices instead of imbricating over the implant.
- Modifications of conventional:
- 4-petal technique
- Double petal technique
- Scleral patch/orbital fat over porous implants.
- Based on primary or secondary implant.
- Best approach to achieve optimal optic nerve length in retinoblastoma:
- Gentle traction is applied to cause subluxation of globe out of rim.
- Use of blunt 15° curved tenotomy scissors from the lateral aspect to transect the nerve.
- Complications of enucleation:
- Intraoperative:
- Damage to or loss of extraocular muscles
- Hemorrhage
- Extensive dissection and mishandling of conjunctiva and tenons, leading to poor closure.
- Improper implant sizing.
Table 1.6.1 Differences between evisceration and enucleation. EviscerationEnucleationDefinitionSurgical technique of removing the intraocular contents, at the same time preserving the remaining scleral shell, extraocular muscle attachments, and surrounding orbital adnexaSurgical procedure of removal of the entire globe and its intraocular contents, while preserving all other periorbital and orbital structuresIndications- Endophthalmitis
- Penetrating ocular trauma
- Painful blind eye
- Intraocular malignancy (uveal melanoma and retinoblastoma)
- Trauma
- Painful blind eye
- Sympathetic ophthalmitis
- Microphthalmos
AdvantagesShorter duration of surgery- Less complex procedure
- Less disruption of orbital tissues
- Improved postoperative prosthesis motility and better orbital volume
- In cases of infection, less chance of spread to central nervous system (CNS)
- Less painful more cost-efficient
- Lesser risk of sympathetic ophthalmitis
- Lesser risk of intraocular tumor dissemination
Table 1.6.2 Types of exenteration. TypesContents removedAnterior exenteration/extended enucleationGlobe, posterior lamella of eyelid, and conjunctival sacLid sparing exenteration/subtotal exenterationOrbital contents including periosteum of orbital wallsTotal exenteration/eyelid sacrificingOrbital contents, periorbita and lidsRadical/extended exenterationDissection involves paranasal sinuses, face, jaw, palate, and skull base
- Postoperative:
- Infection
- Hemorrhage
- Wound dehiscence
- Extrusion of the conformer
- Contraction of the fornices
- Exposure, extrusion or migration of the implant
- Ptosis
- Hollow or deep superior sulcus
- Poorly fitting prosthesis
- Enophthalmos
- Socket contracture
- Postenucleation socket syndrome
- Orbital cellulitis.
- Calculate the size of implant:
- Formula for enucleation implant size:
Implant diameter = Axial length-2 mm- Subtract 1mm from the above implant diameter for evisceration or hyperopia.
- With a proper sized implant, almost no chances of superior sulcus deformity or enophthalmos.
- The implant replaces the volume, leaving space for prosthesis 1.5–2.5 mL.
- Types of implant:
- Nonintegrated [silicone, acrylic, and semi-integrated implants (Universal and Iowa) polymethyl methacrylate (PMMA)] and integrated (hydroxyapatite, porous polyethylene, and bioceramic).
- Buried and exposed implants.
- Exenteration: Exenteration is a surgical procedure involving removal of the entire globe and its adnexa (including muscles, fat, nerves, and eyelids). Types of exenteration are shown in Table 1.6.2.
EVISCERATION
- Current indications of evisceration:
- Blind painful eye
- Endophthalmitis
- Phthisis bulbi
- Staphylomatous globe
- Severe traumatic injury
- End-stage glaucoma.
- Difference between enucleation and evisceration: As answered above in Table 1.6.1.
- Causes of bleeding during evisceration: From retained uveal tissue.
- Hemostasis during evisceration:
- Subconjunctival injection of lignocaine and adrenaline preoperatively can help in intraoperative hemostasis.
- Complete removal of uveal tissue adherent to scleral shell.
- Inner side of empty scleral cup should be cleaned with sponge soaked in absolute alcohol aids in removing residual uveal tissue.
- Small amount of bleeding can be controlled by firm digital pressure.
- In case of excessive bleeding, cautery can be used.
- Types of evisceration: Two-flap technique and four-flap technique.
- What is anophthalmic socket?
- Anophthalmic socket is defined as the absence of the globe and ocular tissue from the orbit.
- Types of implant: See enucleation.
CHALAZION
- Nonsurgical management of chalazion:
- Warm compresses and lid hygiene.
- Tetracycline class of antibiotics [nonantimicrobial effects—inhibiting polymorph degranulation, reducing meibomian secretion viscosity, decreasing collagenase production, and inhibiting matrix metalloproteinase-9 (MMP-9) activity].
- Topical steroids—to prevent the chronic inflammatory response.
- Local intralesional injection of a steroid (triamcinolone or methylprednisolone)—reduces inflammation and cause regression of the chalazion.
- Intralesional steroid: agents, dose, technique, indication, and complication:
- Local intralesional injection of a steroid (triamcinolone or methylprednisolone) 0.2 mL of 40 mg/mL into the chalazion's center.
- Indications:
- As an alternative first-line treatment when biopsy is not required
- When the lesion is located near the lacrimal drainage system
- Where an incision could cause complications involving tear flow.
- Complications: Hypopigmentation and atrophy of the area, a visible depot of medication, corneal perforation, traumatic cataract, elevated intraocular pressure, and bacterial or viral infections.
-
- Adequate curettage and drainage may prevent recurrences.
- Cauterization of the meibomian gland with a hyfrecator, phenol or trichloroacetic acid, and helps in preventing recurrences.
- Long-term low-dose tetracycline class therapy frequently has also been shown to prevent recurrence.
- Approaches for excision:
- Transconjunctival vertical incision—to avoid damage to nearby glands.
- External (skin) horizontal incision—if a chalazion threatens to break through the skin or has drained through.
DACRYOCYSTORHINOSTOMY
- Valves in nasolacrimal duct (NLD) system and their clinical importance?
- Valves in NLD system: The mucous membrane folds in the lacrimal pathways form a type of valve and serve to block the backward tear outflow.
- Valve of Rosenmüller: It is a fold of mucosa at the junction between common canaliculi and lacrimal sac. It prevents reflux of tear from sac back into canaliculi.
- Valve of Hasner: It is located at the junction of the opening of duct into inferior meatus of nose. It prevents sudden blast of air entering the lacrimal sac while blowing the nose.
- Other valves: Valve of Huschke, Bochdalek, Folta, Krause, Hyrtl, Taillefer.
- Lengths/distance of surgically important landmarks in NLD system:
- The NLD is located, on average, 24.6 ± 3.56 mm posterior to the anterior nasal spine.
- The marginal vessels lie medial to medial canthus while angular vein lies 8 mm medial to medial canthus. Thus, it is important to plan the skin incision and dissect tissues carefully.
- The uncinate process is attached just posterior to the NLD, which is only 4 mm anterior to the maxillary sinus ostium.
- Maxillary sinus ostium is also an important landmark to determine the location of the NLD.
- What is false passage in probing?At the time of probing, lacrimal probe may pierce through and go into a different track instead of NLD system creating a false passage.
- What is the size of probes preferred in congenital nasolacrimal duct obstruction?Size: 0–00
- Lacrimal sac dimensions and parts:
- Lacrimal sac:
- Length 15 mm
- Breadth 5–6 mm
- Volume 20 mm3
- Parts:
- Fundus (3–5 mm)—portion above the opening of canaliculi
- Body (10–12 mm)—middle part
- Neck—lower small part
- What is lacrimal pump?
- Lacrimal pump is a system helping in tear drainage.
- In the relaxed state, the puncta lie in the tear lake.
- With eyelid closure, the orbicularis oculi muscle contracts. The pretarsal orbicularis squeezes and closes the puncta and canaliculi. The preseptal orbicularis, which inserts into the lacrimal sac, pulls the lacrimal sac open and draws the tears into the sac by creating a negative pressure within sac.
- With eyelid opening, the orbicularis relaxes, the puncta open, and the lacrimal sac collapses, propelling tears down the duct. Simultaneously, with the puncta opened, the canaliculi refill, completing the cycle.52
Table 1.6.3 Advantages and disadvantages of endoscopic dacryocystorhinostomy (DCR). AdvantagesDisadvantagesNo external scarRequires extensive knowledge of endonasal anatomyEndonasal anatomy is directly visualizedRequires skillsIn cases of primary failure, scar tissue under direct visualization can be easily mendedIncreased operative timeIf indicated concomitant sinus surgery performedExpensive equipment
- Muscles of lacrimal pump mechanism:
- Horner's muscle (pars lacrimalis): Fibers of pretarsal portion arising from lacrimal fascia and upper part of post lacrimal crest. They help in draining tears by lacrimal sac
- Muscle of Riolan (pars ciliaris): Fibers of pretarsal portion which run along lid margins behind ciliary follicles. They keep lid in close opposition to globe.
- What is percentage of tear drainage through upper and lower puncta?70% tear enter the lower canaliculus while 30% enter the upper.
- Types of dacryocystorhinostomy (DCR):
- External DCR
- Endonasal DCR
- Transcanalicular endoscopic DCR
- Conjunctival DCR
- Canalicular DCR.
- Advantage and disadvantage of endoscopic dacryocystorhinostomy.
- Site of ostium in DCR:
- The bony ostium is initiated at the junction of lacrimal bone and lamina papyracea.
- Extension:
- Superiorly: About 2 mm above the medial canthal tendon (MCT)
- Inferiorly: Till the upper edge of NLD
- Posteriorly: Including the lamina papyracea
- Anteriorly: Till 3–4 mm above the level of anterior crest.
- What is sump syndrome?
- Lacrimal sump syndrome occurs as result of incomplete opening of inferior portion of the lacrimal sac, or the bone adjacent to the inferior sac, such that dependent fluid continues to collect in the sac. It can also result when mucosal healing leads to reapproximation of cut surfaces.
- It is an uncommon cause of failed DCR.
- Describe indications of intubation DCR.Not indicated in uncomplicated DCR as tube induced granulation tissue formation can itself cause closure of anastomosis.Indications of intubation DCR are as follows:
- Canalicular stenosis
- Fibrosed sac with inadequate mucosal flaps
- Repeat DCR
- Loss of mucosal flaps during surgery
- Different types of intubation tubes (stents).Two main types of stents are bicanalicular and monocanalicular.
- Bicanalicular stent: Pass through both the upper and lower canaliculus. For example Crawford stent, Ritleng stent, Pigtail/Donut stent, and Kaneka Lacriflow stent.
- Monocanalicular stents: Do not provide a closed loop system, only intubating either the upper or lower canaliculus. Types—Mini-Monoka stent and Jones tube.
- Cerebrospinal fluid rhinorrhea in DCR:
- Cerebrospinal fluid (CSF) leakage or rhinorrhea is a very rare complication of DCR
- The cause of CSF leak after external DCR can either be the direct or indirect mode of bone injury. Inadvertent extension of the osteotomy to the anterior part of the base of the skull can produce direct injury
- With the development of new surgical procedures such as endoscopic DCR the incidence of iatrogenic CSF rhinorrhea has increased
- It is more likely to occur during a pediatric DCR as children have low lying cribriform plate as compared to adults.
- Most of the iatrogenic CSF leaks resolve within 7–10 days with conservative management. The main goal of management of CSF rhinorrhea is to prevent ascending meningitis.
- Rate of failed DCR: The failure of DCR in most series is less than 10% of cases.
- Difference between DCR and dacryocystectomy (DCT)
- Dacryocystectomy is a surgical procedure of complete extirpation of the lacrimal sac.
- It was the standard of care for management of dacryocystitis and lacrimal fistulas before the advent of DCR.
- Appropriate age for massage, probing, and DCR in congenital NLDO?
- Conservative management (Crigglers’ sac massage) of congenital NLDO up to 6–12 months of age
- Nasolacrimal duct probing (therapeutic):
- 12–18 months if conservative treatment fails
- Before 1 year in special cases (mucocele, prior to intraocular surgery, and repeated episodes of dacryocystitis)
- Dacryocystorhinostomy—after at least three trial of failed probing.
- How to confirm that regurgitated fluid is from sac not canaliculus?
- Regurgitated fluid from canaliculus is clear fluid whereas from sac is mucoid/pus.
- It can be confirmed by dacryocystography.
