INTRACRANIAL CALCIFICATION
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Fig. 1B: Axial computed tomography (CT) images showing extensive intraparenchymal calcification in a case of Fahr's disease.
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Fig. 3: Axial CT image in a case of congenital cytomegalovirus (CMV) shows bilateral symmetrical periventricular calcification.
Fig. 4: Axial CT image in a 10-year-old boy with tuberous sclerosis shows bilateral calcified subependymal nodules and a partially calcified tuber in left frontal lobe.
DIFFERENTIAL DIAGNOSIS OF BRAIN LESIONS
Supratentorial Midline Tumors
- Optic and hypothalamic glioma
- Craniopharyngioma
- Astrocytoma
- Pineoblastoma
- Germinoma
- Lipoma
- Teratoma
- Pituitary adenoma
- Meningioma
- Choroid plexus papilloma.
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Supratentorial Midline Cysts
- Cavum septum pellucidum (5th ventricle)
- Cavum vergae (6th ventricle)
- Cavum velum interpositum
- Arachnoid cyst in the region of the quadrigeminal plate cistern
- Vascular lesions (aneurysm)
- Cholesterol granuloma
- Pineal cyst
- Rathke's cleft cyst
Supratentorial Paramidline Cysts
- Epidermoid
- Trichilemmal cyst (sebaceous)
- Leptomeningeal cyst
PSEUDOMASSES OF BRAIN
Pseudomasses of brain are shown in Table 5.
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INTRACRANIAL MASSES
Details of intracranial masses are shown in Table 6.
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NONTUMORAL BRAIN LESIONS
Nontumoral brain lesions are given in Table 7.
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Fig. 8: Contrast-enhanced computed tomography (CECT) axial image of head hypodense area with loss of gray-white matter differentiation in a case of head trauma suggesting nonhemorrhagic contusion.
WHITE AND GRAY MATTER LESIONS
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Multifocal White Matter Lesions
- Virchow-Robin spaces (when bilateral and diffuse, these are called Etate Crible)
- Demyelinating diseases (vascular, postinfectious) (Table 9)
- Multiple sclerosis (MS)
- Diffuse axonal injury
- Cysticerci
- Abscesses
- Leukoencephalopathy
- Neurocutaneous syndromes [tuberous sclerosis, neurofibromatosis-1 (NF-1)]
- Multifocal glioma
- Gliomatosis cerebri
- Metastases.
Periventricular Hypodensity
- Gliosis
- Encephalomalacia
- Porencephaly
- Resolving hematoma
- Infarct
- Interstitial seepage of cerebrospinal fluid (CSF) in hydrocephalus
- Multiple sclerosis
- Migraine
- Vasculitis
- Encephalitis
- Acute disseminating encephalomyelitis
- Diffuse necrotizing leukoencephalopathy
- Progressive multifocal leukoencephalopathy
- Virchow-Robin space
- Leukodystrophy.
Brainstem Hypodensity
Brainstem hypodensity is given in Table 10.
- Physiological
- Syringobulbia
- Infarction
- Central pontine myelinolysis
- Gliosis
- Glioma
- Metastases
- Granuloma.
Bilateral Focal/Diffuse Hypodensities Basal Ganglia
- Physiological (VR spaces)
- Infection (TB, HIV)/infestation (toxoplasmosis, cryptococcosis)
- Arterial infarct (lacunar infarcts)
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Fig. 9: Axial CT image shows lentiform shaped acute extradural hematoma along the lateral parietal convexity.
Fig. 10: Axial CT image showing acute subdural hematoma along right frontoparietal lateral convexity with a coincidental small hemorrhagic contusion in right parietal lobe.
- Hypoxic—ischemic encephalopathy
- Metabolic encephalopathy (severe hypoglycemia, osmotic myelinolysis)
- Toxic encephalopathy (methyl alcohol, CO, cyanide)
- Inherited disorders (Alexander disease, Canavan disease, Hallervorden Spatz disease, Huntington disease, Leigh disease, metachromatic leukodystrophy, methylmalonic aciduria, Wilson disease)
- Acquired neurodegenerative disorders (MS, Parkinson disease, striatonigral degeneration).
Bilateral Hyperdense (Calcification) Basal Ganglia
- Idiopathic (Globus pallidus is most commonly affected)
- Fahr disease
- Toxic causes: CO poisoning, lead poisoning, mineralizing angiopathy.
- Secondary to infection (TB, HIV, TORCH)/infestation (toxoplasmosis, cysticercosis)
- Congenital disorders (Cockayne syndrome, Down syndrome, MELAS/MERRF (mitochondrial encephalopathy with lactic acidosis/myoclonic epilepsy with ragged red fiber) syndrome, methemoglobinopathy, neurofibromatosis, tuberous sclerosis)
- Metabolic: Hypoparathyroidism, pseudohypoparathyroidism, pseudopseudohypothyroidism, hyperparathyroidism.
- Miscellaneous: Postradiotherapy/chemotherapy.
Hyperdense Falx
- Subarachnoid hemorrhage (associated with sulcal bleed in the parasagittal brain parenchyma)
- Subdural hemorrhage
- Diffuse cerebral edema (there is pseudohyperdensity due to diffusely hypodense brain parenchyma)
- Dural calcification (usually seen in the elderly population)
Ring Enhancing Lesions Crossing the Corpus Callosum
- Glioblastoma multiforme (butterfly glioma): More heterogeneous with areas of necrosis and hemorrhage
- Astrocytoma
- Oligodendroglioma:
- Lymphoma: Primary lymphoma is usually homogeneous and does not show necrosis/hemorrhage. Secondary lymphoma or lymphoma associated with immunocompromised states (AIDS) show necrosis.
Innumerable Small Enhancing Brain Nodules (Table 11)
- Disseminated infection: Tuberculosis (TB), neurocysticercosis (NCC), and histoplasmosis
- Inflammation: Sarcoidosis, MS
- Primary CNS lymphoma
- Metastases
- Subacute multifocal infarction: Hypoperfusion, multiple emboli, cerebral vasculitis, meningitis, cortical vein thrombosis.
Gyriform Enhancement (Table 12)
- Infarct
- Leptomeningitis (Fig. 11)
- Sequelae to subarachnoid hemorrhage
Pneumonic for Ring Enhancing Lesions in Brain
MAGICAL DR
M: | Metastasis |
A: | Abscess |
G: | Glioblastoma |
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Fig. 11: Coronal MPR CT image with nodular enhancement of the leptomeninges and ependymal enhancement.
Fig. 12: Axial CT image showing a ring-enhancing lesion with perilesional edema in the left frontoparietal region.
I: | Infarct (subacute phase) |
C: | Contusion |
A: | AIDS |
L: | Lymphoma |
D: | Demyelinating disease |
R: | Radiation necrosis or resolving hematoma |
Multifocal Brain Tumors and Tumor-like Lesions
- Infections and infestations [tuberculoma, toxoplasmosis, NCC, multiple abscesses (pyogenic/fungal)]
- Multiple sclerosis
- Phakomatosis
- Metastases from primary CNS tumor
- Multicentric CNS lesion: True multicentric glioma, primary CNS lymphoma
- Multicentric meningioma without neurofibromatosis.
VENTRICULAR LESIONS
Ventricular Enlargement
- Hydrocephalus
- Holoprosencephaly
- Hydranencephaly
- Schizencephaly
- Porencephaly
- Encephalomalacia
- Deep cortical atrophy.
Small Ventricles
- Physiological variation (sulci and cisterns appear normal)
- Chronic ventricular shunt drainage (sulci and cisterns appear normal)
Abnormal Ventricular Configuration
- Colpocephaly (dilatation of the trigone and occipital horns of the lateral ventricles):
- Corpus callosal agenesis
- Arnold-Chiari malformation
- Holoprosencephaly (lobar type).
- Abnormal frontal horns:
- Square or box-like—absence or hypoplasia of septum pellucidum (septo-optic dysplasia, callosal dysgenesis, schizencephaly, holoprosencephaly)
- Convex or flat lateral wall (caudate lobe atrophy).
- Miscellaneous:
- Schizencephaly (nipple-like elevation along the lateral wall)
- Porencephaly
- Corpus callosum dysgenesis (high riding third ventricle with communication with a dorsal interhemispheric cyst)
- Chiari II malformation (elongated, slit-like fourth ventricle)
- Dandy-Walker syndrome (communication between the fourth ventricle and the retrocerebellar cyst) (Figs. 13A and B)
- Dandy-Walker variant (slit-like communication between the fourth ventricle and the cisterna magna with a typical key-hole appearance) (Figs. 14A and B)
- Ventricular diverticulum (CSF-outpouching from the medial atrial wall of the lateral ventricle)
- Herniation
- Subfalcine: It is characterized by displacement of the lateral and third ventricle under the falx away from the side of mass lesion with dilatation of the contralateral lateral ventricle (Fig. 15).
- Transtentorial herniation: There is change in size and configuration of the fourth ventricle depending upon the ascending or descending transtentorial herniation. Ascending type is associated with compression and displacement of the third ventricle and its aqueduct as well while descending type is characterized by dilatation of the ambient, quadrigeminal, and cerebellopontine cisterns and rotation of the brainstem.31
Figs. 14A and B: CECT axial images of head showing hypoplastic vermis and fourth ventricle communicating with cisterna magna in a case of Dandy-Walker variant.
Hydrocephalus
- There is enlargement of part or entire ventricular system with proportionate enlargement of the temporal horns of the lateral ventricles (Fig. 16)
- There is rounding of the frontal horns of the lateral ventricle
- There is effacement of the basal cisterns, fissures, and the sulcal spaces to a varying degree
- There is transependymal seepage of the CSF resulting in periventricular hypodensity in moderate and severe cases
- The dilated ventricles are always surrounded by cortical mantle irrespective of the severity.
Fig. 15: Axial CT image showing subfalcine herniation of the right lateral ventricle to the left side in a patient with acute SDH on right side with a small aerocele.
Holoprosencephaly
The CT appearance varies with the type of the holoprosen-cephaly.
Alobar Type
It is characterized by:
- Single, large, crescentic ventricle devoid of horns
- Large dorsal cyst with a wide communication with the ventricle
- Grossly distorted supratentorial brain morphology with no hemispheric development and absence of the interhemispheric fissure, falx, and tentorium, septum pellucidum, third ventricle, corpus callosum, Sylvian fissure, straight sinus, vein of Galen, and internal cerebral veins
- Fused thalami and basal ganglia protruding into the ventricle
- Midbrain, pons, and cerebellum are morphologically normal
- Associated abnormalities include cyclopia, ethmocephaly, cebocephaly, cleft lip, and palate.
Semilobar Type
It is characterized by:
- Single, large ventricle with rudimentary or poorly developed temporal and occipital horns
- Large dorsal cyst with a wide communication with the ventricle
- Supratentorial brain morphology is distorted with no hemispheric development and rudimentary interhemispheric fissure (separating occipital lobes), falx, and tentorium, third ventricle, but with absence of septum pellucidum and corpus callosum, Sylvian fissure, straight sinus, vein of Galen, and internal cerebral veins
- There is partial separation of the thalami and basal ganglia that are anterior relative to their usual location
- Cortical mantle seen is thicker than in alobar type and is pachygyric
- Midbrain, pons, and cerebellum are morphologically normal
- Associated abnormalities include cleft lip and palate.
Lobar Type
It is characterized by:
- Two distinct, well-formed lateral ventricles with closely apposed bodies
- The ventricles are dilated with relatively greater enlargement of the occipital horns of the lateral ventricle
- The frontal horns are fused due to absence of the septum pellucidum and dysplastic frontal lobes, falx, and interhemispheric fissure
- Sylvian fissures are absent
- Thalami and basal ganglia may be fused or separated
- Cortical mantle is usually pachygyric and lissencephalic
- Midbrain, pons, and cerebellum are morphologically normal
- Associated abnormalities include cleft lip and palate.
Hydranencephaly
- There is a large CSF—isodense, cystic lesion surrounded by a membrane with no identifiable brain tissue usually involving one half of the cranial cavity
- Hemispheric division is usually maintained
- Except for the atrophic brainstem, rest of the brain appears morphologically normal even on the side of the cyst
- Ventricle with the choroids plexus are usually preserved.
Atrophy
- It is characterized by symmetric enlargement of the ventricular system with proportionate enlargement of the basal cisterns, fissures, sulcal spaces, and the other CSF spaces in the cranial cavity
- It is associated with loss of volume of both gray and white matter with reduction in gray white matter differentiation.
Corpus Callosum Agenesis (Fig. 17)
- It is characterized by absence of corpus callosum, cingulated gyrus, and sulcus with a high riding third ventricle opening into the interhemispheric fissure. A cyst may or may not be present.
- The medial hemispheric surface of the brain shows a radial arrangement of the gyri and sulci in a spoke-wheel like configuration.
- Abnormal upward course of the anterior cerebral arteries (ACAs).
- The lateral ventricle are arranged parallel to each other (Racing car sign)with pointed frontal horns (Viking horn sign) and dilated atria and Brain occipital horns
Fig. 17: Axial CT image shows parallel oriented lateral ventricles with colpocephaly with absence of corpus callosum.
- With partial agenesis, rostrum and splenium of the corpus callosum are hypoplastic or absent with varying degrees of development of the body and genu.
Arnold-Chiari Malformation
- Type II is the classical type in this group and is commonly associated with colpocephaly
- It is characterized by small posterior fossa, with low lying transverse sinuses and concave clivus and petrous ridges
- There is beaking of tectum, creeping of cerebellum around brainstem with inferiorly displaced vermis and medullary spur and kink
- There is hydrocephalus with tube-like, elongated fourth ventricle
- Meningomyelocele is invariably seen with syringomyelia and diastematomyelia in many cases
DIFFERENTIATING FEATURES OF BRAIN LESIONS
Differentiating features of brain lesions are listed in Table 13.
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MISCELLANEOUS LESIONS OF THE BRAIN
Intraparenchymal Hemorrhagic Lesions in Brain
Hemorrhagic lesions in brain can be broadly categorized into:
- Nontraumatic:
- Hypertension
- Aneurysm and vascular malformation (AVM, cavernous angioma)
- Perinatal hemorrhage
- Hemorrhagic infarction (reperfusion or venous)
- Neoplastic
- Miscellaneous:
- Amyloid angiopathy
- Coagulopathies and blood dyscrasias
- Drug abuse
- Eclampsia
- Infections (vasculitis, encephalitis, abscess, endocarditis with septic emboli)
- Traumatic:
- Diffuse axonal injury
- Cortical contusions
- Deep cerebral and brainstem lesions.
CT Findings of Hemorrhage
- Acute hemorrhage (0–72 hours): It appears hyperdense to human brain. Unretracted semiliquid clot appears hypodense within the hyperdense acute hematoma, giving rise to the so-called swirl sign.
- Subacute hemorrhage (4–14 days): Subacute hemorrhage becomes virtually isodense with the adjacent brain parenchyma. It may sometimes show a peripheral postcontrast enhancement.
- Chronic hemorrhage (>2 weeks): It appears hypodense to the adjacent brain. High attenuation within chronic hematomas is usually secondary to the rebleeding. Rim enhancement around a resolving hematoma typically appears within a few days and disappears between 2 and 6 months.70A target sign on postcontrast images can be seen if rehemorrhage takes place within an organizing hematoma; if rebleeding occurs outside an organized hematoma, it can resemble a tumoral hemorrhage.
Hypertensive ICH
- Hypertensive intracerebral hemorrhages (HICH) are the most common nontraumatic cause in adults (Fig. 40)
- Most are associated with systemic hypertension and in some, ruptured microaneurysms are implicated
- Common location include putamen/external capsule followed by thalamus, pons, cerebellum, and subcortical white matter in the decreasing order of frequency.
Aneurysm and Vascular Malformation (AVM, Cavernous Angioma)
Hypertensive intracerebral hemorrhage (Figs. 41A to C):
Figs. 41A to C: Axial and sagittal CT images showing a large AV malformation with an aneurysm and hematoma.
- Acute SAH is characterized by hyperdensity in the subarachnoid spaces (basal cisterns, fissures, sulci) (Figs. 42A and B)
- Although SAH tends to be diffuse; more focal cisternal or parenchymal hematomas can be due to ruptured aneurysms and are helpful in localizing the bleeding source
- Blood in the Sylvian fissure—aneurysm on the I/L ICA.
- Focal interhemispheric blood—Anterior com artery aneurysm
- Blood in the fourth ventricle—Posteroinferior cerebellar artery aneurysm
- ICH secondary to AVM are usually seen in children or normotensive young adults
Fig. 42: Axial CT images showing posterior interhemispheric acute SDH and SAH in the right frontal lobe.
- Cavernous angiomas typically have a popcorn-like appearance with calcification and mixed signal foci inside a hemosiderin ring.
Perinatal Hemorrhage
- In term infants, it is usually the result of hypoxic-ischemic insult
- Areas of hemorrhage are typically seen in the posterolateral lentiform nuclei and ventral thalamus
- Although the cortex can be involved in profound asphyxia, it is relatively spared compared to the deep gray matter
- In premature infants, germinal matrix hemorrhage (GMH) is the most common form of ICH followed by intraventricular and intraparenchymal hemorrhage that are usually secondary to the former.
- Germinal matrix hemorrhage is divided into four grades:
- Grade II: Hemorrhage ruptured into a normal-sized ventricle
- Grade III: Intraventricular hemorrhage with hydrocephalus (Figs. 43A and B)
- Grade IV: Hemorrhagic extension into the adjacent hemispheric white matter.
Hemorrhagic Infarction (Reperfusion or Venous)
- Hemorrhagic infarction is usually the result of lysis of embolus/opening of collaterals/restoration of normal blood pressure following hypotension/hypertension/anticoagulation causing extravasation in reperfused ischemic brain
- It is seen in approximately 6% of brain infarcts and is usually at the corticomedullary junction
- CT will show the hyperdensity within a previously imaged hypodense acute ischemic infarct
- Venous infarctions are usually hemorrhagic, bilateral, and occur primarily in the white matter and are most often associated with cortical vein and dural sinus thrombosis
Neoplastic
- Common brain tumors that are commonly associated with hemorrhage include: pituitary adenomas, high-grade gliomas, PNET, epidermoid and metastases from bronchogenic, and renal, chorio- and melanocarcinoma.
- Points of benign versus malignant hemorrhage:
- There is no absolute criteria
- Tumors are complex and heterogeneous
- Benign lesions usually have a complete hemosiderin ring
- Nonhemorrhagic areas of the tumor enhance on postcontrast images
- Hemorrhage evolution is disordered or delayed in tumoral lesions in contrast to an orderly evolution seen in benign hemorrhage
- Edema/mass effect resolve with resolution of hematoma in benign lesions while it will persist with malignant lesions
- Hemorrhagic metastatic deposits will be multifocal.
Amyloid Angiopathy
- This is probably the most common cause of recurrent bleeding in normotensive elderly and the incidence increases with advancing age
- Hemorrhages are characteristically multiple, spare the basal ganglia and brainstem, and are located at the corticomedullary junction
- Computed tomography findings of multiple peripherally located hemorrhages of different ages in an elderly normotensive patient strongly suggests the cause as amyloid angiopathy.
Inflammatory Disease and Vasculitis
- Such lesions include infective endocarditis with septic emboli, fungal vasculitis, and necrotizing lesions as herpes encephalitis
- Aspergillosis and other fungal infections may directly invade the vessel wall and cause thrombosis, Hemorrhage, or cerebral infarction
- Type II herpes simplex encephalitis is the most prone to develop hemorrhage especially in neonatal herpes.
Drug Abuse
- Drugs like cocaine can induce a hypertensive episode in which case the location of ICH is similar to that in hypertensive ICH
- Cocaine also promotes arterial and dural sinus thrombosis producing venous infarction and ischemic infarction with subsequent hemorrhage
- Vasculitis with hemorrhage is seen commonly with amphetamines and phenylpropanolamine and less commonly with cocaine.
Blood Dyscrasias and Coagulopathies
- Common causes of noniatrogenic coagulopathy include vitamin K deficiency, hepatocellular disease, antibodies that react to clotting factors, and disseminated intravascular coagulation (DIC). Iatrogenic causes include mainly anticoagulants as heparin, warfarin, thrombolytic agents as streptokinase, antiplatelet agents as aspirin, etc.
- Imaging findings in most coagulopathies are similar.
- Although bleeding can occur at any location, the most common site is supratentorial and intraparenchymal with multifocal lesions with fluid—fluid levels within the hematomas.
Eclampsia
- Posterior circulation is particularly prone
- The occipital lobes are a frequent location of cortical and subcortical lesions
- CT scans will reveal multiple hypoattenuating foci or hemorrhages in the subcortical white matter or basal ganglia.
Diffuse Axonal Injury
- Diffuse axonal injury (DAI) is most common form of the intra-axial primary traumatic lesion
- It tends to occur in the lobar white matter, corpus callosum, and dorsolateral aspect of the brainstem
- Nearly two-thirds are seen at the gray white matter junction, most often in the frontotemporal region, splenium and posterior body of the corpus callosum
- Early CT scans may be unremarkable. Delayed scans in acute DAI may reveal petechial hemorrhages in the location mentioned above.
Cortical Contusions
- It is the second most common form of the intra-axial primary traumatic lesion (Figs. 44A and B)
- Majority involve the temporal lobes followed by the frontal lobes and other sites as the cerebellar hemispheres
- Early findings include patchy, ill-defined, frontal or temporal hypodense lesions that may be mixed with smaller hyperdense foci of petechial hemorrhages
- Delayed scans at 24–48 hours may reveal hemorrhages developing in the previously hypodense regions.
Deep Cerebral and Brainstem Lesions
- Computed tomography is often normal in these patients
Conditions Primarily Presenting as Cerebral Atrophy (Table 14)
- Alzheimer's disease
- Pick's disease
- Vascular dementia
- Extrapyramidal disorders
- Subcortical dementia
- Dyke-Davidoff-Masson syndrome.
Conditions Primarily Presenting as Cerebellar Atrophy (Table 14)
- Diffuse brain atrophy in the elderly
- Secondary to previous infarct/trauma
- Phenytoin toxicity (involves mainly the cerebellar hemispheres)
- Ethanol toxicity (involves mainly the cerebellar vermis)
- Olivopontocerebellar degeneration
- Paraneoplastic cause (secondary to oat cell carcinoma of the lung)
- Postradiotherapy.
Effaced Basal Cisterns
Enhancing:
- Meningitis especially tuberculous
- Leptomeningeal carcinomatosis (usually nodular enhancement)
- Sarcoidosis (thickened leptomeninges).
Nonenhancing:
- Subarachnoid hemorrhage (isodense to hyperdense cisterns)
- Cerebral edema
- Diffuse axonal injury
- Hydrocephalus
- Racemose NCC (cystic, septated appearance of cisterns).
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DIFFERENTIAL DIAGNOSIS OF CEREBELLOPONTINE ANGLE MASSES (TABLE 15)
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DIFFERENTIAL DIAGNOSIS OF INFRATENTORIAL LESIONS (TABLE 16)
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DIFFERENTIAL DIAGNOSIS OF SUPRATENTORIAL MASS LESIONS (TABLE 17)
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DIFFERENTIAL DIAGNOSIS OF WHITE MATTER DISEASES (TABLE 18)
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