Essential Pathology for Dental Students Harsh Mohan, Sugandha Mohan
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The Cell in Health and Disease
  • Chapter 1: Introduction to Pathology
  • Chapter 2: Cell Structure and Function, Cellular Ageing
  • Chapter 3: Cellular Adaptations
  • Chapter 4: Cell Injury: Etiology and Pathogenesis
  • Chapter 5: Morphology of Cell Injury: Degenerations and Cell Death
  • Chapter 6: Intracellular Accumulations
  • Chapter 7: Amyloidosis
  • Chapter 8: Genetic and Paediatric Diseases
  • Chapter 9: Environmental, Nutritional and Vitamin Deficiency Disorders

Introduction to Pathology1

The word ‘Pathology’ is derived from two Greek words—pathos (meaning suffering) and logos (meaning study). Pathology is, thus, scientific study of changes in the structure and function of the body in disease. In other words, pathology consists of the abnormalities in normal anatomy (including histology) and normal physiology owing to disease. Another commonly used term with reference to study of diseases is ‘pathophysiology’ (patho=suffering, physiology=study of normal function). Pathophysiology, thus, includes study of disordered function (i.e. physiological changes) and breakdown of homeostasis in diseases (i.e. biochemical changes). Pathologists contribute in patient management by providing final diagnosis of disease. Therefore, knowledge and understanding of pathology is essential for all would be practitioners of art of healing and science because unless they have knowledge and understanding of the language and pathologic basis of diseases, they would not be able to institute appropriate treatment or suggest preventive measures to the patient.
For the student of any stream of medical science, the discipline of pathology forms a vital bridge between initial learning phase of preclinical sciences and the final phase of clinical subjects. The role and significance of learning of pathology in clinical medicine is quite well summed up by Sir William Osler (1849–1919), acclaimed physician and teacher in medicine considered as ‘Father of Modern Medicine’, by his famous quote “your practice of medicine will be as good as is your understanding of pathology” (Fig. 1.1).
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Figure 1.1: Sir William Osler (1849–1919). Canadian physician and one of the four founding Professors of Johns Hopkins Hospital, Baltimore, US, is regarded as ‘Father of Modern Medicine’, Sir Osler had keen interest in pathology, was an acclaimed teacher and is also remembered for his famous quotations.
Before there were humans on earth, there was disease, albeit in early animals. Since pathology is the study of disease, then what is disease? In simple language, disease is opposite of health i.e. what is not healthy is disease. Health may be defined as a condition when the individual is in complete accord with the surroundings, while disease is loss of ease (or comfort) to the body (i.e. dis+ease). However, it must be borne in mind that in health there is a wide range of ‘normality’ in various parameters e.g. in height, weight, blood and tissue chemical composition etc. It also needs to be appreciated that at cellular level, the cells display wide range of activities within the broad area of health similar to what is seen in diseased cells. Thus, a disease or an illness means a condition marked by pronounced deviation from the normal healthy state. The term syndrome (meaning running together) is used for a combination of several clinical features caused by altered physiologic processes.
It is important for a beginner in pathology to be familiar with the language used in pathology (Fig.1.2):
  • Patient is the person affected by disease.
  • Lesions are the characteristic changes in tissues and cells produced by disease in an individual or an experimental animal.
  • Pathologic changes or morphology consist of examination of diseased tissues. These can be recognised with the naked eye (gross or macroscopic changes) or studied by microscopic examination of tissues.
  • Causal factors responsible for the lesions are included in etiology of disease (i.e. ‘why’ of disease).
  • Mechanism by which the lesions are produced is termed pathogenesis of disease (i.e. ‘how’ of disease).
  • Functional implications of the lesion felt by the patient are symptoms, and those discovered by the clinician by examination are the physical signs.
  • Clinical significance of the morphologic and functional changes together with results of other investigations help to arrive at an answer to what is wrong (diagnosis), what is going to happen (prognosis), what can be done about it (treatment), and finally what should be done to avoid complications and spread (prevention) (i.e. ‘what’ of disease).
Pathology as the scientific study of disease processes has its deep roots in medical history. Since the beginning of mankind, there has been desire as well as need to know more about the causes, mechanisms and nature of diseases. The answers to these questions have evolved over the centuries—from supernatural beliefs to the present state of our knowledge of modern pathology. However, pathology owes its development to interaction and interdependence on advances in diverse neighbouring branches of science, in addition to the strides made in medical technology. As we shall see in the pages that follow, pathology has evolved over the years as a distinct discipline from anatomy, medicine and surgery, in that sequence.3
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Figure 1.2: Diagrammatic depiction of disease and various terms used in pathology.
Present-day knowledge of primitive culture which was prevalent in the world in prehistoric times reveals that religion, magic and medical treatment were quite linked to each other in those times. The earliest concept of disease understood by the patient and the healer was the religious belief that disease was the outcome of ‘curse from God’ or the belief in magic that the affliction had supernatural origin from ‘evil eye of spirits.’ To ward them off, priests through prayers and sacrifices, and magicians by magic power, used to act as faith-healers and invoke supernatural powers and please the gods. Remnants of ancient superstitions still exist in some parts of the world. The link between medicine and religion became so firmly established throughout the world that different societies had their gods and goddesses of healing; for example: mythological Greeks had Aesculapius and Apollo as the principal gods of healing, Dhanvantri as the deity of medicine in India.
The insignia of healing, the Caduceus, having snake and staff, is believed to represent the god Hermes or Mercury, which according to Greek mythology has power of healing since snake has regenerative powers expressed by its periodic sloughing of its skin. God of Greek medicine, Aesculapius, performed his functions with a staff having a single serpent wound around it. Later (around AD 1800), however, the Caduceus got replaced with twin-serpents wound around a staff topped by a round knob and flanked by two wings and now represents the symbol of medicine (Fig. 1.3).
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Figure 1.3: The Caduceus, representing symbol of medicine, is the traditional symbol of god Hermes or Mercury. It features twin serpents winding around a winged staff.
The period of ancient religious and magical beliefs was followed by the philosophical and rational approach to disease by the methods of observations. This happened at the time when great Greek philosophers—Socrates, Plato and Aristotle, introduced philosophical concepts to all natural phenomena.
But the real practice of medicine began with Hippocrates (460–370 BC), the great Greek clinical genius of all times and regarded as ‘the father of medicine’ (Fig. 1.4). Hippocrates dissociated medicine from religion and magic. Instead, he firmly believed in study of patient’s symptoms and described methods of diagnosis. He recorded his observations on cases in the form of collections of writings called Hippocratic Corpus which remained the mainstay of learning of medicine for nearly two thousand years. Hippocrates followed rational and ethical attitudes in practice and teaching of medicine and is revered by the medical profession by taking ‘Hippocratic oath’ at the time of entry into practice of medicine.
After Hippocrates, Greek medicine reached Rome (Italy) which controlled Greek world after 146 BC and, therefore, it dominated the field of development of medicine in ancient Europe then. In fact, since old times, many tongue twisting terminologies in medicine have their origin from Latin language which was the official language of countries included in ancient Roman Empire (Spanish, Portuguese, Italian, French and Greek languages have their origin from Latin).
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Figure 1.4: Hippocrates (460–370 BC). The great Greek clinical genius and regarded as ‘the Father of Medicine’. He introduced ethical aspects to medicine.
4In Rome, Hippocratic teaching was propagated by Roman physicians, notably by Cornelius Celsus (53 BC-7 AD) and Claudius Galen (130–200 AD). Celsus first described four cardinal signs of inflammation—rubor (redness), tumor (swelling), calor (heat), and dolor (pain). Galen postulated humoral theory, later called Galenic theory. This theory suggested that the illness resulted from imbalance between four humors (or body fluids): blood, lymph, black bile (believed at that time to be from the spleen), and biliary secretion from the liver.
The hypothesis of disequilibrium of four elements constituting the body (Dhatus) similar to Hippocratic doctrine finds mention in ancient Indian medicine books compiled about 200 AD—Charaka Samhita, a finest document by Charaka on medicine listing 500 remedies, and Sushruta Samhita, similar book of surgical sciences by Sushruta, and includes about 700 plant-derived medicines.
The end of Medieval period was marked by backward steps in medicine. There were widespread and devastating epidemics which reversed the process of rational thinking again to supernatural concepts and divine punishment for ‘sins.’ The dominant belief during this period was that life was due to influence of vital substance under the control of soul (theory of vitalism).
The backwardness of Medieval period was followed by the Renaissance period, i.e. revival of learning. The Renaissance began from Italy in late 15th century and spread to whole of Europe. During this period, there was quest for advances in art and science.
The beginning of the development of human anatomy took place during this period with the art works and drawings of human muscles and embryos by famous Italian painter Leonardo da Vinci (1452–1519). Dissection of human body was started by Vesalius (1514–1564) on freshly executed criminals. His pupils further popularised the practice of human anatomic dissection for which special postmortem amphitheatres came in to existence in various parts of ancient Europe.
Antony van Leeuwenhoek (1632–1723), a cloth merchant by profession in Holland, during his spare time invented the first ever microscope by grinding the lenses himself through which he recognised male spermatozoa and also introduced histological staining in 1714 using saffron to examine muscle fibres.
Marcello Malpighi (1624–1694) used microscope extensively and observed the presence of capillaries and described the malpighian layer of the skin, and lymphoid tissue in the spleen (malpighian corpuscles). Malpighi is known as ‘the father of histology.’
The credit for beginning of the study of morbid anatomy (pathologic anatomy) goes to Italian anatomist-pathologist, Giovanni B. Morgagni (1682–1771). By his work, Morgagni demolished the ancient humoral theory of disease and published his life-time experiences based on 700 postmortems and their corresponding clinical findings. He, thus, laid the foundations of clinicopathologic methodology in the study of disease and introduced the concept of clinicopathologic correlation (CPC), establishing a coherent sequence of cause, lesions, symptoms, and outcome of disease.
Sir Percivall Pott (1714–1788), famous surgeon in England, described arthritic tuberculosis of the spine (Pott’s disease) and identified the first ever occupational cancer (cancer of scrotal skin) in the chimney sweeps in 1775 and discovered chimney soot as the first carcinogenic agent. The study of anatomy in England during the latter part of 18th Century was dominated by the two Hunter brothers. These were John Hunter (1728–1793), a student of Sir Percivall Pott, who rose to become the greatest surgeon-anatomist of all times and his elder brother William Hunter (1718–1788) who was a reputed anatomist-obstetrician. These brothers together started the first ever museum by collection of surgical specimens from their flourishing practice, which came to be known as the Hunterian Museum, now housed in Royal College of Surgeons of London. Among many pupils of John Hunter was Edward Jenner (1749–1823) whose work on inoculation in smallpox is well known. The era of gross pathology had three more illustrious and brilliant physician-pathologists in England who were colleagues at Guy’s Hospital in London:
  • Richard Bright (1789–1858) who described non-suppurative nephritis, later termed glomerulonephritis or Bright’s disease;
  • Thomas Addison (1793–1860) who gave an account of chronic adrenocortical insufficiency termed Addison’s disease; and
  • Thomas Hodgkin (1798–1866), who observed the complex of chronic enlargement of lymph nodes, often with enlargement of the liver and spleen, later called Hodgkin’s disease.
R.T.H. Laennec (1781–1826), a French physician, dominated the early part of 19th century by his numerous discoveries. He described several lung diseases (tubercles, caseouslesions, miliary lesions, pleural effusion, and bron chiectasis), chronic sclerotic liver disease (later called Laennec’s cirrhosis) and invented stethoscope.
Morbid anatomy attained its zenith with appearance of Carl F. von Rokitansky (1804–1878), self-taught German pathologist who performed nearly 30,000 autopsies himself and described acute yellow atrophy of the liver, wrote an outstanding monograph on diseases of arteries and congenital heart defects.
Up to middle of the 19th century, correlation of clinical manifestations of disease with gross pathological findings 5at autopsy became the major method of study of disease. Sophistication in surgery led to advancement in pathology. The anatomist-surgeons of earlier centuries got replaced largely with surgeon-pathologists in the 19th century.
Pathology started developing as a diagnostic discipline in later half of the 19th century with the evolution of cellular pathology which was closely linked to technological advancements in machinery manufacture for cutting thin sections of tissue, improvement in microscope, and development of chemical industry and dyes for staining.
The discovery of existence of disease-causing microorganisms was made by French chemist Louis Pasteur (1822–1895), thus demolishing the prevailing theory of spontaneous generation of disease and firmly established germ theory of disease. Subsequently, G.H.A. Hansen (1841–1912) in Germany identified Hansen’s bacillus in 1873 as the first microbe causative for leprosy (Hansen’s disease). While the study of infectious diseases was being made, the concept of immune tolerance and allergy emerged which formed the basis of immunisation initiated by Edward Jenner.
Developments in chemical industry helped in switch over from earlier dyes of plant and animal origin to synthetic dyes; aniline violet being the first such synthetic dye in 1856. This led to emergence of a viable dye industry for histological and bacteriological purposes. The impetus for the flourishing and successful dye industry came from the works of numerous pioneers as under:
  • Paul Ehrlich (1854–1915), German physician, conferred Nobel Prize in 1908 for his work in immunology, described Ehrlich’s test for urobilinogen using Ehrlich’s aldehyde reagent, staining techniques of cells and bacteria, and laid the foundations of clinical pathology.
  • Christian Gram (1853–1938), Danish physician, developed bacteriologic staining by crystal violet.
  • D.L. Romanowsky (1861–1921), Russian physician, developed stain for peripheral blood film using eosin and methylene blue derivatives.
  • Robert Koch (1843–1910), German bacteriologist, besides Koch’s postulate and Koch’s phenomena, developed techniques of fixation and staining for identification of bacteria, discovered tubercle bacilli in 1882 and cholera vibrio organism in 1883.
  • May-Grünwald in 1902 and Giemsa in 1914 developed blood stains and applied them for classification of blood cells and bone marrow cells.
  • Sir William Leishman (1865–1926) described Leishman’s stain for blood films in 1914 and observed Leishman-Donovan bodies (LD bodies) in leishmaniasis.
Simultaneous technological advances in machinery manufacture led to development and upgrading of microtomes for obtaining thin sections of organs and tissues for staining by dyes for enhancing detailed study of sections.
Rudolf Virchow (1821–1905) in Germany is credited with the beginning of microscopic examination of diseased tissue at cellular level and thus began histopathology as a method of investigation. Virchow hypothesised cellular theory having following two components:
  • All cells come from other cells.
  • Disease is an alteration of normal structure and function of these cells.
Virchow was revered as the Pope of pathology in Europe and is aptly known as the ‘father of cellular pathology’ (Fig. 1.5). Thus, sound foundation of diagnostic pathology based on microscopy had been laid which was followed and promoted by numerous brilliant successive workers. This gave birth to biopsy pathology and thus emerged the discipline of surgical pathology. Virchow also described etiology of embolism (Virchow’s triad—slowing of blood-stream, changes in the vessel wall, changes in the blood itself), metastatic spread of tumours (Virchow’s lymph node), and components and diseases of blood (fibrinogen, leukocytosis, leukaemia).
A few other landmarks in further evolution of modern pathology in this era are as follows:
  • Karl Landsteiner (1863–1943) described the existence of major human blood groups in 1900 and is considered “father of blood transfusion”; he was awarded Nobel Prize in 1930.
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    Figure 1.5: Rudolf Virchow (1821–1905). German pathologist who proposed cellular theory of disease and initiated biopsy pathology for diagnosis of diseases and is known as ‘the Father of Cellular Pathology’.
  • Ruska and Lorries in 1933 developed electron microscope which aided the pathologist to view ultrastructure of cell and its organelles.
  • The development of exfoliative cytology for early detection of cervical cancer began with George N. Papanicolaou (1883–1962), a Greek-born, American pathologist, in 1930s and is known as ‘father of exfoliative cytology’ (Fig. 1.6).
Another pioneering contribution in pathology in the 20th century was by an eminent teacher-author, William Boyd (1885–1979), psychiatrist-turned pathologist, whose textbooks—’Pathology for Surgeons’ (first edition 1925) and ‘Textbook of Pathology’ (first edition 1932), dominated and inspired the students of pathology all over the world for a few generations due to his flowery language and lucid style.
The strides made in the latter half of 20th century until recent times in 21st century have made it possible to study diseases at genetic and molecular level, and provide an evidencebased and objective diagnosis that may enable the physician to institute targeted therapy. The major impact of advances in molecular biology are in the field of diagnosis and treatment of genetic disorders, immunology and in cancer. Some of the revolutionary discoveries during this time are as under (Fig. 1.7):
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Figure 1.6: George N Papanicolaou (1883–1962). An American pathologist, who developed Pap test for diagnosis of cancer of uterine cervix and is known as ‘the Father of Exfoliative Cytology’.
  • Description of the structure of DNA of the cell by Watson and Crickin 1953.
  • Identification of chromosomes and their correct number in humans (46) by Tijo and Levan in 1956.
  • Identification of Philadelphia chromosome in chronic myeloid leukaemia by Nowell and Hagerford in 1960 as the first chromosomal abnormality in any cancer.
  • In Situ hybridization (ISH) introduced in 1969 in which a labelled probe is employed to detect and localise specific RNA or DNA sequences ‘in situ’ (i.e. in the original place). Its later modification employs use of fluorescence microscopy (FISH) to detect specific localisation of the defect on chromosomes.
  • Recombinant DNA technique developed in 1972 using restriction enzymes to cut and paste bits of DNA.
  • Introduction of polymerase chain reaction (PCR) i.e. “xeroxing” of DNA fragments by Kary Mullis in 1983 has revolutionised the diagnostic molecular genetics. PCR analysis is more rapid than ISH, can be automated by thermal cyclers and requires much lower amount of starting DNA.
  • Invention of flexibility and dynamism of DNA by Barbara McClintock for which she was awarded Nobel Prize in 1983.
  • Mammalian cloning started in 1997 by Ian Wilmut and his colleagues at Roslin Institute in Edinburgh, by successfully using a technique of somatic cell nuclear transfer to create the clone of a sheep named Dolly. Human reproductive cloning, however, is very risky, besides being absolutely unethical.
  • The era of stem cell research started in 21st century by harvesting these primitive cells isolated from embryos and maintaining their growth in the laboratory. There are 2 types of sources of stem cells in humans: embryonic stem cells and adult stem cells, the former being more numerous. Stem cells are seen by many researchers as having virtually unlimited applications in the treatment of many human diseases such as Alzheimer’s disease, diabetes, cancer, strokes, etc. At some point of time, stem cell therapy may be able to replace whole organ transplant and instead stem cells ‘harvested’ from the embryo may be used.
  • Human Genome Project (HGP) consisting of a consortium of countries was completed in April 2003 coinciding with 50 years of description of DNA double helix by Watson and Crick in April 1953. The sequencing of human genome reveals that human genome contains approximately 3 billion base pairs of amino acids, which are located in the 23 pairs of chromosomes within the nucleus of each human cell. Each chromosome contains an estimated 30,000 genes in the human genome which carry the instructions for making proteins. The HGP has given us the ability to read nature’s complete genetic blueprint used in making of each human being (i.e. gene mapping). Clinical trials by gene therapy on treatment of some single gene defects have resulted in some success, especially in haematological and immunological diseases.
7Future developments in genetic engineering may result in designing new and highly effective individualised treatment options for genetic diseases as well as suggest prevention against diseases.
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Figure 1.7: Molecular structure of human chromosome
Telepathology is defined as the practice of diagnostic pathology by a remote pathologist utilising images of tissue specimens transmitted over a telecommunication network. Depending upon need and budget, telepathology system is of two types:
Static (store-and-forward, passive telepathology) In this, selected images are captured, stored and then transmitted over the internet via e-mail attachment, file transfer protocol, web page or CD-ROM. It is quite inexpensive and is more common but suffers from disadvantage of having sender’s bias in selection of transmitted images.
Dynamic (Robotic interactive telepathology) Here, the images are transmitted in real-time from a remote microscope. Robotic movement of stage of microscope is controlled remotely and the desired images and fields are accessioned from a remote/local server. Thus, it almost duplicates to perfection the examination of actual slides under the microscope, hence is referred to as Virtual Microscopy. However, image quality and speed of internet can be major hurdles.
Human pathology is conventionally studied under two broad divisions: General Pathology dealing with general principles of disease, and Systemic Pathology that includes study of diseases pertaining to the specific organs and body systems. Diagnostic pathology, however, involves morphological and non-morphological disciplines of laboratory sciences as follows:
These branches essentially involve application of microscope as an essential tool for the study and include histopathology, cytopathology and haematology.
A. HISTOPATHOLOGY Histopathology, used synonymously with anatomic pathology, pathologic anatomy, morbid anatomy, or tissue pathology, is the classic method of study and still the most useful one which has stood the test of time. The study includes structural changes observed by naked eye examination referred to as gross or macroscopic changes, and the changes detected by microscopy, which may be further supported by numerous special staining methods such as histochemistry and immunohistochemistry to arrive at the most accurate diagnosis. In modern times, anatomic pathology includes sub-specialities such as cardiac pathology, pulmonary pathology, neuropathology, renal pathology, gynaecologic pathology, breast pathology, dermatopathology, gastrointestinal pathology, oral pathology, and so on. Anatomic pathology includes the following subdivisions:
  1. Surgical pathology It deals with the study of tissues removed from the living body by biopsy or surgical resection. Surgical pathology constitutes the bulk of work for the pathologist and includes study of tissue by conventional paraffin embedding technique; intraoperative frozen section may be employed for rapid diagnosis.
  2. Experimental pathology This is defined as production of disease in the experimental animal and study of morphological changes in organs after sacrificing the animal.8
  3. Forensic pathology and autopsy work This includes the study of organs and tissues removed at postmortem for medicolegal work and for determining the underlying sequence and cause of death. By this, the pathologist attempts to reconstruct the course of events how they may have happened in the patient during life which culminated in his death. Postmortem anatomical diagnosis is helpful to the clinician to enhance his knowledge about the disease and his judgement while forensic autopsy is helpful for medicolegal purposes. The significance of a careful postmortem examination is appropriately summed up in the old saying ‘the dead teach the living’.
  1. CYTOPATHOLOGY Though a branch of anatomic pathology, cytopathology has developed as a distinct subspeciality in recent times. It includes study of cells shed off from the lesions (exfoliative cytology) and fine-needle aspiration cytology (FNAC) of superficial and deep-seated lesions for diagnosis.
  2. HAEMATOLOGY Haematology deals with the diseases of blood. It includes laboratory haematology and clinical haematology; the latter covers the management of patient as well.
These include clinical pathology, clinical biochemistry, microbiology, immunology, genetics and molecular pathology. In these diagnostic branches, qualitative, semi-quantitative or quantitative determinations are carried out in the laboratory, while microscope may be required for only some of these lab tests.
  1. CLINICAL PATHOLOGY Analysis of various fluids including blood, urine, semen, CSF and other body fluids is included in this branch of pathology. Such analysis may be qualitative, semi-quantitative or quantitative.
  2. CLINICAL BIOCHEMISTRY Quantitative determination of various biochemical constituents in serum and plasma, and in other body fluids is included in clinical biochemistry.
  3. MICROBIOLOGY This is study of disease-causing microbes implicated in human diseases. Depending upon the type of microorganims studied, it has further developed into such as bacteriology, parasitology, mycology, virology etc.
  4. IMMUNOLOGY Detection of abnormalities in the immune system of the body comprises immunology and immunopathology.
  5. MEDICAL GENETICS This is the branch of human genetics that deals with the relationship between heredity and disease. There have been important developments in the field of medical genetics e.g. in blood groups, inborn errors of metabolism, chromosomal aberrations in congenital malformations and neoplasms etc.
  6. MOLECULAR PATHOLOGY The detection and diagnosis of abnormalities at the level of DNA of the cell is included in molecular pathology such as in situ hybridisation, PCR etc. These methods are now not only used for research purposes but are also being used as a part of diagnostic pathology reports.
The above divisions of pathology into several subspecialities are quite artificial since overlapping of disciplines is likely, ultimate aim of pathologist being to establish the final diagnosis and learn the causes and mechanisms of disease.