1
Introduction to Pathology

S. R. Prabhu1 and Suja Pillai2

1 School of Dentistry, University of Queensland, Brisbane, Queensland, Australia

2 Faculty of Medicine, University of Queensland, Brisbane, Queensland, Australia

1.1 Introduction

Pathology is the medical speciality concerned with the scientific study of the nature and causes of diseases. It bridges science and medicine and supports every aspect of patient care, from diagnostic testing, treatment and advice to disease prevention. The origin of the term (etymology) ‘pathology’ is derived from the Greek words ‘Pathos’ and ‘logy’, meaning the study of suffering (1). ‘Disease’ refers to a definable deviation from normal phenotypic observable characteristics evident via patient symptoms and signs (2). The cause of the disease is referred to as its aetiology. One disease entity can have more than one aetiology, and it is also possible that one aetiology can lead to more than one disease. Sometimes, the affix pathy indicates a disease state in both physical ailments, such as cardiomyopathy, and psychological conditions, such as psychopathy (3). Each disease develops through physical, chemical and cellular events. This stepwise process of disease development is called its pathogenesis – a Greek word meaning generation of suffering (2). It leads to cellular and tissue function changes. A pathologist is a specialist in pathology who offers diagnosis using observations at the clinical, gross, body fluid, light microscopic, immunophenotypic, ultrastructural, cytogenetic and molecular levels (4). Pathologists diagnose disease by generating a differential diagnosis and then finding the best fit for the clinical presentation, the radiographic appearance and the pathologic (clinical lab and morphologic) findings (2). The presentation of a disease to a clinician is in the form of a human patient with variably specific complaints (symptoms).

1.2 History of Pathology

Pathology has evolved over the years as a distinct discipline. Its roots arise in pre‐historic and medieval times. The earliest concept of disease was the religious belief that disease was the outcome of a ‘curse from God’ or the belief that it had a supernatural cause from the ‘evil eye of spirits’ (5). The rational approach to disease by methods of observation followed after many decades. Gross features of the disease that were directly visible, either in the living or dead, came first to notice, and documentation of the disease began with Egyptian medicine. In the last three centuries BC, the Greeks, heavily influenced by Hippocrates, made lasting contributions to anatomy and pathology (6). Hippocrates (460–370 BC) is traditionally considered ‘the father of medicine’. He disassociated disease from religion and magic. He believed in studying patients’ symptoms and described methods of diagnosis (6). His collection of writings based on observations of cases called the Hippocratic Corpus was the mainstay of learning medicine for over two thousand years. In Rome, Hippocratic teaching was promoted by Cornelius Celsus (53 BC–7 AD) and Claudius Galen (130–200 AD) (6). Celsius was the first to describe the following four cardinal signs of inflammation: rubor, tumour, calor and dolor (6). In addition, Galen postulated humoral theory (Galenic theory). According to this theory, an imbalance of four body fluids – blood, lymph, biliary secretion from the liver and bile, which was believed at that time to be from the spleen – resulted in illness (6).

Human anatomy and gross pathology became popular during the Renaissance (14–17th century). During this period, anatomic dissections were performed in various theatres in ancient parts of Europe. Correlations of clinical manifestations of disease with gross pathological findings at autopsies became the major method of study of pathology until the middle of the 17th century. Before 1668, Antony van Leeuwenhoek (1632–1723) (6, 7), a cloth merchant in Holland, invented the first‐ever hand‐held microscope by grinding the lenses. He recognised male spermatozoa using his microscope and introduced staining using saffron to examine muscle fibres (6, 7). Other prominent individuals of this period who contributed to the development of pathology include Marcello Malpighi (1624–1694), Giovanni B Morgagni (1682–1771), Sir Percival Pott (1714–1788), John Hunter (1728–1793), William Hunter (1718–1788), Edward Jenner (1749–1823), Thomas Addison (1793–1860), Thomas Hodgkin (1798–1866) and RTH Laennec (1781–1826) (6–10).

Pathology started developing in the latter half of the 19th century. Rudolf Ludwig Carl Virchow (1821–1902), a German physician and pathologist, is known as ‘the father of modern pathology’ (8, 9). Virchow was the first to develop a systematic autopsy method based on his knowledge of cellular pathology (10). Virchow is also credited with several fundamental discoveries. His most widely known scientific contribution is his cell theory. Virchow was the first to analyse hair in criminal investigations and made the first forensic report in 1861 (11, 12).

During the 19th century, many other individuals contributed to pathology. They include Louis Pasteur (1822–1895) (13) and G H A Hansen (1841–1912) (14), who were responsible for discovering causative microorganisms for tuberculosis and leprosy, respectively (14). Other prominent individuals who contributed to pathology during this period were Paul Ehrlich (1854–1915) (13), Christian Gram (1853–1938), D L Romanowsky (1861–1921), Robert Koch (1843–1910), Sir William Leishman (1865–1926), Karl Landsteiner (1863–1943) and G N Papanicolaou (1883–1962) (6). In addition, Joe Hin Tejo and Albert Levan (1956) identified chromosomes and their correct number in humans (6). Other significant milestones in the development of modern pathology include the identification of the Philadelphia chromosome in leukaemia in 1960, the introduction of the in situ hybridisation technique in 1969, the recombinant DNA technique in 1974 and the polymerase chain reaction (PCR) in 1983. In situ hybridisation was invented in 1969 by American biologists (15). Recombinant DNA technology was created in 1974 by Stanley Cohen of Stanford and Herbert Boyer of UCSF (16).

1.3 Study of Pathology

Pathology is best studied in two stages: general pathology and systematic pathology.

1.3.1 General Pathology

General pathology is the foundation of pathology. The broad scientific field seeks to understand the mechanisms of injury to cells and tissues and how to respond to and repair injury. Areas of study include cellular adaptation to injury, necrosis, inflammation, wound healing and neoplasia. General pathology covers basic knowledge that has to be acquired before studying systemic pathology (17).

1.3.2 Systematic Pathology (Systemic Pathology)

Systematic pathology deals with descriptions of diseases affecting organs or organ systems. Some pathologists discuss these diseases under the heading of systemic pathology. In recent years, however, the term systemic has been abandoned by many pathologists because the word ‘systemic’ refers to a disease that has spread to all body systems. The preferred term for the study of organ‐based pathology, therefore, is systematic pathology.

1.4 Specialities and Subspecialties of Pathology

1.4.1 Anatomical Pathology

Anatomical pathology is a medical speciality concerned with diagnosing disease based on the gross, microscopic, chemical, immunologic and molecular examination of organs, tissues and the whole body (autopsy). Anatomic pathology has two subdivisions: histopathology and cytopathology (17).

The pathology laboratory receives large whole organs, or parts of organs, removed during surgery. These specimens are examined for size, shape, colour and external abnormalities (gross pathology) (Figure 1.1a). The initial step in reviewing a clinical specimen is confirmation of the identity of the patient and the anatomical site from which the sample was obtained. Next, the clinical team should communicate sufficient clinical data to the pathology team to guide the appropriate diagnostic examination and interpretation of the specimen. After recording these findings, smaller samples are taken for definitive microscopic evaluation. Surgical pathology allows for a definitive diagnosis of the disease. This is usually performed by a combination of gross (Figure 1.1a) and histopathologic (Figure 1.1b) examinations of the tissue and may involve evaluations of molecular properties of the tissue by immunohistochemistry or other laboratory tests.

Figure 1.1 Ameloblastoma of the mandible. Gross pathology of a surgical specimen (a) and histopathologic features (b).

Source: With permission of WebPathology,...