A renal cell carcinoma (chromophobe type) viewed on auhematoxylin & eosin stained slide
Pathology is the scientific study of the nature, causes, processes, development, and consequences of the diseases.
Pathology addresses four components of disease:
- mechanisms of development (pathogenesis)
- structural alterations of cells (morphologic changes)
- the consequences of changes (clinical manifestations)
Pathology is further separated into divisions, based on either the system being studied (e.g. veterinary pathology and animal disease) or the focus of the examination (e.g. forensic pathology and determining the cause of death).
History of pathology:The history of pathology can be traced back to antiquity when people began examining bodies. The examination of bodies led to the dissection of bodies in order to justify the cause of death. During that time, the people already began formulating today what we know as inflammation, tumors, boils, and much more.
Pathology began to develop as a subject during the 19th Century through teachers and physicians that studied pathology. They referred to it as “pathological anatomy” or “morbid anatomy.” However, pathology as a field of medicine was not recognized until the late 19th and early 20th centuries. In the 19th century, physicians realized that disease-causing pathogens, germs, created themselves and that symptoms were not the vital characteristics of a disease. Through the new information gathered regarding germ reproduction, physicians began to compare the characteristics of one germ’s symptoms as they developed within an affected individual to another germ’s characteristics and symptoms.
This realization led to the foundational understanding that diseases are able to create themselves, and that they can affect human beings in unique ways. In order to determine causes of diseases, medical experts used the most common and widely accepted assumptions or symptoms of their times. This is true for those in the past and today.
What set pathology apart from other specialties was the ability to determine a symptom with the naked eye. During the 19th century, Rudolf Virchow gave the biggest contribution to the field by introducing the procedure of analyzing tissue and cells through a microscope to pathologists. This greatly affected the discipline because it was another way to analyze objects, and it led to more advanced technological developments.
By the late 1920s to early 1930s pathology was deemed a medical specialty. During the years following, the decision to split pathology into sub-specialties arose. Today, anatomical, clinical, molecular, plant, forensic, oral, veterinary, dermatopathology, hematopathology, and pathology exist as medical specialties. Today, pathologists are discovering new diseases, examining exotic diseases that enter the country, and working on a solution to cure diseases such as AIDS, HIV, Herpes, cancer, and more. Thus the evolution of pathology is evidence of the real value of science, which lies in its ability to continually research and develop new methods while giving credit to those who originally developed the idea.
Pathologist instructor and students of anatomical pathology
Anatomical pathology (Commonwealth) or anatomic pathology (United States) is a medical specialty that is concerned with the diagnosis of disease based on the gross, microscopic, chemical, immunologic and molecular examination of organs, tissues, and whole bodies (autopsy).
Anatomical pathology is itself divided in subspecialties, the main ones being surgical pathology, cytopathology, and forensic pathology. To be licensed to practice pathology, one has to complete medical school and secure a license to practice medicine. An approved residency program and certification (in the United States, the American Board of Pathology or the American Osteopathic Board of Pathology) is usually required to obtain employment or hospital privileges.
Anatomical pathology is one of two branches of pathology, the other being clinical pathology, the diagnosis of disease through the laboratory analysis of bodily fluids and tissues. Often, pathologists practice both anatomical and clinical pathology, a combination known as general pathology. The distinction between anatomic and clinical pathology is increasingly blurred by the introduction of technologies that require new expertise and the need to provide patients and referring physicians with integrated diagnostic reports. Similar specialties exist in veterinary pathology.
Clinical chemistry: an automated blood chemistry analyzer
Clinical pathology is a medical specialty that is concerned with the diagnosis of disease based on the laboratory analysis of bodily fluids such as blood and urine, and tissues using the tools of chemistry, microbiology, hematology and molecular pathology. Clinical pathologists work in close collaboration with medical technologists, hospital administrations, and referring physicians to ensure the accuracy and optimal utilization of laboratory testing.
Clinical pathology is one of the two major divisions of pathology, the other being anatomical pathology. Often, pathologists practice both anatomical and clinical pathology, a combination sometimes known as general pathology.
Dermatopathology:Dermatopathology is a subspecialty of anatomic pathology that focuses on the skin as an organ. It is unique in that there are two routes which a physician can use to obtain this specialization. All general pathologists and general dermatologists are trained in the pathology of the skin; however, the dermatopathologist is a specialist in this organ. In the USA, either a general pathologist or a dermatologist can undergo a 1 to 2 year fellowship in the field of dermatopathology. The completion of this fellowship allows one to take a subspecialty board examination, and becomes a board certified dermatopathologist.
Hematopathology: A Wright's stained bone marrow aspirate smear of patient with precursor B-cell acutelymphoblastic leukemia
Hematopathology is the study of diseases of blood cells (White blood cells, red blood cells, platelets) and cells/tissues/organs comprising the hematopoietic system. The term hematopoietic system refers to tissues and organs that produce and/or primarily host hematopoietic cells and include bone marrow, lymph node, thymus, spleen, and other lymphoid tissues. In the United States, hematopathology is a board certified subspecialty (American Board of Pathology) practiced by those physicians who have completed general pathology residency (anatomic, clinical, or combined) and an additional year of fellowship training in hematology. The hematopathologist reviews biopsies of lymph nodes, bone marrows and other tissues involved by an infiltrate of cells of the hematopoietic system. In addition, the hematopathologist may be in charge of flow cytometric and/or molecular hematopathology studies. After the hematopathologist makes the diagnosis, the hematologist or hemato-oncologist can make a decision about the best course of action.
Classification and external resources
Micrograph of membranous nephropathy showing prominent glomerular basement membrane spikes. MPAS stain
Renal pathology is the study of medial diseases (non-tumor) of the kidney. In the United States, renal pathology is practiced by physicians who have completed general pathology residency training (anatomic or combined anatomic/clinical) and an additional year of fellowship training in renal pathology. A renal pathologist reviews biopsies of the kidney and integrates findings from multiple methodologies including light microscopy, immunofluorescence microscopy, and electron microscopy. Renal pathologists work closely with nephrologists and carefully integrate the clinical history/laboratory studies in the evaluation of renal biopsy specimens. Renal pathologists require a detailed understanding of immunology as it is often critical in interpreting specimens (particularly from renal transplants) as well as conceptualizing pathogenesis of many renal diseases. Once a morphologic diagnosis is made by a renal pathologist, the diagnosis is communicated to the clinical physician (nephrologist) who can then formulate a plan of care/treatment.
Oral and Maxillofacial Pathology:Oral and Maxillofacial Pathology is one of nine dental specialties recognized by the American Dental Association. Oral Pathologists must complete three years of post doctoral training in an accredited program and subsequently obtain Diplomate status from the American Board of Oral and Maxillofacial Pathology. The specialty focuses on the diagnosis, clinical management and investigation of diseases that affect the oral cavity and surrounding maxillofacial structures including but not limited to odontogenic, infectious, epithelial, salivary gland, bone and soft tissue pathologies.
Forensic pathology:Forensic pathology is a branch of pathology concerned with determining the cause of death by examination of a cadaver. The autopsy is performed by the pathologist at the request of a coroner usually during the investigation of criminal law cases and civil law cases in some jurisdictions. Forensic pathologists are also frequently asked to confirm the identity of a cadaver.
The word forensics is derived from the Latin forēnsis meaning forum.
Veterinary pathology:Veterinary pathologists are doctors of veterinary medicine who specialize in the diagnosis of diseases through the examination of animal tissue and body fluids. As with medical pathology, veterinary pathology is divided in two branches, anatomical pathology and clinical pathology.
Veterinary pathologists are also critical participants in the drug discovery and development. Drug discovery is most often accomplished by testing for efficacy in animal models of disease such as arthritis. Drug discovery involves modification of chemical molecules to improve their biological characteristics of absorption, distribution, metabolism and elimination (ADME) where veterinary toxicologic pathologists evaluate new candidate drugs for toxic effects in animals before they are tested on humans.
Powdery mildew, a biotrophic fungus
Plant pathology (also phytopathology) is the scientific study of plant diseases caused by pathogens (infectious diseases) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomycetes, bacteria, viruses, viroids, virus-like organisms, phytoplasmas, protozoa, nematodes and parasitic plants. Not included are insects, mites, vertebrate or other pests that affect plant health by consumption of plant tissues. Plant pathology also involves the study of pathogen identification, disease etiology, disease cycles, economic impact, plant disease epidemiology, plant disease resistance, how plant diseases affect humans and animals, pathosystem genetics, and management of plant diseases.
The "disease triangle" is a central concept of plant pathology. It is based on the principle that infectious diseases develop, or do not develop, based on three-way interactions between the host, the pathogen, and environmental conditions. Pathology is the medical specialty concerned with the study of the nature and causes of diseases. It underpins every aspect of medicine, from diagnostic testing and monitoring of chronic diseases to cutting-edge genetic research and blood transfusion technologies. Pathology is integral to the diagnosis of every cancer.
Pathology plays a vital role across all facets of medicine throughout our lives, from pre-conception to post mortem. In fact it has been said that “Medicine IS Pathology”.
Due to the popularity of many television programs, the word ‘pathology’ conjures images of dead bodies and people in lab coats investigating the cause of suspicious deaths for the police. That’s certainly a side of pathology, but in fact it’s far more likely that pathologists are busy in a hospital clinic or laboratory helping living people.
Pathologists are specialist medical practitioners who study the cause of disease and the ways in which diseases affect our bodies by examining changes in the tissues and in blood and other body fluids. Some of these changes show the potential to develop a disease, while others show its presence, cause or severity or monitor its progress or the effects of treatment.
The doctors you see in surgery or at a clinic all depend on the knowledge, diagnostic skills and advice of pathologists. Whether it’s a GP arranging a blood test or a surgeon wanting to know the nature of the lump removed at operation, the definitive answer is usually provided by a pathologist. Some pathologists also see patients and are involved directly in the day-to-day delivery of patient care.
Currently pathology has nine major areas of activity. These relate to either the methods used or the types of disease which they investigate. For further information on each discipline please click on one of the following:
Anatomical Pathology Chemical Pathology Clinical Pathology Forensic Pathology General Pathology Genetic Pathology Haematology Immunopathology Microbiology
Molecular pathology:Molecular pathology is an emerging discipline within pathology, and focuses in the study and diagnosis of disease through the examination of molecules within organs, tissues or bodily fluids. Molecular pathology shares some aspects of practice with both anatomic pathology and clinical pathology, molecular biology, biochemistry, proteomics and genetics, and is sometimes considered a "crossover" discipline. It is multi-disciplinary in nature and focuses mainly on the sub-microscopic aspects of disease and unknown illnesses with strange causes.
It is a scientific discipline that encompasses the development of molecular and genetic approaches to the diagnosis and classification of human tumors, the design and validation of predictive biomarkers for treatment response and disease progression, the susceptibility of individuals of different genetic constitution to develop cancer, and the environmental and lifestyle factors implicated in carcinogenesis.
General pathology:General pathology is a broad and complex scientific field which covers all of the areas of more specialist pathologies. General pathologists seek to understand the mechanisms of injury to cells and tissues, as well as the body's means of responding to and repairing injury. Areas of study include cellular adaptation to injury, necrosis, inflammation, wound healing and neoplasia. The term "general pathology" is also used to describe the practice of both anatomical and clinical pathology.
Pathology as a medical specialty:
Doctor, Medical Specialist
Doctor of Medicine, Doctor of Osteopathic Medicine
Pathologists are doctors who diagnose and characterize disease in living patients by examining biopsies or bodily fluids. In addition, pathologists interpret medical laboratory tests to help prevent illness or monitor a chronic condition.
The vast majority of cancer diagnoses are made by pathologists. Pathologists examine tissue biopsies to determine if they are benign or cancerous. Some pathologists specialize in genetic testing that can, for example, determine the most appropriate treatment for particular types of cancer. In addition, a pathologist analyzes blood samples from a patient's annual physical and alerts their primary care physician to any changes in their health early, when successful treatment is most likely. Pathologists also review results of tests ordered or performed by specialists, such as blood tests ordered by a cardiologist, a biopsy of a skin lesion removed by a dermatologist, or a Pap test performed by a gynecologist, to detect abnormalities.
This mastectomy specimen contains an infiltrating ductal carcinoma of the breast. A pathologist will use immunohistochemistry and fluorescent in-situ hybridization to detect markers which determine the optimal chemotherapy regimen for this patient.
Pathologists work with other doctors, medical specialty societies, medical laboratory professionals, and health care consumer organizations to set guidelines and standards for medical laboratory testing that help improve a patient's medical care and guide treatment, as well as ensure the quality and safety of domestic and international medical laboratories.
Pathologists may also conduct autopsies to investigate causes of death. Autopsy results can aid living patients by revealing a hereditary disease unknown to a patient's family.
Pathology is a core discipline of medical school and many pathologists are also teachers. As managers of medical laboratories (which include chemistry, microbiology, cytology, the blood bank, etc.), pathologists play an important role in the development of laboratory information systems. Although the medical practice of pathology grew out of the tradition of investigative pathology, most modern pathologists do not perform original research.
Pathology is a unique medical specialty. Pathology touches all of medicine, as diagnosis is the foundation of all patient care. In fact, more than 70 percent of all decisions about diagnosis and treatment, hospital admission, and discharge rest on medical test results.
Pathologists play a critical role on the patient care team, working with other doctors to treat patients and guide care. To be licensed, candidates must complete medical training, an approved residency program, and be certified by an appropriate body. In the US, certification is by the American Board of Pathology or the American Osteopathic Board of Pathology. The organization of subspecialties within pathology varies between nations, but usually includes anatomic pathology and clinical pathology.