Types of Pathology

By Dr. Liji Thomas, MDReviewed by Danielle Ellis, B.Sc.

What is pathology?
Key branches of pathology
Modern applications and innovations in pathology
Why pathology matters
References
Further reading

What is pathology?

The word "pathology" literally means the study of disease processes. Pathology is a medical specialty that deals with the cause (or etiology) as well as the development and final effects of disease. It covers both the stepwise changes (pathogenesis) and final effects, both structural and functional, at gross and molecular level, that result from the abnormal condition.^1,2

The pathologic diagnosis is made from tissue samples of different kinds. Together with the physician's workup, it represents a reasonably informed determination of the disease affecting a given patient at that point in time.²

Multiple diseases have been diagnosed and treated without an understanding of the pathology. However, understanding the pathology provides the basis for further management as well as for mechanistic approaches to improve therapeutic strategies and develop screening tests.²

Key branches of pathology

 Anatomical pathology

This area of pathology involves the examination of biopsies (surgical specimens removed from the body) and autopsies (the examination of the whole body after death) to investigate and diagnose disease. This occurs at multiple levels, including:

• Gross anatomical structure of the sample
• Microscopic appearance of cells
• Chemical signatures in the sample
• Immunological markers on the cells
• Molecular biology of the cells, organs, tissues, and sometimes whole body

The subspecialties include:

Surgical pathology is a major branch of pathology involving the examination of tissue specimens obtained during surgery (e.g., breast lump excision or core biopsies, skin biopsies, and excision specimens following tumor removal). Both gross and microscopic analysis are performed.

Histopathology refers to the microscopic examination of thin sections of fixed or frozen tissues stained with appropriate dyes or antibodies to identify relevant cell structures.

Cytopathology refers to the cellular examination of free cells or tissue fragments from exfoliated samples or obtained by scraping or aspiration (e.g., cervical smear, bronchoalveolar lavage, and gastric aspirates).

Forensic pathology involves post-mortem examination or autopsy, where a corpse is examined to find the cause of death.

Dermatopathology is concerned with the study of skin specimens to identify the disease process and make a diagnosis.

Clinical pathology

This branch of pathology involves the laboratory analysis of body fluids (such as blood, urine, or cerebrospinal fluid) and bodily tissue for the diagnosis, treatment, and prevention of disease.³

The key subspecialities include:

• Chemical pathology, also called clinical chemistry, involves mainly the analysis of blood serum and plasma but also of various components in bodily fluids such as blood or urine.
• Immunology or immunopathology refers to the analysis of tissue and fluid samples relating to immune system disorders such as immunodeficiencies, organ-transplant rejection, and allergies.
• Hematology or hematopathology concerns the investigation and diagnosis of blood diseases.³

 Molecular pathology

Molecular pathology is a multi-disciplinary field that investigates the molecular basis of disease. It integrates genetics, molecular biology, and biochemistry. Beginning in 1764, when proteinuria was linked to renal disease, it accelerated with the advent of modern methods like RNA sequencing.

These include high throughput technologies such as new-generation sequencing (NGS), DNA microarrays, RNA sequencing, and nucleic acid amplification tests (NAAT). Most of these allow deep multiplexed sample analysis.⁷

Modern applications and innovations in pathology

Digital pathology and AI in diagnostics

Digital pathology is a relatively new area of pathology that uses advanced technology that allows slide information to be digitized and scanned with new imaging systems, including whole-slide image (WSI) scanners. This streamlines and speeds up the workflow while increasing readout precision and reproducibility.⁶

Artificial intelligence (AI) is an important advance in image acquisition and analysis. Such systems can see patterns missed by the human eye. They also store and share large amounts of data for remote applications, including teaching, research, review, diagnosis, and treatment.^{4, 5,6}

Molecular testing for personalized medicine

Personalized medicine is the ultimate goal of medical practitioners. Its aim is "to base medical decisions on individual patient characteristics (including biomarkers) rather than on [population] averages." It depends on identifying the molecular markers that underlie and explain the disease mechanism.

Molecular testing underpins the diagnosis of many conditions, cancer care, and treatment of infectious diseases. This is achieved by examining changes in biomolecules like nucleic acids and proteins in health and disease.^7.8

Role in public health and global disease management 

Pathology is pivotal to public health, as it dissects the causes and mechanisms of disease at all scales, from molecular to international. It enables disease surveillance systems to supply disease prevalence and incidence of specific diseases, investigates and manages outbreaks, and develops and manages screening programs for early detection and treatment.^7,8

Why pathology matters

Pathology is important in nearly every field of patient care as the bridge between science and medicine. By understanding how disease processes change cells and tissues, as well as the underlying molecular and genetic alterations, pathologists play a critical role not only in diagnosing disease but also in advancing medicine through research.

Their work underpins the discovery of early preclinical disease markers that can help screen for and diagnose diseases while they are still curable. It helps develop new diagnostics and therapeutics against a whole range of diseases. Pathology also pursues precision medicine, especially in oncology, helping to tailor therapies to the patient's specific genetic makeup and tumor characteristics.

References

1. Pathology. Available at https://www.britannica.com/science/pathology. Accessed on December 2, 2024.
2. Funkhouser, W. K. (2017). Pathology: The Clinical Description of Human Disease. Molecular Pathology. doi: https://doi.org/10.1016/B978-0-12-802761-5.00011-0. https://pmc.ncbi.nlm.nih.gov/articles/PMC7150310/.
3. Clinical Pathology Overview. Available at https://www.urmc.rochester.edu/encyclopedia/content.aspx. Accessed on December 2, 2024.
4. https://www.mcgill.ca/pathology/about/definition
5. https://www.nature.com/articles/s41379-021-00919-2
6. Baxi, V., Edwards, R., Montalto, M., et al. (2022). Digital pathology and artificial intelligence in translational medicine and clinical practice. Modern Pathology. doi: https://doi.org/10.1038/s41379-021-00919-2. https://www.nature.com/articles/s41379-021-00919-2.
7. Frohlich, H., Balling, R., Beerenwinkel, N., et al. (2024). From hype to reality: data science enabling personalized medicine. BMC Medicine. doi: From hype to reality: data science enabling personalized medicine. https://bmcmedicine.biomedcentral.com/articles/10.1186/s12916-018-1122-7.
8. Alugupalli, K. (2023). Role of Pathology in Public Health. Journal of Pathology and Disease Biology. doi: 10.35841/aapdb-7.4.156. https://www.alliedacademies.org/pathology-and-disease-biology/.

Further Reading

• All Pathology Content
• Pathology - What is Pathology?
• Advances in Digital Pathology
• Oral and Maxillofacial Pathologies
• Oral and Maxillofacial Surgical Procedures