ACVP Veterinary Pathology key terms

Irreversible cell death in living tissue, marked by cell swelling, membrane rupture, and inflammation. Karyolysis, pyknosis, and karyorrhexis are nuclear changes used to identify it microscopically.

Programmed, energy-dependent cell death producing individual shrunken cells with condensed chromatin and intact membranes. It typically incites little inflammation and is recognized by apoptotic bodies rather than widespread tissue reaction.

A membrane-bound fragment containing condensed chromatin and organelles that forms when a dying cell breaks apart during apoptosis. It is rapidly phagocytosed by macrophages or neighboring cells without triggering inflammation.

A pattern of necrosis in which tissue architecture is preserved as a ghost outline for a time, typical of ischemic injury in solid organs. Cells appear eosinophilic with lost nuclei.

Necrosis in which dead tissue is digested into a liquid viscous mass, classically seen in the brain after ischemia and in abscesses. Neutrophil enzymes and lack of structural support drive the process.

A form of necrosis producing friable, cheese-like, structureless eosinophilic material, characteristically associated with granulomatous inflammation such as tuberculosis. It combines features of coagulative and liquefactive necrosis.

Fragmentation of a dying cell's nucleus into scattered basophilic chromatin granules. It is one of the nuclear changes used to recognize necrosis on histologic sections.

Irreversible condensation and shrinkage of nuclear chromatin into a dense dark mass in a dying cell. It is a nuclear hallmark of necrosis and may precede karyorrhexis.

Progressive fading and dissolution of nuclear chromatin caused by deoxyribonuclease activity in a dying cell. The nucleus becomes pale and eventually disappears, aiding identification of necrosis.

An increase in tissue mass due to an increased number of cells, which may be physiologic or pathologic. It requires cells capable of division and is distinct from hypertrophy, which enlarges existing cells.

An increase in organ or tissue size caused by enlargement of individual cells rather than increased cell number. It is common in tissues with limited replicative capacity such as cardiac or skeletal muscle.

A reduction in organ or tissue size due to shrinkage of cells or decreased cell number. Causes include disuse, denervation, poor nutrition, reduced blood supply, and endocrine deficiency.

Reversible replacement of one mature differentiated cell type by another that is better adapted to a stressor. Examples include squamous metaplasia in airways and osseous metaplasia in soft tissue.

Disordered growth in which cells show variation in size, shape, and nuclear features with disturbed tissue arrangement. It is often a precursor to neoplasia but is not itself invasive.

Loss of cellular differentiation and resemblance to the tissue of origin, a hallmark of malignancy. Features include pleomorphism, hyperchromasia, prominent nucleoli, and atypical mitoses.

An abnormal mass of tissue whose growth exceeds and is uncoordinated with normal tissue, persisting after removal of the inciting stimulus. Neoplasms may be benign or malignant.

Spread of neoplastic cells from a primary tumor to a distant site where secondary growths develop. Routes include lymphatic, hematogenous, and transcoelomic seeding.

A malignant neoplasm arising from epithelial cells. It is named by prefixing the tissue or pattern of origin, and it typically spreads first via lymphatics.

A malignant neoplasm derived from mesenchymal cells such as fibroblasts, muscle, bone, or endothelium. Sarcomas often spread hematogenously and tend to be fleshy and poorly demarcated.

A benign neoplasm of glandular epithelium that remains confined and does not invade or metastasize. It often retains a recognizable glandular architecture and may be functional or nonfunctional.

A focal collection of macrophages, often epithelioid and sometimes multinucleated, formed in response to persistent antigens. It is a hallmark of chronic granulomatous inflammation.

A localized collection of pus, typically neutrophils and necrotic debris, walled off by granulation tissue. It results from pyogenic bacterial infection and undergoes liquefactive necrosis.

A localized area of ischemic necrosis caused by occlusion of arterial supply or venous drainage. Its shape and appearance depend on the organ's vascular anatomy and collateral circulation.

Inadequate blood flow to a tissue, depriving it of oxygen and nutrients and impairing removal of wastes. Prolonged ischemia is a common cause of necrosis and infarction.

Active increased blood flow to a tissue due to arteriolar dilation, producing a red, warm appearance. It is an active process, in contrast to passive congestion from impaired venous outflow.

Passive accumulation of blood within vessels due to impaired venous drainage or reduced cardiac output. Chronic congestion can lead to edema, hemorrhage, and hemosiderin accumulation.

Abnormal accumulation of fluid in interstitial tissue spaces or body cavities. It results from increased hydrostatic pressure, decreased oncotic pressure, lymphatic obstruction, or increased vascular permeability.

Protein-rich fluid that leaks from vessels due to increased permeability during inflammation, often containing cells and fibrin. It is distinguished from a transudate, which is low in protein and cells.

Low-protein, low-cell fluid that accumulates due to altered hydrostatic or oncotic pressures rather than inflammation. It is typically clear and does not clot readily.

A granulocyte that is the predominant leukocyte in acute inflammation and is capable of phagocytosis and killing of microbes. In many veterinary species its nucleus is segmented and lobulated.

A phagocytic mononuclear cell derived from blood monocytes that participates in chronic inflammation, tissue repair, and antigen presentation. It may aggregate into epithelioid cells within granulomas.

A golden-brown iron-storage pigment formed from breakdown of hemoglobin within macrophages. Its presence in tissue indicates prior hemorrhage or chronic congestion.

Escape of blood from vessels into tissues or body cavities. It may result from trauma, vascular disease, or disorders of coagulation and is classified as petechial, ecchymotic, or suffusive.

A small pinpoint hemorrhage in skin or mucous membranes, typically 1 to 2 millimeters in diameter. Petechiae suggest thrombocytopenia, vascular injury, or coagulopathy.

A larger flat area of hemorrhage into skin or mucous membrane, commonly called a bruise. It is distinguished from petechiae by size and from hematoma by lack of a palpable mass.

A panel measuring red cell mass, leukocyte numbers and differential, and platelet count in blood. It is a core screening test in veterinary clinical pathology and guides further testing.

The percentage of blood volume occupied by red cells after centrifugation, also called hematocrit when calculated. It assesses anemia, polycythemia, and hydration status.

A measure of immature anucleate red cells that still contain ribosomal RNA, used to classify anemia as regenerative or nonregenerative. In cats, aggregate and punctate reticulocytes are distinguished.

A reduction in red blood cell mass, hemoglobin concentration, or packed cell volume below reference limits. It is classified as regenerative or nonregenerative and by red cell size and hemoglobin content.

Anemia accompanied by an appropriate increase in reticulocytes, indicating adequate bone marrow response. Common causes include blood loss and hemolysis.

The leukocyte portion of a complete blood count, reporting total white cell count and differential. It helps identify inflammation, stress, and neoplastic or immune-mediated disorders.

An increased number of neutrophils in circulating blood, often reflecting inflammation, infection, or stress. A left shift with immature forms suggests active demand.

The presence of increased immature neutrophilic forms, such as bands, in peripheral blood. It indicates accelerated marrow release, usually in response to inflammation or infection.

A decreased number of circulating platelets that predisposes to petechial hemorrhage and prolonged bleeding. Causes include decreased production, increased destruction, and sequestration or consumption.

The number of platelets per unit volume of blood, usually measured by automated analyzer and confirmed on a blood smear. It is essential for evaluating bleeding disorders.

Microscopic examination of a stained blood film to assess cell morphology, platelet adequacy, and differential counts. It complements automated analyzer results and detects abnormalities they may miss.

A group of tests measuring enzymes, metabolites, electrolytes, and proteins in serum to assess organ function. Results are interpreted alongside history, physical findings, and other laboratory data.

Analysis of urine including physical properties, chemical dipstick tests, and sediment examination. It provides information on renal function, urinary tract disease, and systemic metabolic disorders.

Microscopic evaluation of cells collected by aspiration, swab, or fluid sampling to characterize lesions. It is rapid and minimally invasive but often less definitive than histopathology.

A minimally invasive technique using a thin needle and syringe to collect cells or fluid for cytologic examination. It is widely used to evaluate masses, lymph nodes, and effusions.

Microscopic examination of fixed, sectioned, and stained tissue to diagnose disease. It preserves tissue architecture and is often the reference standard for lesion characterization.

Removal of tissue from a living patient for histologic or other laboratory examination. Techniques include incisional, excisional, punch, and needle core sampling.