Veterinary Anatomic Pathology: From Tissue to Diagnosis
Core concepts
The anatomic pathology domain tests whether you can move systematically from a gross or histologic observation to a defensible morphologic diagnosis and, where appropriate, an etiologic one. Candidates must be fluent in tissue injury and adaptation (hypertrophy, hyperplasia, metaplasia, atrophy, necrosis vs. apoptosis), the four cardinal signs of inflammation and their cellular mediators, healing and repair (granulation tissue, fibrosis, organization), circulatory disturbances (congestion, hemorrhage, thrombosis, infarction, edema), neoplasia (benign vs. malignant criteria, invasion, metastasis routes), and pigments and mineral deposits. Species-specific normal histology matters: know that some tissues (e.g., avian and reptile tissues, or the ruminant forestomach) have architecture that novices misread as pathologic.
Traps in questions
- Necrosis vs. postmortem autolysis: antemortem lesions show an inflammatory or reparative response at the margin; autolysis does not. Look for the reaction. A question showing zonal hepatic necrosis with a rim of neutrophils is antemortem.
- Coagulative vs. liquefactive necrosis: coagulative preserves tissue architecture (ischemia, most solid organs); liquefactive destroys it (brain infarcts, abscesses).
- Morphologic vs. etiologic diagnosis: "lymphoplasmacytic enteritis" is morphologic; "parvoviral enteritis" is etiologic. Read what is actually being asked.
- Metaplasia is not neoplasia: squamous metaplasia in airways is reversible adaptation, not carcinoma in situ.
- Metastasis routes: carcinomas favor lymphatics; sarcomas favor hematogenous spread, but exceptions exist.
Worked example / rule of thumb
Given a liver with a well-demarcated pale wedge and a hyperemic rim, ask: is architecture preserved? Yes → coagulative necrosis consistent with infarction. Then ask: is there inflammation at the border? If yes, it is antemortem. Rule of thumb: describe first (distribution, color, consistency, border), then interpret (process), then attribute (cause).