Pathology
The medical discipline that studies the causes and mechanisms of disease through examination of tissues, cells, and body fluids. In veterinary practice, pathology encompasses histopathology (tissue examination), cytology (cell examination), and clinical pathology (blood and fluid analysis).
Pathology is the study of disease at the cellular and tissue level. A pathologist examines biological specimens — tissue biopsies, cell aspirates, blood, urine, body fluids — to identify disease processes, determine diagnoses, and guide treatment decisions. In veterinary medicine, pathology is divided into three main branches.
Clinical Pathology
Analysis of blood, urine, and other body fluids. Clinical pathologists interpret:
- Complete blood counts (CBC)
- Serum chemistry panels
- Urinalysis
- Coagulation profiles
- Endocrine assays
- Body fluid analysis (pleural fluid, peritoneal fluid, cerebrospinal fluid)
Clinical pathology drives the majority of routine diagnostic decisions in veterinary practice. Abnormal values on blood work or urinalysis often trigger further investigation, including imaging and tissue sampling.
Anatomic Pathology
Histopathology
Examination of tissue specimens under the microscope after fixation, processing, and staining. Biopsy specimens — incisional, excisional, or needle core — are submitted to a veterinary pathologist who evaluates:
- Tissue architecture and cellular morphology
- Presence and type of inflammation
- Evidence of neoplasia (tumor type, grade, margin assessment)
- Fibrosis, necrosis, or other degenerative changes
- Infectious organisms
Histopathology provides definitive diagnosis for most tumors and is essential for determining tumor type, grade, and completeness of surgical excision. The histopathology report directly influences treatment planning and prognosis.
Cytology
Examination of individual cells obtained through fine needle aspirate (FNA), impression smear, fluid aspiration, or scraping. Cytology is less invasive than biopsy and can be performed in-clinic, providing rapid preliminary information.
Cytology is useful for:
- Differentiating inflammatory from neoplastic processes
- Identifying tumor cell types (mast cells, lymphocytes, epithelial cells)
- Diagnosing infections (bacteria, fungi)
- Evaluating body cavity fluids
Limitations: cytology examines individual cells without tissue architecture, so it cannot assess tumor grade, invasion, or surgical margins as reliably as histopathology. It is a screening tool that often guides whether full biopsy is warranted.
Why Pathology Matters for Longevity
Accurate diagnosis is the foundation of effective treatment. Treating a mass as “probably benign” based on appearance alone risks missing a malignant tumor that requires aggressive intervention. Treating aggressively based on clinical suspicion alone risks unnecessary toxicity. Pathology provides the objective tissue-level data that connects clinical presentation to targeted treatment decisions.