Cytology
The microscopic examination of individual cells collected from tissues, fluids, or masses to identify cell types, detect abnormalities, and guide diagnosis. Cytology is faster, less invasive, and less expensive than histopathology and is often the first diagnostic step for lumps, skin lesions, and body fluid analysis in dogs.
Cytology is the microscopic study of individual cells to evaluate their morphology, staining characteristics, and arrangement. In veterinary practice, cytology provides rapid diagnostic information from minimally invasive samples — often yielding results within minutes to hours, compared to the days required for histopathology (tissue biopsy processing).
Sample Collection Methods
Cytology samples can be obtained through several techniques:
- Fine-needle aspirate (FNA): A needle is inserted into a mass, lymph node, or organ, and cells are aspirated into a syringe. This is the most common cytology technique in veterinary practice.
- Impression smear: A glass slide is pressed directly against a lesion, ulcer, or cut surface to pick up superficial cells.
- Swab cytology: A cotton swab collects cells from ear canals, nasal passages, vaginal mucosa, or draining tracts.
- Fluid cytology: Body fluids (pleural effusion, abdominal fluid, joint fluid, urine sediment) are centrifuged and the cell pellet is smeared onto slides.
- Scraping: A blade edge scrapes cells from skin surfaces, useful for diagnosing fungal infections or superficial tumors.
What Cytology Can Identify
A skilled cytologist can often determine:
- Whether a mass is inflammatory, cystic, or neoplastic
- Whether a tumor is likely benign or malignant based on cellular atypia (nuclear size variation, mitotic figures, abnormal chromatin patterns)
- The cell type of origin: epithelial, mesenchymal, or round cell (lymphoma, mast cell tumor, histiocytoma)
- Infectious organisms: bacteria, yeast (Malassezia in ear infections), fungal elements, parasites
- Joint fluid abnormalities suggesting immune-mediated or septic arthritis
Limitations
Cytology examines individual cells without tissue architecture. This means it cannot assess:
- Tumor margins (whether a mass was completely removed)
- Degree of tissue invasion
- Tumor grading (which requires histopathological assessment of tissue organization)
- Some well-differentiated tumors that look similar to normal cells on cytology
For definitive diagnosis and grading, especially for mast cell tumors and soft tissue sarcomas, biopsy with histopathology is required.
Role in Longevity and Early Detection
Cytology is a frontline tool in cancer screening. Any new lump on a dog can be aspirated in a standard veterinary visit without sedation. Early cytologic identification of malignant cells enables faster treatment decisions, improving outcomes for conditions where time to intervention directly affects survival.