Cytology of the penis and prepuce
Introduction
Disease or trauma of the penis and prepuce occurs in low numbers of dogs and is even less common in cats. These lesions typically cause swelling of the region and are rarely aspirated unless a mass-effect is present.
A few non-neoplastic diseases in the dog that may lead to swelling in the area include balantitis, paraphimosis, phimosis, priapism, foreign body reaction, and fracture of the os penis. In the cat, urethritis and damage secondary to urolith formation are more common (Foster, 2012c). Healthy cells of the penis are uniform, cuboidal to columnar epithelial cells (Kustritz, 2006).Neoplasia
Several tumor types have been associated with the penis and prepuce. Any of the tumors arising from the skin and subcutis can be found in this location. In dogs, the most common tumors of the penis are TVT and SCC. Virtually no information exists about tumors that occur on the penis of cats (Foster, 2012c; Lawrence & Saba, 2013c).
Transmissible venereal tumor
TVT is the most common tumor of the penis in dogs. The behavior and appearance are identical to those described for tumors of the vagina. As mentioned previously, cytologic samples are highly cellular and contain round cells with abundant lightly basophilic cytoplasm, distinct cytoplasmic vacuoles, and a round nucleus with finely stippled chromatin (Figures 11.52, 11.53).
Figures 11.52,11.53 Transmissible venereal tumor. FNA from a penile mass on a 7-year-old, neutered male Labrador Retriever. Cells are individualized and round with abundant, lightly basophilic cytoplasm and a large, round nucleus. The nuclei have stippled chromatin and a prominent, large, round nucleolus is often seen. Clear, distinct, round, cytoplasmic vacuoles are observed in most cells. Moderate anisocytosis and anisokaryosis are noted. Low numbers of erythrocytes and rare neutrophils are present in the background (Wright–Giemsa, 1,000? magnification).