Page 93 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

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8.2 Epidermal Tumours
VetBooks.ir Papilloma

Benign proliferation of the epidermis that can be viral or non-viral in origin.

Clinical features

• Non-viral papilloma (squamous papilloma):
• Age: no known age predisposition, though it is more frequently seen in old dogs.
• Lesions are small, generally 1–5 mm and generally exophytic.
• Most frequently localized on the face, eyelids, feet and conjunctiva.
• It might be triggered by trauma.
• Spontaneous regression is not expected.
• Viral papilloma (wart) (can be exophytic or inverted):
• Exophytic papilloma: uncommon in dogs and rare in cats; single or mul-
tiple; frequent on face, ears and extremities.
• Inverted papilloma: rare in dogs, usually younger than 3 years old; multiple and
usually on ventral abdomen.
• It can spontaneously regress within 6 weeks to 9 months.

Cytological features

• Cellularity is variable, often adequate.
• Background: variably haemodiluted.
• The aspirates are composed of large squamous epithelial cells that generally exfoliate individually.
• Cells are polygonal and angular with a low N:C ratio.
• Nuclei are round, central to paracentral. They are often large to very large and hyperchromatic.
The chromatin is clumped and nucleoli are not seen.
• The cytoplasm is abundant and pale basophilic. Viral papillomas can contain bright fuchsia
granulations and/or multiple small clear vacuoles. On histopathology, these cells are known
as koilocytes and are typical but not pathognomonic of viral papillomas.
• Small lymphocytes and reactive fibroblasts may be seen in the regression phase.

Differential diagnosis
Squamous cell carcinoma (well-differentiated form)