Page 110 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

Epithelial Tumours

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Pilomatricoma
VetBooks.ir Benign tumour that arises from the germinative cells of the follicular

matrix or hair bulb.

Clinical features
• Uncommon benign tumour in dogs, accounting for approximately 3% of all skin
epithelial neoplasms. The malignant counterpart is rare. Very rare in cats.
• Age in dogs: 2–7 years old.
• Lesions are usually solitary, firm and well circumscribed. Occasionally, multiple
lesions can occur.
• Masses may have a gritty or bony consistency.
• It frequently occurs on legs, dorsal trunk, neck and tail.
• Most canine pilomatricomas are benign; malignant pilomatricoma is locally aggres-
sive, with invasion and/or metastasis to the bone and metastasis to lymph nodes and
lung.
• Over-represented canine breeds: Standard Poodle, Kerry Blue Terrier, Old English
Sheepdog, Soft-coated Wheaten Terrier, Airedale Terrier, Bouvier des Flandres,
Bichon Frise, Schnauzer and Basset Hound.

Cytological features
• Aspirates usually yield a large amount of specimen, with or without low numbers of intact nucle-
ated cells.
• Characterized by high numbers of ghost cells. These are anucleated squamous epithelial
cells with a pale central area. They are polygonal, often hexagonal, and relatively small com-
pared with the polygonal anucleated squamous epithelial cells from the infundibulum.
• Occasionally, small clusters of uniform cuboidal epithelial cells may be found.
• Secondary inflammation is possible, especially if the keratin is exposed to the surrounding
tissues.
• Malignant pilomatricoma may be well differentiated and may not differ morphologically
from a benign pilomatricoma. Occasionally, variable features of malignancy, such as slightly
disorganized clusters, increased anisokaryosis and anisocytosis and mitotic figures may be
observed. Areas of necrosis may be present.

Differential diagnosis
Follicular cyst (matrical cyst)