Page 100 - Differential Diagnosis in Small Animal Cytology, The Skin and Subcutis

Epithelial Tumours
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8.3 Follicular Tumours
VetBooks.ir Trichoblastoma

Benign tumour that derives or shows differentiation to the primitive hair germ cells.

Clinical features
• Common tumour in dogs and fairly common in cats.
• Age in dogs: 4–10 years old.
• In dogs it generally presents as a solitary, firm and alopecic mass, polipoid or dome-
shaped. In cats, masses are usually solitary and dome-shaped.
• In dogs, it more frequently occurs on the head, neck and at the base of the ears. In cats,
it most frequently occurs on the head and cranial half of the trunk.
• Trichoblastoma carries a good prognosis; the malignant counterpart of trichoblasto-
ma has never been described in dogs and cats, but it is rarely reported in people.

Cytological features

• Cellularity is variable from low to high.
• Background: clear to lightly basophilic. Haemodilution is possible.
• Neoplastic cells are cuboidal and are arranged in variably sized cohesive and uniform clus-
ters. Palisade arrangement is common.
• Nuclei are small to medium sized, with clumped chromatin and inconspicuous nucleoli.
• The cytoplasm is scant and lightly to moderately basophilic. It can contain a variable amount
of melanin pigment.
• Anisokaryosis and anisocytosis are minimal.
• Cells can be associated with a small amount of extracellular pink amorphous material
(possible basement membrane).
• Low to numeorus slender spindle cells can be found, often individually scattered in the
background (stromal cells).

Variants
• Ribbon and medusoid variants:
• Both variants are common in dogs and rare in cats.
• Cells are arranged in branching, winding and radiating columns (ribbons), generally two
cells in width. The cell cords radiate from a central island in the medusoid type.
• Cells are uniform and cuboidal. Cytoplasm is more abundant in the ribbon type.
• Granular cell variant:
• Uncommon form in dogs and rare in cats.
• Cells are individualized, medium to large and round to polygonal.
• Nuclei are oval, eccentric, with smooth chromatin and an inconspicuous nucleolus.
• The cytoplasm is abundant, has distinct borders and contains light purple granules.
• Variable numbers of cuboidal epithelial cells may be present.