Glomus cell tumour on the head of a cat.

Case summary: A solitary, sessile, non-ulcerated, freely mobile cutaneous mass approximately 1 cm in diameter on the left temporal region of a 7-year-old neutered female cat was examined. A fine-needle aspirate and wedge biopsy were performed by the referring veterinary surgeon and indicated a neoplasm of uncertain cell lineage. On histopathological examination, the deep dermis contained a discrete, non-encapsulated and vascular neoplasm with morphological and immunophenotypical features typical of a glomus cell tumour. Neoplastic cells were immunopositive for vimentin, muscle actin and smooth muscle actin, and immunonegative for cytokeratin, S100, desmin and von Willebrand factor (factor VIII-related antigen).

Relevance and novel information: Glomus cell tumours arise from modified smooth muscle cells and are rare in animals, particularly cats. Specific immunohistochemistry is of fundamental importance in the correct diagnosis of these tumours and should be considered for masses when cytology and histology results are inconclusive or uncertain.