Sweat gland hamartoma resembling human syringocystadenoma papilliferum in two young cats

Syringocystadenoma papilliferum, a hamartoma with mostly sweat gland, but also follicular infundibular elements, is described on the flank and head of two young cats. Clinically, lesions were cutaneous plaques characterized by irregular but sharply demarcated borders and a roughened, hyperpigmented surface. Complete surgical excision in one case was curative. Histologically, the lesion was limited to the superficial dermis and consisted of coalescing units of proliferating sweat glands. The proliferation was tubular or papillary, and may have been epitrichial, opening within dilated hypertrophied follicular infundibuli, or atrichial. Three types of epithelium were observed, recapitulating the formation of the follicular-sweat gland unit with infundibular, ductal and secretory epithelia. The glands reacted positively for alpha cytokeratin 8 and were supported by fibrous tissue with a plasmacytic, lymphocytic and neutrophilic infiltrate. As in humans, this lesion may be classified within the hamartoma-nevus-type category.