Cytologic Aspect of Keratoacanthoma with Granulomatous Inflammation in a Dog

A 5-year-old Pekinese dog was evaluated for a back mass present for 1 year, which was diagnosed through fine needle aspiration cytology as a potential epidermal cyst or hair follicle tumor with secondary granulomatous inflammation. Surgical removal and histological examination revealed a well-demarcated nodule in the deep dermis and subcutis, characterized by a central cyst lined with basaloid cells and squamous epithelium, along with multifocal aggregation of macrophages and multinucleated giant cells. The final diagnosis was keratoacanthoma with granulomatous inflammation, and the mass did not recur 5 months post-surgery.