Spontaneous Regression of Eyelid Histiocytoma in a Maltese Dog

A 1-year-old neutered male Maltese dog was presented with a mass on the upper eyelid of the left eye (OS). A pinkish and alopecic mass was located in the nasal portion of the upper eyelid of OS. The mass was firmly attached to the eyelid and round-shaped with a diameter of 11 mm. Any spread to conjunctiva was not identified. On a cytological examination, cutaneous histiocytoma was confirmed, with the presence of small lymphocytes indicating later regression stage. The patient received no treatment and complete regression of the mass was verified 2 months later. The cytological examination was helpful for the diagnosis and staging of cutaneous histiocytoma. Canine eyelid histiocytoma can regress spontaneously, and thus medical or surgical treatment for removal should be considered carefully.