Cartilaginous choristoma of the lip in a dog

A six-year-old castrated male Maltese dog presented to a private animal clinic with a mass on the dog's lower lip without any other clinical signs. The mass (3 × 2 × 2 cm) was whitish and grossly well circumscribed, and a histopathological examination revealed that the mass was composed of normal cartilage tissue surrounded by fibrous connective tissues. Based on the gross findings, histopathology and anatomical location of the mass, the first diagnosis of a cartilaginous choristoma in a dog was made.