Accessory Tragus: A Rare Congenital Anomaly in a Dog.

Accessory tragus is a congenital malformation of part of the external ear, commonly reported in humans. Clinically, it is a benign, cutaneous mass located anywhere between the tragus of the ear and the angle of the mouth, along the migratory path of the first branchial arch. An accessory tragus was diagnosed in an otherwise healthy six-month-old male castrated American pit bull terrier that had a haired, pedunculated cutaneous mass on the left maxillary region from birth. Histologically, the mass was a polypoid extension of histologically normal haired skin with a central core of subcutaneous adipose tissue and well-differentiated elastic cartilage. To the authors' knowledge, this is the first report of this lesion in a non-human species. Retrospective examination of records from 2008 to 2018 at the Washington Animal Disease Diagnostic Laboratory failed to identify any other case. As accessory tragus in humans is commonly linked with other congenital anomalies and syndromes, recognition of this lesion in animals may aid in early discovery of other congenital defects and inform adequate excision of the lesion to prevent chondrodermatitis.