猫における片側性副耳介軟骨腫：症例報告

An accessory tragus-a congenital malformation of part of the external ear-is an abnormal appendage developed from the first pharyngeal (or branchial) arch. In humans, an accessory tragus can be associated with other abnormalities as part of congenital malformative syndromes, most of which are transmitted in an autosomal dominant mode. Three cutaneous exophytic lesions were detected in the right preauricular region of a 2.5-y-old, castrated-male, European shorthair cat. Two of these lesions were submitted for histologic examination and were diagnosed as accessory tragi. They consisted of a vertical axis of loose collagenous tissue with hair follicles and sebaceous glands covered by a simple fold of epidermis. The epidermis was of normal thickness and slightly hyperpigmented. Only the pretragal lesion contained a central core of well-differentiated elastic cartilage. To our knowledge, accessory tragus has not been reported previously in cats and has been reported only once in veterinary medicine, in a dog with a solitary unilateral lesion. For pathologists, the diagnosis of this rare lesion may not be straightforward, especially if the cartilaginous core is absent or the location of the sample is unknown.