Hair follicle nevi and accessory tragi: variable quantity of adipose tissue in connective tissue framework.

Controversy exists about the histologic differences between hair follicle nevi and accessory tragi. We examined 10 congenital lesions histologically, possible diagnoses of which were hair follicle nevi or accessory tragi. Two specimens out of the 10 had tiny, mature hair follicles surrounded by thick fibrous root sheaths, a few fat cells, and no cartilage. The subcutaneous fat cells of their bases were segmented by a connective tissue framework. They had histologic features of hair follicle nevi. One specimen had cartilage and abundant fat cells with a connective tissue framework in the nodule, as well as a conglomeration of numerous well-differentiated hair follicles. It possessed both elements of a hair follicle nevus and an accessory tragus. Seven specimens had abundant subcutaneous fat and showed a prominent connective tissue framework. These were typical accessory tragi. The present study suggests that the number of fat cells in the nodule or papule differs between these two conditions. All the lesions studied revealed a connective tissue framework in the subcutaneous fat. Histologic features of both hair follicle nevi and accessory tragi can coexist in a single lesion. Hair follicle nevi may represent incomplete accessory tragi with scant fat cells.