Inverted Follicular Keratoses of the Buttocks

Abstract

Inverted follicular keratosis is a benign follicular tumor. Tumors classically demonstrate lobulated, endophytic growth with squamous eddy formation. The histologic differential diagnosis includes irritated seborrheic keratosis, trichilemmoma, verruca vulgaris, squamous cell carcinoma, and keratoacanthoma. The clinical differential diagnosis includes verruca, molluscum contagiosum, follicular cyst, and squamous cell carcinoma. In the past, a predilection for the head and neck of elderly men has been reported. Our experience is that the age, gender, and anatomic distribution of this lesion are more varied. Herein, we describe five cases of inverted follicular keratoses of the buttocks in middle-aged persons of both genders. These cases highlight the importance of considering inverted follicular keratosis as a possible buttock lesion because of its benign nature, in contrast to its clinical and histologic mimics. In addition, these cases are unique and relevant to the study of dermatopathology because they demonstrate a different age, gender, and anatomic distribution than previously reported.