Clinicopathologic features of epidermal cysts of the sole: comparison with traditional epidermal cysts and trichilemmal cysts*

Abstract

It has been described that the etiology of epidermal cysts on acral skin is different from that on non-acral skin; however, no papers have been published regarding the detailed histological differences between acral and non-acral epidermal cysts. In this study, we compared the clinicopathologic findings of epidermal cysts of the sole with those of traditional epidermal cysts and trichilemmal cysts. The cases studied were 12 epidermal cysts of the sole, 35 traditional (non-acral) epidermal cysts, and 12 trichilemmal cysts. The age and sex of the patients and the site, size, and microscopic findings of the lesions were evaluated. The pattern of keratinization was specifically focused on the evaluation of microscopic findings. Microscopically, most of the epidermal cysts of the sole showed the presence of parakeratosis and focal lack of a granular layer at least at the upper portion of the cyst wall. The cyst content of the epidermal cysts of the sole was predominantly compact orthokeratotic material. These pathological findings could be explained by the pathogenesis of epidermal cysts of the sole, namely invagination of the surface epidermis. Our study indicates that most cases of the epidermal cyst of the sole are considered to be a true traumatic epidermal inclusion cyst.