Steatocystoma multiplex: anatomic reevaluation, electron microscopy, and autoradiography.

Histologic and electron-microscopic features of steatocystoma multiplex were investigated. Specimens from 25 patients (8 females, 17 males) were serially cut and three-dimensional drawings constructed. Steatocystoma multiplex is a nevoid sebaceous duct and sebaceous gland tumor, originating from sebaceous follicles, but is not a dermoid tumor. One pilary unit continuously produces vellus hairs, which are trapped in the cystic cavity or in the pilary canal (trichostasis). Steatocystoma multiplex is connected to the epidermis by a straight or meandering epithelial cord, the remnant of the follicular infundibulum. This infundibulum is a more or less solid strand, often containing sebocytes or sebaceous lobulelike structures. A lumen, partly present in a few areas of the cord, is filled with cellular debris of keratinocytes, corneocytes, sebocytes, or trapped hairs. Steatocystoma multiplex has electron-microscopical features similar to the sebaceous duct and sebaceous glands of sebaceous follicles. The 3H-thymidine labeling index of the cyst wall with or without sebaceous acini is lower than in sebaceous follicles. Steatocystoma multiplex suppurativum, characterized by spontaneous rupture of the cyst, inflammation and scarring, mimics acne conglobata with hidradenitis-suppurativa-like lesions as seen in the acne triade or tetrade.