Tumors of lower hair sheath:Common histogenesis of certain so-called “sebaceous cysts,” acanthomas and “sebaceous carcinomas”

Abstract

Under the terms “trichochlamydocyst” and “trichochlamydocarcinoma” is proposed a new unifying concept of the histogenesis of certain so-called sebaceous, keratinous and pilar cysts (cystic wens) and of proliferating epidermoid cysts and sebaceous carcinomas (solid wens). The majority of these lesions occur on the scalps of elderly women. Morphologically and histochemically their origin can be traced to the lower external root sheath of the terminal hair follicle rather than to sebaceous glands. In addition, a hitherto unrecognized lesion of the scalp, trichochlamydoacanthoma, is described for the first time and compared to its counterpart of other body regions, the keratoacanthoma. It, like keratoacanthoma, possesses a central keratin-filled crater but comprises instead lower external hair sheath epithelium as well as upper sheath or epidermal epithelium. Trichochlamydocarcinomas, the solid tumors of lower sheath origin, although usually non-aggressive, are occasionally capable of metastasis. It is not possible to predict by histologic or cytologic criteria their probable behavior so that a margin of normal tissue should accompany their excision.