[Fundamentals of cutaneous adnexal tumors]

Adnexal tumors of the skin are epithelial skin tumors with differentiation towards the adnexal epithelial structures of the skin, namely, hair follicle, sebaceous gland, apocrine gland, and eccrine gland. Adnexal tumors include hamartomas, benign and malignant neoplasms, and hyperplasias. The specific diagnosis of adnexal tumors is important because some lesions such as sebaceous neoplasms, cylindromas, or fibrofolliculomas are herald lesions of hereditary tumor syndromes (e.g., Muir-Torre syndrome, familial cylindromatosis, Birt-Hogg-Dubé syndrome). In this article, the classification of adnexal tumors of the skin is explained on the basis of embryology and histology and the main features of tumor-associated syndromes are summarized. Moreover, some conceptual controversies and problems in differential diagnosis of cutaneous adnexal tumors are discussed.