Microcystic Adnexal Adenoma: The Benign Counterpart of Microcystic Adnexal Carcinoma.

Microcystic adnexal carcinoma (MAC) is a low-grade malignant neoplasm of slow growth and low metastatic potential, but locally aggressive. Architecturally, MAC is usually a poorly circumscribed neoplasm that tends to extend deeply into the dermis and subcutaneous tissue. We present here a lesion in which the histopathologic study showed a well-demarcated nodular lesion involving the mid dermis and composed of small cystic keratinous structures, solid aggregates of pale squamous cells without cytologic atypia and ductal structures. Although these neoplastic components resembled those of MAC, the sharp delimitation of the lesion as well as the absence of deep extension and perineural involvement supported the benign nature of this lesion. We have named this neoplasm microcystic adnexal adenoma, as the benign counterpart of MAC.