Poroid Hidradenoma: Case Report and Comprehensive Review of the Literature.

Poroid hidradenoma (PH) is a rare benign adnexal tumor of eccrine differentiation. It is the rarest of the four described variants of poroid neoplasms. PHs characteristically share a hybrid of the architectural features of the hidradenoma, namely, tumor cells are entirely intradermal with both solid and cystic components, and the cytologic characteristics of the poroid neoplasms, containing predominantly poroid and cuticular cells. Many published reports of PH since its original discovery in 1990 state that "very few" cases of PH can be found in the literature. Here, we have identified a total of 75 published accounts of PH, including the case presented here, as well as the associated patient demographics, lesion characteristics, treatment, and outcomes. We suggest that while uncommon, PH is likely not exceptionally rare and could be an underreported diagnosis.