Unusual Complex Apocrine Tumor Consisting of Syringocystadenoma Papilliferum and Apocrine Hidrocystoma within a Single Lesion: A Case Report

Syringocystadenoma papilliferum (SCAP) and apocrine hidrocystoma (AH) are benign apocrine neoplasms that usually occur separately. SCAP arises predominantly in head and neck, while AH typically develop in periorbital area. We report a case of a 68-year-old male with an asymptomatic erythematous papulonodule that occurred on his back 3 years ago. Histologic examination showed cystic invagination extending from the epidermis into the dermis with some papillary projections. The invaginated portion was lined by epithelial bilayer composed of cuboidal and columnar cells, and decapitation secretion was observed in the inner epithelial layer. In the deep dermis, multiple cystic spaces with variable sizes were observed, and these cysts also presented double layers of the epithelium and decapitation secretion. According to such histologic features, the coexistence of SCAP and AH within a single lesion was demonstrated. The patient was recommended to completely remove the remaining lesion after punch biopsy, but he refused further surgical management. Herein, we report an unusual case of complex apocrine tumor with a rare composition in an atypical site.