Apocrine hidrocystoma of the lower lip: a case report and literature review.

The hidrocystomas (HCs) are cystic forms of sweat gland resulting from proliferation of the apocrine secretory coil or eccrine duct. Apocrine -HCs are cystic lesions that arise from the apocrine secretory coil, while eccrine -HCs represent retention cysts of the eccrine duct. The commonest site for such lesions is around the eye, and they may also occur on the ears, scalp, chest, shoulders, or feet. However, HCs of the perioral region are uncommon. The differential diagnosis with minor salivary gland cyst or cystic neoplasms often poses a problem in this site. Here we report a rare case of apocrine -HC of the right lower lip for which excisional biopsy of the lesion was performed. Histopathologically, the lesion was a unilocular cyst lined by a double-layered epithelium of the apocrine secretory type. Immunohistochemically, the secretory epithelium was positive for mammaglobin, gross cystic disease fluid protein 15 (GCDFP-15), cytokeratin 7 (CK 7) and CK18, and the myoepithelium was positive for alpha-smooth muscle actin (α-SMA) and weakly positive for S100 protein. Here we present this very rare case of apocrine -HC of the lower lip, and discussed regarding differential diagnosis with minor salivary gland cystic lesion in the lip.