Pigmented hidrocystoma of the eccrine secretory coil in the vulva: clinicopathologic, immunohistochemical and ultrastructural studies.

A case of pigmented hidrocystoma of eccrine secretory coil is presented. A 47-year-old woman had developed a bluish black small nodule in the anterior portion of the labium minor a few years before entry. Microscopically, the cyst was lined by eosinophilic columnar epithelium with abundant brownish granules. There was a vague suggestion of decapitation secretion focally in the epithelial layer of cuboidal cells. This layer expressed distinct reactivity against CA19-9 with no reactivity for human milk fat globule-1 (HMFG-1). These features demonstrated that the cyst was not of apocrine nature but of eccrine derivation. In addition, positive immunoreaction for cytokeratin (CK)7, CK8 and CK19 defined the cyst as originating from the secretory coil of the sweat gland. Ultrastructurally, melanosomes in various stages were identified in most of the epithelial cells. These findings suggest that the present case was a hidrocystoma of eccrine secretory coil with abnormal melanin accumulation.