Eccrine hidrocystoma: two cases of Robinson and Smith types.

Two cases of eccrine hidrocystoma, one of which is a "classic" Robinson type and the other a Smith type, were reported. The walls of both cysts consisted mainly of two layers of flat or low cuboidal epithelial cells with eosinophilic cytoplasm. Immunostaining for S-100 protein was negative in the cells of the cyst wall of the Robinson type and only weakly positive in the inner luminal layer of the Smith type. Electron microscopically, the Smith type showed double-layered cuboidal lining and cell membrane interdigitations as junctions of neighboring cells without any characteristics of the secretory segment of sweat glands, indicating substantial similarity to those of the intradermal portion of the eccrine sweat duct.