Histology and Pathogenesis
Eccrine hidrocystomas usually result from dilation of cystic excretory eccrine glands due to retention of sweat and dilation or blockage of the sweat duct. Under the microscope, eccrine hidrocystomas appear as unilocular cysts, which usually contain a single cystic cavity composed of 1 or 2 layers of cuboidal cells. They are located within the mid-dermal to superficial layers of the skin, especially around the eyes. Unlike their apocrine counterpart, there are no secretory cells seen and decapitation of cells is not viewed under the microscope. Histochemically, they stain positive for S100 protein (solitary type), whereas apocrine hidrocystomas do not. The cyst and epidermis do not communicate, and the periodic acid-Schiff (PAS)-positive granules are not observed.
Apocrine hidrocystomas appear as unilocular or multilocular under the microscope. The cyst wall is composed of an inner layer of secretory columnar epithelium. The epithelium is either a single or double layer of cuboidal-columnar epithelium, which lies above an outer myoepithelial cell layer. PAS- positive granules are observed in the presence of lipofuscin granules. Apocrine hidrocystomas also encompass papillary projections, which are not usually seen in the eccrine hidrocystomas. These projections are vascular connective tissue, covered by the secretory epithelium. Papillary projections then appear on the lumen of the cysts as an outgrowth extension from the wall of the cyst.
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Cite this: Hidrocystomas - A Brief Review - Medscape - Sep 05, 2006.