The nature of pigment in pigmented apocrine hidrocystoma.

Apocrine hidrocystomas are often pigmented clinically. The cause of this pigmentation is not known. A case of pigmented apocrine hidrocystoma is presented with evidence of melanin as the underlying mechanism of the pigmentation. Review of an additional 150 cases suggests that this is rare. The Tyndall effect, analogous to that seen in blue dome cysts of fibrocystic disease of the breast may be the likely explanation of the pigmentation seen clinically in most cases of apocrine hidrocystomas.