Decidualized endometrioma diagnosed by fine needle aspiration cytology: a case report with immunocytochemical confirmation.

Endometriosis is defined as ectopic endometrial tissue which can respond to hormonal stimulation. Cutaneous endometriosis is a rare pathologic entity that can represent a clinical diagnostic challenge. We report a case of a decidualized endometrioma in a 24-year old pregnant African American woman diagnosed by fine needle aspiration cytology and confirmed by immunocytochemistry using CD10, ER, and Calretinin. The awareness of the pathologist of the cytologic characteristics of this uncommon entity is important to avoid diagnostic pitfalls and unnecessary diagnostic interventions during pregnancy.