Cutaneous endometriosis as a diagnostic pitfall of fine needle aspiration biopsy. A report of three cases.

We describe the cytologic features of three cases of cutaneous endometriosis in young women (average age, 27 years); two cases presented as lower abdominal nodules associated with a previous cesarean section scar. The third case presented as a 5 x 4-cm inguinal mass. The smears were generally cellular, consisting of epithelial and stromal fragments. Epithelial cells showed large, hyperchromatic nuclei and moderate amounts of cytoplasm, with considerable nuclear overlapping. The stromal aggregates also showed crowded, overlapping nuclei and scant, admixed, hemosiderin-laden macrophages. These features, combined with isolated cells in the background, made differentiation from metastatic carcinoma extremely difficult. Cutaneous endometriosis can present a diagnostic pitfall on fine needle aspiration, especially in the absence of a previous history of abdominal surgery or established diagnosis of endometriosis.