Fine-needle Aspiration Cytology of Cutaneous Endometriosis: A Series of 17 Cases with Literature Review.

Cutaneous endometriosis, a rare entity, is a type of extra pelvic endometriosis observed in 0.5%-1% of women. The most common sites include the abdominal wall, umbilicus, vulva, and extremities. It mostly occurs following gynecological surgery. Cutaneous endometriosis can mimic suture granuloma, hematoma, abscess, sarcoma, desmoid tumor, and metastasis due to variable presentations. Endometriosis shows a classic triad of epithelial cells, stromal cells, and hemosiderin-laden macrophages. The presence of any of the two features is diagnostic. We present 17 cases of cutaneous endometriosis diagnosed on fine needle aspiration cytology (FNAC) over 12 years (January 2013-December 2024). Cytomorphological features were analyzed and correlated with clinico-radiological findings and histopathology, where available. Age ranged from 22 to 42 years (mean age 32 years). The abdominal wall was the commonest site with 15/17 (88%) cases and a history of prior surgery (cesarean section, laparotomy, and episiotomy) was present in 14/17 (82%) cases. The most common symptom was swelling and cyclic pain together, seen in 13/17 (77%) cases. Cytology revealed the presence of benign epithelial cells and macrophages/hemosiderophages in all 17 (100%) cases and endometrial stromal cells in 11/17 (65%) cases. Epithelial atypia was observed in 6/17 (35%) cases. Histopathology follow-up was available in 6/17 (35%) cases and all were concordant. FNAC is a useful modality in the early diagnosis of endometriosis and helps to rule out other lesions with high accuracy. Epithelial atypia is a potential pitfall and awareness of the clinical presentation is key to prevent overdiagnosis.