Abstract
Epidermoid cysts are small, solitary, and slow-growing lesions that rarely appear in the perineum and mostly arise because of trauma. This study examined a huge perineal epidermoid cyst that slowly grew over eight years in a premenopausal woman. Ultrasonography showed that the hemorrhage in the cyst was a semisolid hypoechoic mass, which mimicked endometrioma, and was tentatively diagnosed as scar endometriosis in the perineum after vaginal delivery. This case study highlights the importance of wide surgical excision and histopathologic diagnosis, even with typical ultrasonography and surgical findings.