Perianal Endometriosis: An Uncommon Site for a Common Problem

Endometriosis is the presence of uterine glands and stroma outside of the uterus. It is highly prevalent in women of reproductive age. It is usually found in the pelvis, with most cases being found on the peritoneum, ovaries, or deep in the pelvis. Extraperitoneal endometriosis is uncommon. Perianal endometriosis has an incidence of only 0.2%. We present the case of a 37-year-old woman with recurrent pain and swelling in the perineum at the site of a previous episiotomy scar. Initial imaging and assessment determined this to be scar tissue. Following re-presentation, it was mistakenly diagnosed as a perianal abscess, and the patient underwent incision and drainage. The wound failed to heal with significant induration. Further assessment of the wound was undertaken under general anesthesia. An excision of the affected area was performed, with histological analysis confirming endometriosis. This case highlights that extra-peritoneal endometriosis is a rare but treatable cause of recurrent, cyclical pelvic pain and swelling in the perineum. A high index of clinical suspicion is required due to its ability to mimic other pathologies, including abscesses and cysts. The primary management of perianal endometriosis is surgical excision. Where complete excision is not possible, medical management with hormone therapy should be considered.