Right inguinal canal endometriosis mimicking a groin mass: a rare case report of round-ligament involvement.

Introduction and importance: Endometriosis is a chronic, estrogen-dependent disorder affecting over 10% of women, but extrapelvic involvement - particularly within the inguinal canal and round ligament - is rare and often mimics common groin pathologies, leading to diagnostic delays when cyclical symptoms are absent. Case presentation: A 31-year-old nulliparous woman presented with a gradually enlarging, painful right inguinal mass over 4 months. She had regular menses and no pelvic symptoms or prior abdominal or gynecologic surgery. Examination revealed a firm, non-tender mass without cough impulse. Pelvic MRI demonstrated an irregular nodular lesion within the right inguinal canal with T2 hypointensity, a small hemorrhagic focus, and progressive contrast enhancement, suggestive of endometriosis. Open surgical exploration identified a mass adherent to the round ligament and canal floor, which was completely excised, followed by mesh-reinforced repair. Histopathology confirmed ectopic endometrial glands and stroma consistent with round-ligament endometriosis. Postoperative recovery was uneventful. Clinical discussion: Inguinal endometriosis should be considered in reproductive-age women with unexplained groin masses, even without cyclical symptoms or known pelvic disease. MRI provides valuable diagnostic clues, particularly fibrotic T2-hypointense tissue with hemorrhagic elements. Complete excision is both diagnostic and therapeutic, and mesh reinforcement may reduce recurrence. Conclusion: This case highlights the importance of considering inguinal endometriosis in women presenting with groin masses. Early recognition supported by MRI and complete surgical excision ensures accurate diagnosis and excellent outcomes.