Unmasking the Hidden Uterine Cavity: Laparoscopic Excision of ACUM in an Adolescent Girl

Introduction: Accessory Cavitated Uterine Malformation (ACUM) is a rare congenital Müllerian anomaly characterized by a non-communicating accessory uterine cavity lined with functional endometrial tissue. It is usually located near the uterine cornua and presents in young, nulliparous women with severe dysmenorrhea and chronic pelvic pain. Due to its rarity and overlapping features with other gynecological disorders, ACUM is often misdiagnosed, delaying appropriate management. Case Presentation: An 18-year-old nulliparous female presented with severe, cyclical lower abdominal pain and dysmenorrhea persisting for three years, unresponsive to conventional medical therapy. Pelvic ultrasonography and magnetic resonance imaging revealed a well-defined intramyometrial cystic lesion near the right uterine horn, not communicating with the endometrial cavity, suggestive of ACUM. Laparoscopic evaluation confirmed the diagnosis, and the lesion was excised completely. Postoperative recovery was uneventful, and the patient reported complete resolution of dysmenorrhea during follow-up. Discussion: ACUM results from a developmental anomaly involving the Müllerian ducts, leading to the formation of an accessory uterine cavity with functional endometrium. The condition mimics endometriosis, adenomyosis, or uterine fibroids on imaging. MRI serves as the diagnostic modality of choice due to its superior soft-tissue characterization. Surgical excision of the accessory cavity is curative and provides long-term symptom relief, preserving fertility. Conclusion: ACUM, though rare, should be considered in young women presenting with refractory dysmenorrhea or chronic pelvic pain. Early recognition and laparoscopic excision result in excellent symptom resolution and improved quality of life.