Accessory cavitated uterine mass: a rare cause of severe dysmenorrhea.

We present a rare Müllerian anomaly known as "accessory cavitated uterine mass (ACUM)," which causes severe, refractory dysmenorrhea, and review the literature. A 17-year-old patient experienced severe, cyclic left-sided pelvic pain, correlating with menstruation. Magnetic resonance imaging (MRI) revealed a cystic lesion surrounded by myometrial tissue. Medical treatment with oral contraceptives was unsuccessful. Laparoscopic excision of the mass was performed, and histopathology confirmed the diagnosis of ACUM. At six months postoperatively, she remained asymptomatic, and follow-up MRI showed a normal-appearing uterus. ACUM is a rare Müllerian anomaly that is challenging to diagnose preoperatively, even with advanced imaging. Surgical excision remains the definitive treatment. This case highlights the importance of clinicians considering Müllerian anomalies in adolescents presenting with severe dysmenorrhea.