Accessory cavitated uterine mass presenting as refractory dysmenorrhoea: a diagnostic challenge.

A woman in her 20s presented with severe progressive dysmenorrhoea that began within 1-2 years of menarche, was refractory to medical therapy and required repeated emergency department visits for parenteral analgesia. Ultrasonography suggested a uterine leiomyoma, whereas MRI demonstrated a unilateral haemorrhagic cavitated intramyometrial lesion without communication with the endometrial cavity, raising suspicion for a non-communicating Müllerian anomaly. Diagnostic laparoscopy revealed a small cavitated intramyometrial mass beneath the right round ligament with minimal pelvic endometriosis. Complete laparoscopic excision was performed while preserving the endometrial cavity. Histopathological examination confirmed an accessory cavitated uterine mass. The patient experienced complete resolution of dysmenorrhoea and remained asymptomatic at 6-month follow-up.