Abstract
Accessory cavitated uterine malformation is a rare congenital anomaly of Müllerian duct development that typically affects younger women of reproductive age. The most common symptoms include chronic cyclic pelvic pain and severe dysmenorrhea, although diagnosis is frequently delayed owing to its rarity, multiple differential diagnoses, and low patient awareness. This report describes the case of a perimenopausal woman with accessory cavitated uterine malformation. The patient exhibited a palpable mass in the right lower abdomen without notable chronic pelvic pain or dysmenorrhea. It was initially misdiagnosed as an adnexal cyst in the right region based on ultrasound imaging, and laparoscopic exploration revealed a mass in the uterine corpus, leading to a revised diagnosis of accessory cavitated uterine malformation, which was confirmed through intraoperative findings and histopathological examination. The postoperative outcomes were favorable. This case underscores the diagnostic challenges of accessory cavitated uterine malformation, given the limited research on its pathogenesis and the absence of distinctive diagnostic markers. Imaging and histopathology are essential for an accurate diagnosis. Surgical intervention, especially laparoscopy, remains the preferred treatment, with excision typically resulting in a favorable postoperative prognosis.