Accessory Cavitated Uterine Malformation (ACUM): An Incidental Finding in Early Pregnancy.

Accessory cavitated uterine malformation (ACUM) is a relatively rare and underdiagnosed Müllerian anomaly. We report an ACUM identified incidentally at first-trimester screening in a woman in her early 30s with a spontaneously conceived pregnancy and a history of mild dysmenorrhoea. Transabdominal ultrasound demonstrated a well-circumscribed intramyometrial cavitated lesion beneath the left round ligament, initially anechoic and later with a small echogenic component, without communication with the endometrial cavity and with normal ovaries. The pregnancy progressed uneventfully and culminated in an uncomplicated term vaginal delivery. Postpartum imaging showed persistence of the lesion without change, and the patient remains asymptomatic under gynaecological surveillance. This case highlights the diagnostic challenge of ACUM in pregnancy and emphasises the need for uniform diagnostic criteria as well as prospective studies to define its natural history, reproductive impact, and optimal management.