Accessory Cavitated Uterine Malformation (ACUM): An Underdiagnosed, Treatable Cause of Dysmenorrhea

An uncommon and recently identified Müllerian anomaly is the accessory cavitated uterine mass (ACUM). It is distinguished by the presence of a noncommunicating auxiliary cavity inside the uterus, located near and surrounded by uterine smooth muscle, and bordered by functioning endometrium beneath the round ligament's insertion, with a perfectly healthy uterus, ovaries, tubes, and cavity. Given that it is a congenital ailment with a persistent Müllerian duct at the level of the round ligament, primarily resulting from gubernaculum dysfunction, it usually manifests clinically as childhood dysmenorrhea in girls. With a wide spectrum of differential diagnoses, including cystic adenomyoma, myoma, and adenomyosis, ACUM is an uncommon but treatable cause of severe dysmenorrhea and chronic pelvic pain in young girls. While MRI is quite accurate in diagnosing ACUM, it requires a high level of suspicion due to various differential diagnoses, even though ultrasonography can identify ACUM with ease. Similar entities have been misidentified or described in the past as adenomyoma (i.e., existence of histological organization similar to the uterus), cavitated uterus, and cystic adenomyoma (locally confined to myometrium), and myoma (resembles a lump inside the uterus). These are currently all believed to represent ACUM. In this case study and retrospective analysis, we emphasize the unique clinical presentation and care of an imaging discovery of ACUM in a 16-year-old girl.