Accessory Cavitated Uterine Mass (ACUM) is a rare benign Müllerian anomaly characterized by an accessory endometrial cavity surrounded by normal myometrium, typically located near the insertion of the round ligament. It predominantly affects young women with severe dysmenorrhea and chronic pelvic pain. Due to its rarity and nonspecific appearance on ultrasound and CT, it is frequently misdiagnosed as a leiomyoma or adenomyosis. MRI is the imaging modality of choice for accurate diagnosis.
A 24-year-old nulliparous woman presented with chronic cyclic pelvic pain and severe dysmenorrhea. Ultrasound and CT abdomen suggested a uterine fibroid. MRI pelvis was subsequently performed for further characterization.
Well-defined hypodense intramyometrial lesion in the right uterine cornual region
Imaging features are highly suggestive of Accessory Cavitated Uterine Mass (ACUM).
The importance of MRI in the diagnosis of ACUM is:
Recognition of these characteristic MRI findings helps avoid misdiagnosis, unnecessary interventions and prolonged patient morbidity
Accessory Cavitated Uterine Mass (ACUM) is a rare congenital Müllerian anomaly, an accessory endometrial cavity within the myometrium, most commonly located near the insertion of the round ligament.
Severe dysmenorrhea and chronic pelvic pain is caused by recurrent hemorrhage due to cyclic bleeding from the functional endometrial lining.
ACUM is often misdiagnosed as a degenerating leiomyoma or cystic adenomyosis due to its rarity and nonspecific imaging on ultrasound and CT.
MRI is the investigation of choice as it shows the typical hemorrhagic cavity within a well-defined myometrial lesion, confirms the normal native endometrial cavity without communication and accurately shows the characteristic location of the lesion, allowing a confident pre-operative diagnosis and appropriate surgical planning..
The characteristic combination of a hemorrhagic non-communicating intramyometrial cavity adjacent to the round ligament with an otherwise normal uterus is highly suggestive of ACUM and helps distinguish it from its imaging mimics.
Accessory Cavitated Uterine Mass is a rare but important cause of chronic pelvic pain in young women. This case highlights the limitations of ultrasound and CT, both of which suggested a fibroid, whereas MRI established the diagnosis by demonstrating a characteristic hemorrhagic cavitated lesion adjacent to the round ligament. Familiarity with this entity and its MRI appearance is essential for early diagnosis and appropriate surgical management.
Learning Points
Dr. Vijay Thiraviyam R, MBBS, MD Radiology Kauvery Hospital, Chennai.
Dr. Malavika S, DNB Resident Kauvery Hospital, Chennai.
