Report of two cases of Accessory Cavitated Uterine Mass (ACUM): Diagnostic challenge for MRI.

Cystic adenomyosis is an unusual form of adenomyosis, characterized by a well-circumscribed cavitated endometrial gland and stroma, ≥ 1 cm in diameter, located within the myometrium. Few cases have been reported in the gynecological literature, with confusing naming such as: juvenile cystic adenomyosis, cystic myometrial lesions, cystic adenomyoma or juvenile adenomyotic cysts. The current preferred terminology is accessory cavitated uterine mass /or malformation (ACUM). We report here the cases of two 17 and 18 -year-old nulliparous women, who complained of severe dysmenorrhea early after the onset of menarche, with none or partial efficiency of medical treatment. MRI findings, with a follow-up in one case and surgical treatment in both cases, are described with an emphasis on physiopathology. The typical MR appearance is a large well-circumscribed round mass within the external myometrium, composed by an inner cystic hemorrhagic layer surrounded by a thick fibrous crown. The first-line treatment is laparoscopic surgery with mass resection. This typical MRI pattern must be a part of the knowledge of the radiologists.