Accessory cavitated uterine malformation (ACUM) is a possible cause of disabling dysmenorrhea. We present a case that is clinically atypical due to the late onset of symptoms (in the fourth decade of life, after pregnancy and cessation of suppressive hormone therapy), but at the same time, sonographically, fully corresponds to a typical ACUM, being one of the largest ever documented. Gynecologists and pelvic imagers should be familiar with the diagnostic criteria and consider ACUM as one of the differential diagnoses in women with pelvic pain and cystic myometrial lesion, especially when it is solitary.
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