Adenomyosis with extensive glandular proliferation simulating infiltrating malignancy on magnetic resonance imaging.

We report a case of multicystic adenomyosis, which is an exceedingly rare benign tumor. The patient complained of an irregular menstrual cycle and abnormal genital bleeding that gradually increased in amount and frequency. The patient finally became severely anemic, and a hysterectomy was therefore performed. T2-weighted magnetic resonance imaging (MRI) indicated hyperplasia of the endometrium, with a myometrial lesion, where a high signal intensity multicystic mass was observed. The preoperative diagnosis was complicated by confusing MRI results. Postoperative macroscopic examination revealed a villous endometrium and a myometrium thickened with multiple small cysts containing serous transparent fluid. The final diagnosis, based on the hysterectomy specimen, was adenomyosis coexisting with simple endometrial hyperplasia. The MRI and positron emission tomography images are presented.