Uterus-like mass: MRI appearance of a very rare entity.

We describe a 37-year-old patient who presented with right lower quadrant pain and intermenstrual bleeding. MRI demonstrated a 5 x 5 cm lobulated mass centered in the right uterine wall interpreted as suspicious for malignancy. A total hysterectomy was performed, and the gross and histologic features were consistent with the diagnosis of a uterus-like mass. Uterus-like mass is a benign entity that can be found in a variety of organs, and is characterized by endometrium surrounded by smooth muscle. It is an extremely rare lesion with only approximately 15 cases reported in the current literature. There is a lack of imaging literature on this entity, which is primarily described in the pathology literature. Its histogenesis is uncertain, but is theorized to be metaplastic change, congenital anomaly, and/or heterotopia. However, given the MRI appearance in this case, we feel that uterus-like mass could be prospectively diagnosed or listed in a differential diagnosis. Copyright 2007 Wiley-Liss, Inc.