A 58-year-old man was admitted to the hospital because a huge abdominal tumor was found on ultrasonography (US) at a medical checkup. On physical examination, a movable, elastic soft mass with smooth surface was palpable on the left upper abdomen. The results of biochemical examination and the tumor markers, including CEA and CA 19-9, were nomal. Computed tomography (CT) and magnetic resonance imaging (MRI) disclosed a large cystic mass, measuring 9.0×13.0cm in size, which was located in posterior-lower portion of the stomach. Preoperative diagnosis was submucosal tumor of the stomach or a tumor arising from the greater omentum invading the gastric wall. A tatal extirpation of the tumor in combination with a partial resection of the involved gastric wall was performed. The extirpated tumor was 12.0×11.0×10.0cm in size, was entirely encapsulated, and composed of cystic and solid portions concomitantly.
Histologically, it was leiomyoma originating in the omentum.
Most of the tumors arising from the omentum have been proved malignant, such as leiomyosarcoma or leiomyoblastoma. Leiomyoma of the omentum is extremely rare, there have been only four cases including ours in the Japanese literature. Although, due to the absence of characteristic symptoms, it is difficult to make the preoperative diagnosis, US, CT and MRI are useful for the diagnosis.