Omental herniation through the esophageal hiatus mimics mediastinal lipomatous tumor

A 61-year-old man with a mediastinal abnormal mass on computed tomography is presented. Sagittal sections of magnetic resonance imaging (MRI) clearly indicated the continuity of the fatty mass from the abdomen to the thorax. The diagnosis was an omental herniation through the esophageal hiatus during the operation. First, we returned the omentum into the abdominal cavity, and then repaired the hiatus. The patient had an uneventful postoperative recovery. A herniation of the omentum through the esophageal hiatus is rare; this case is the tenth found in both English and Japanese literatures. The coronal and sagittal planes of MRI were useful in distinguishing the herniation of omentum through the esophageal hiatus from lipomatous tumor. It is our intention of raising awareness about the disease.