Omental cyst: report of a case.

We report the case of an omental cyst, a rare type of abdominal cystic lesion that is difficult to diagnose preoperatively. A 43-year-old man with no clinical symptoms was admitted to our hospital for investigation of an abdominal cyst detected by ultrasonography (US). We performed diagnostic examinations including US, computed tomography, and magnetic resonance imaging. An omental cyst was diagnosed because of its position and connection to the surrounding tissues. Pathological examination of the surgical specimen revealed endothelial cells on its internal wall and colonies of lymphocytes, confirming a diagnosis of lymphangioma, which is the most common type of omental cyst.