Extraperitoneal mass effect by ascites under tension.

Benign ascites may cause an extraperitoneal mass effect when it becomes loculated by adhesions or when peritoneal recesses are enlarged by ascites under tension. Five symptomatic patients were examined by computed tomography demonstrating ascites as the cause of an apparent mediastinal mass in 1, a retrogastric mass in 1, and a retroperitoneal mass displacing the right kidney anteriorly in 4.