The triangle sign: a CT sign of intraperitoneal fluid.

Ninety-four abdominal CT examinations of 91 patients with intraperitoneal fluid were reviewed, and in 25 scans (27%) triangular fluid collections were found within the leaves of the mesentery or adjacent to bowel. In a control group of 30 patients without CT evidence of intraperitoneal fluid, no triangular densities were identified. Triangular fluid collections were visualized in a higher percentage of patients when the quantity of intraperitoneal fluid was moderate to large, IV contrast was given, good bowel opacification was obtained, the amount of mesenteric fat was moderate to large, and the abdominal CT examination included cuts through the pelvis. A triangular fluid collection was reproduced in a cadaver by intraperitoneal infusion of saline. Percutaneous needle aspiration confirmed that the saline collection was responsible for the CT findings. The CT appearance of this new triangle sign is demonstrated.