Delayed contrast enhancement of ascitic fluid on CT: frequency and significance.

OBJECTIVE: Enhancing peritoneal fluid has been described as an uncommon finding resulting from active extravasation of contrast material from the bowel, urinary tract, or blood vessels. We have noted that enhancing peritoneal fluid occurs in other clinical settings. The CT number of ascites frequently increases between initial images obtained during bolus injection of IV contrast material and delayed images obtained after completion of the routine study. The objective of this study was to define the frequency and clinical significance of this phenomenon. SUBJECTS AND METHODS: Fifty patients (32 with malignant disease and 18 with benign disease) with free intraperitoneal fluid were examined with abdominal CT with IV contrast material. Active intraperitoneal bleeding or perforation of the bowel or bladder was not clinically suspected in any patient studied. When intraperitoneal fluid was detected on review of initial dynamic scans, a limited number of delayed scans were obtained also. Significant enhancement was determined by comparing the CT numbers of fluid on dynamic and delayed images. RESULTS: Significant delayed enhancement of intraperitoneal fluid was seen in 54% of patients, with increases averaging 25 H (range, 7-54 H). Parametric analysis indicated enhancement was inversely proportional to the amount of intraperitoneal fluid but independent of the type of IV contrast material (ionic vs nonionic), time delay (range, 10-104 min), clinical history, and serum creatinine and serum albumin levels. Enhancement occurred in both malignant and benign diseases and was more likely when small amounts of ascites were present. CONCLUSION: Enhancement of intraperitoneal fluid is a common and often striking finding on delayed CT scans after administration of IV contrast material. The phenomenon is nonspecific, occurring in a wide spectrum of clinical conditions. Caution should be used in interpreting the significance of high-attenuation intraperitoneal fluid on delayed images to avoid an erroneous diagnosis of active intraperitoneal bleeding or contrast extravasation.