DELAYED CONTRAST ENHANCEMENT OF ASCITIC FLUID ON CT - FREQUENCY AND SIGNIFICANCE

OBJECTIVE. Enhancing peritoneal fluid has been described as an uncommo n finding resulting from active extravasation of contrast material fro m the bowel, urinary tract, or blood vessels. We have noted that enhan cing peritoneal fluid occurs in other clinical settings. The CT number of ascites frequently increases between initial images obtained durin g 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 1 8 with benign disease) with free intraperitoneal fluid were examined w ith abdominal CT with IV contrast material. Active intraperitoneal ble eding or perforation of the bowel or bladder was not clinically suspec ted in any patient studied. When intraperitoneal fluid was detected on review of initial dynamic scans, a limited number of delayed scans we re obtained also. Significant enhancement was determined by comparing the CT numbers of fluid on dynamic and delayed images. RESULTS. Signif icant delayed enhancement of intraperitoneal fluid was seen in 54% of patients, with increases averaging 25 H (range, 7-54 H). Parametric an alysis indicated enhancement was inversely proportional to the amount of intraperitoneal fluid but independent of the type of IV contrast ma terial (ionic vs nonionic), time delay (range, 10-104 min), clinical h istory, and serum creatinine and serum albumin levels. Enhancement occ urred in both malignant and benign diseases and was more likely when s mall amounts of ascites were present. CONCLUSION. Enhancement of intra peritoneal 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. Caut ion should be used in interpreting the significance of high-attenuatio n intraperitoneal fluid on delayed images to avoid an erroneous diagno sis of active intraperitoneal bleeding or contrast extravasation.