Analysis of the tethered-bowel sign on abdominal CT as a predictor of malignant ascites.

The value of the "tethered-bowel sign" as a predictor of the nature of intraabdominal fluid was assessed. In the presence of moderate amounts of abdominal fluid, the sign was said to be positive if small or large bowel loops were not seen to float freely on computed tomographic (CT) images, and did not make contact with the anterior abdominal wall. A positive sign was significantly associated with the presence of malignant cells in the fluid (P less than 0.005). When equivocal cases were excluded, the sign had a sensitivity of 85%, a specificity of 93%, and an accuracy of 88%. In the study population (64% prevalence of malignant fluid), the sign had a positive predictive value of 96%, but a negative predictive value of only 78%. When equivocal cases were included, the sensitivity dropped to 69%, the specificity to 78%, and the accuracy to 72%. It is concluded that CT evidence of tethered-bowel loops strongly suggests a malignant cause of ascitic fluid.