Sensitivity of transabdominal ultrasonography in detection of intraperitoneal fluid in humans.

The sensitivity and specificity of ultrasonography in detection of free intraperitoneal fluid is over 90 %. The lowest detectable volume of free fluid in humans is unknown. The distribution of intraperitoneal fluid was studied in 86 patients by transabdominal US in group A (n = 21, 10 ml of fluid), in group B (n = 15, 50 ml of fluid) and group C (n = 50, splenic trauma). Ultrasound detected fluid in 15 of 21 patients in group A, and in all patients in groups B and C. In group A 10 ml of fluid was found in 71 % of cases behind the bladder, and in only 5-14 % of cases in the upper abdomen. In group B 50 ml of fluid was found in all patients in the lower pelvis, but in only 20 % in Morison's pouch and in 7 % around the spleen. In group C 200-4500 ml of fluid was detected by US in 72 % of patients in the perisplenic space, in 60 % in Morison's pouch and in 42 % in the retrovesical space. Small volumes of free intraperitoneal fluid (10-50 ml) can be detected with current US scanners, but only near the site of injury. These results support the role of US as a primary imaging modality in abdominal trauma.