Acute flank pain: comparison of unenhanced helical CT and ultrasonography in detecting causes other than ureterolithiasis.

Several conditions can clinically mimic renal colic. We assessed the accuracy of non-contrast-enhanced helical CT and of ultrasonography (US) in offering an alternative explanation for flank pain. In a 3-year period, 181 patients with acute flank pain underwent US and non-contrast-enhanced helical CT in a blinded sequence. Their efficacy in detecting both alternative causes of pain and additional findings unrelated to the pain was assessed in 160 cases with a confirmed diagnosis. An alternative cause was found in 23 cases (14%). US gave 4 false-negative results (1 acute appendicitis, 1 ovarian cyst torsion, 1 diverticulitis, and 1 papillary necrosis) and 2 false-positive results (1 acute pyelonephritis and 1 diverticulitis), with a 78% sensitivity and a 98% specificity for nonlithiasic causes. CT gave 5 false-negative results (1 complicated ovarian cyst, 1 pleuritis, 1 epididymitis, 1 acute pyelonephritis, and 1 papillary necrosis) and 1 false-positive (1 simple ovarian cyst described as a complicated lesion), resulting in a 74% sensitivity and a 99% specificity for diagnosing alternative causes. There were 130 additional US findings in 68 patients and 151 additional CT findings in 77 patients. A wide spectrum of findings can be identified in subjects imaged for flank pain. Non-contrast-enhanced helical CT and US have comparable accuracy in diagnosing causes other than stone disease.