The most common etiology of sudden onset of flank pain in adults is acute urolithiasis. Identification of a stone in the ureter or resultant partial or complete ureteral obstruction confirms the suspected diagnosis. Intravenous pyelography (IVP) has been the classic diagnostic test of choice. Noncontrast helical computed tomography (CT), which was introduced in 1994, has the advantages of avoiding contrast exposure, identifying radiolucent calculi, evaluating nearby structures, and requiring a shorter time for examination. Worster and associates reviewed the literature comparing the accuracy of noncontrast helical CT and IVP in identifying acute urolithiasis.

Studies that compared these diagnostic tests from 1994 through 2000 were reviewed and included in the meta-analysis if they met prospective inclusion criteria, including requirements that both tests be conducted on the same day and that clinical follow-up occurred in at least 80 percent of the patients. The four studies (totaling 296 patients) that met all inclusion criteria showed noncontrast helical CT to be significantly more accurate in the diagnosis of acute urolithiasis. However, a systematic bias may have been present because noncontrast helical CT necessarily had to precede IVP to avoid residual contrast material. It is possible that some patients could have passed their stones after noncontrast helical CT and before IVP.

The authors conclude that noncontrast helical CT appears to be significantly better than IVP for identifying acute urolithiasis, although direct, randomized controlled studies would be useful to confirm this finding.

editor's note: Noncontrast helical CT provides significantly enhanced ability to view the full urinary tract and adjacent structures, including a detailed analysis of renal parenchyma. Intravenous urograms provide only gross images of the kidneys and miss other local pathology. When noncontrast helical CT is readily available, the amount of time required to evaluate patients in the emergency department is actually reduced, and potential contrast complications that may occur with conventional radiologic imaging are avoided. In a summary of the evidence of the best technique to diagnose a urinary tract stone, Chang comments that helical CT is clearly more accurate than IVP. Chang notes that the 56 percent negative predictive value of IVP makes a positive IVP finding very useful but a negative finding less useful. Clearly, when helical CT is available, it is the imaging study of choice for flank pain and presumed diagnoses of urinary tract stones.—R.S.