[Diagnostic imaging of calculi in the upper urinary tract--sonography vs. computerized tomography]

The choice of the most suitable technique for radiologic evaluation of upper urinary tract stones depends on the precise clinical questions that have to be answered. Many of these questions can still be answered by plain films of the abdomen and excretory urography. This review addresses the value of ultrasonography and computed tomography (CT) with respect to the two most important clinical questions, i.e. 1) presence/extent of obstruction/hydronephrosis and perinephric abscess in patients with acute flank pain; and 2) precise location, number and size of calculi. Because its sensitivity is comparable with CT and it is widely available, ultrasonography in the hands of experienced clinicians/radiologists may be preferred for evaluation of patients with acute flank pain. However, it must be emphasized that ultrasonography may totally miss acute ureteral obstruction/hydronephrosis within the first 12-24 hours. In children as well as in pregnant women, ultrasonography is still the technique of choice, but it may be replaced by magnetic resonance urography in the future. For precise stone location or detection of calcifications, however, the speed, safety and accuracy of unenhanced helical CT make this the most sensitive method and therefore the technique of choice. It also detects urinary calculi more accurately and exposes patients to less radiation than the traditional combined plain abdominal film/intravenous urography. Furthermore, CT can most readily reveal alternative diagnoses in patients with acute flank pain and other intraabdominal pathologies than stones.