Can ultrasound and computed tomography replace high-dose urography in patients with impaired renal function?

Ninety-one patients with unexplained impaired renal function were investigated by high-dose urography, ultrasound and computed tomography (CT) without contrast. The aim was to evaluate the role of ultrasound and CT in renal failure, in particular their ability to define renal length and to show collecting system dilatation. In the majority of patients, renal length could be measured accurately by ultrasound. Measurements were less that those at urography because of the absence of magnification. Renal measurement by CT was not a sufficiently accurate indicator of renal length to be of clinical use. Both ultrasound and CT were sensitive detectors of collecting system dilatation: neither technique missed any case diagnosed by urography. However, in the presence of staghorn calculi or multiple cysts, neither ultrasound nor CT could exclude collecting system dilatation. CT was the only technique which demonstrated retroperitoneal nodes or fibrosis causing obstruction. It is proposed that the first investigation when renal function is impaired should be ultrasound, with plain films and renal tomograms to show calculi. CT should be reserved for those patients in whom ultrasound is not diagnostic or in whom ultrasound shows collecting system dilatation but does not demonstrate the cause. Using this scheme, ultrasound, plain radiography and CT would have demonstrated collecting system dilatation and, where appropriate, shown the cause of obstruction in 84 per cent of patients in this series. Only 16 per cent of patients would have required either high-dose urography or retrograde ureterograms.