New techniques of ultrasound and color Doppler in the prospective evaluation of acute renal obstruction. Do they replace the intravenous urogram?

BACKGROUND: The intravenous urogram has long been the primary imaging modality in assessing acute renal obstruction. Newer ultrasound (US) techniques including pulsed and color Doppler allow the physiology of the urinary system to be interrogated via the resistive indices and ureteral jets. We sought to determine whether these new techniques would improve the ability of ultrasound to assess the presence of renal obstruction and replace the intravenous urogram in assessing acute ureteral obstruction.

METHODS: 32 patients suspected of having acute renal obstruction were evaluated with US and a KUB. A prospective diagnosis of complete, partial, or no obstruction was made. An intravenous urogram (IVU) was then performed as the "gold standard" for comparison.

RESULTS: Complete obstruction was correctly identified by the absence of a ureteral jet with no false negative studies. Using our ultrasound KUB protocol, partial obstruction was correctly identified in 77% of patients. All nonobstructed patients were correctly diagnosed. The overall sensitivity of combined ultrasound and KUB analysis was 84%, specificity 85%, and accuracy 87.5%.

CONCLUSION: Contemporary ultrasound employing pulsed and color Doppler is tedious and requires expertise not always available. Results with the intravenous urogram are more sensitive than specific. Unless contrast material is contraindicated, acute obstruction is best evaluated with intravenous urography.