Accuracy of sonography with a hydration test in differentiating between excretory renal obstruction and renal sinus cysts

Purpose: The aim of this prospective study was to determine whether sonography with a hydration test to induce diuresis can be used to reliably differentiate between excretory renal obstruction and renal sinus cysts.

Methods: We performed sonographic examination of all patients diagnosed with minimal or moderate obstruction of the intrarenal collecting system or renal sinus cysts on the basis of excretory urography, CT, or both between September 1, 1998, and October 31, 1999. The largest fluid-filled structures in the renal sinus were sonographically measured before and after each patient ingested 1.5 l of water. Cases in which the maximum diameters of the largest anechoic structures increased by at least 10% after hydration were diagnosed with excretory renal obstruction. The sonographic diagnoses were compared with the final diagnoses on excretory urography, CT, or both.

Results: Both kidneys were affected in 16 of the 36 patients examined, for a total of 52 kidneys. The sonographic diagnosis was consistent with the results of urography or CT in 48 (92%) of the 52 kidneys. The sonographic approach had a specificity of 92% and a sensitivity of 93% for the diagnosis of excretory renal obstruction, with only 1 false-negative and 3 false-positive results.

Conclusions: When used with the stimulated diuresis test, sonography can reliably distinguish between excretory renal obstruction and renal sinus cysts and can be used as an alternative to other imaging techniques such as urography.