Assessment of internal ureteral stent patency in patients with pyelocaliectasis: value of renal duplex sonography.

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Abstract
The purpose of this study was to evaluate duplex Doppler sonography in the assessment of internal ureteral stent patency. Thirty-three kidneys with pyelocaliectasis and an internal stent were studied with Doppler sonography and conventional sonography. Stent patency was proved by subsequent contrast-enhanced studies, direct inspection of the stent after removal, or clinical follow-up. The 11 kidneys with stent dysfunction had a significantly higher mean resistive index (0.78 +/- 0.08) than the 22 kidneys with patent stents (resistive index = 0.62 +/- 0.05) (p < .001). Eighty-two percent (9/11) of kidneys with occluded stents had elevated resistive indexes. The two occluded stents with normal resistive indexes were found in kidneys without significant obstruction before stent placement. Ninety-one percent (20/22) of patent stents were associated with a resistive index of less than 0.70. In the two cases of falsely elevated Doppler studies, the resistive index was obtained only 24-36 hr after placement of the stent; however, the resistive index was at least 10% less than that before stent placement. No significant correlation existed between degree of pyelocaliectasis shown on real-time sonography and stent status. In the presence of pyelocaliectasis after placement of an internal ureteral stent, intrarenal Doppler sonography can be used to accurately distinguish between patency and obstruction. Real-time sonographic findings (degree of pyelocaliectasis) are not useful in this clinical situation.

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