Distinction between obstructive and nonobstructive hydronephrosis: value of diuresis duplex Doppler sonography.

OBJECTIVE: The purpose of this study was to determine the diagnostic accuracy of diuresis duplex Doppler sonography in distinguishing between obstructive and nonobstructive hydronephrosis by calculating the resistive indexes before and after administration of furosemide.

SUBJECTS AND METHODS: We prospectively studied 48 kidneys in 26 patients with suspected chronic renal obstruction. All patients underwent diuretic renography and duplex Doppler sonography before and after administration of furosemide. According to the findings at diuretic renography, kidneys were classified as nonobstructed (n = 12), indeterminate (n =9), obstructed (n = 8), or normal (n = 19). The mean resistive index of each kidney and the difference between the mean resistive indexes of both kidneys were calculated before and after administration of 0.5 mg furosemide per kilogram of body weight. A receiver operating characteristic curve was generated to determine the discriminatory resistive index value for diagnosing obstruction.

RESULTS: Resistive indexes were not significantly different between kidneys with nonobstructive dilatation and normal kidneys before and after diuresis. Significant differences in resistive indexes before and after diuresis were seen between kidneys with obstructive dilatation and kidneys with nonobstructive dilatation, and between normal kidneys. Kidneys with obstructive dilatation showed a significant increase in resistive index after administration of furosemide. In the indeterminate kidneys, furosemide had a heterogeneous effect on the resistive indexes, indicating obstructive resistive indexes in five kidneys and nonobstructive resistive indexes in four kidneys. Receiver operating characteristic analysis revealed a diuresis resistive index of 0.75, which resulted in an accuracy rate of 95% in diagnosing renal obstruction.

CONCLUSION: Diuresis duplex Doppler sonography is accurate in the differentiation of obstructed from nonobstructed kidneys and may facilitate the distinction between obstructive and nonobstructive hydronephrosis, notably in kidneys classified as indeterminate according to diuretic renography.