Obstructive vs nonobstructive dilatation of the renal collecting system in children: distinction with duplex sonography.

OBJECTIVE

The resistive index in cortical or arcuate renal arteries of children was calculated to determine whether obstructive uropathy could be differentiated from nonobstructive dilatation.

SUBJECTS AND METHODS

Kidneys (n = 176) were prospectively evaluated by using duplex Doppler sonography in patients 3 days to 20 years old. Obstruction was confirmed by renography with furosemide and/or by surgery.

RESULTS

The normal resistive index was 0.57 +/- 0.06 and the normal difference in resistive indexes between kidneys was 0.03 +/- 0.02 (n = 15). Abnormal values indicative of ureteropelvic junction obstruction were defined as the normal mean +/- 2 SD (i.e., a resistive index of > or = 0.70 plus a difference in resistive indexes between kidneys of > or = 0.08). Patients with unilateral dilatation and obstruction at the ureteropelvic junction (n = 20) had a mean resistive index of 0.77 +/- 0.05 and a difference in resistive indexes between kidneys of 0.16 +/- 0.05 (p < .001 compared with patients with normal kidneys and p < .001 compared with patients with unilateral dilatation without obstruction). Patients with unilateral dilatation but without obstruction (n = 16) had a mean resistive index of 0.63 +/- 0.06 and a difference between kidneys of 0.06 +/- 0.04 (values within normal limits). The positive and negative predictive values of the obstruction criteria for unilateral collecting system dilatation were 95% and 100%, respectively. After successful surgical correction of ureteropelvic junction obstruction (n = 29), patients had a normal mean resistive index of 0.61 +/- 0.05 and a normal difference between kidneys of 0.03 +/- 0.03. Five patients examined both before and after surgery showed a statistically significant drop in the resistive index of the obstructed kidney (0.75 +/- 0.03 to 0.65 +/- 0.05, p < .05) after surgery and a small rise in the resistive index of the contralateral kidney (0.56 +/- 0.04 to 0.63 +/- 0.04, p < .02).

CONCLUSION

The resistive index appears to be an effective parameter for the evaluation and follow-up of unilateral obstructive or nonobstructive ureteropelvic junction dilatation in children.