Purpose: We sought to validate the role of serial ultrasound studies for detecting and excluding obstruction in high grade neonatal hydronephrosis.
Materials and methods: Between January 1996 and December 1998 all patients with prenatally diagnosed hydronephrosis underwent a protocol of antibiotic prophylaxis, ultrasound and voiding cystourethrography. All reflux-free patients underwent diuretic renography. Patients with high grade isolated unilateral hydronephrosis were included in the study. They were followed with 3 serial ultrasound examinations every 3 months in year 1 of life, biannually in year 2 and yearly thereafter. The trends in the changes in these studies were studied.
Results: Of the 153 patients 45 (29%) met study inclusion criteria. During a mean followup of 38 months (range 23 to 52) 16 patients (36%) who showed a trend of progressive hydronephrosis underwent pyeloplasty. The remaining 29 patients showed a trend of improvement in hydronephrosis. The drainage pattern on initial diuretic renography had only 63% sensitivity and 59% specificity for diagnosing obstruction. The same was true for the decrease in differential function of below 40% with 56% sensitivity and 66% specificity. Logistic regression analysis revealed that neither the initial grade of hydronephrosis on prenatal ultrasound nor the drainage-functional pattern on initial diuretic renography was a predictor of the subsequent need for pyeloplasty. All 16 patients who underwent pyeloplasty had improved or stabilized hydronephrosis after pyeloplasty.
Conclusions: A trend of progressive hydronephrosis on 2 consecutive serial renal ultrasound examinations serves as an early diagnostic sign of obstruction. Initial grade of hydronephrosis on initial ultrasound as well initial functional-drainage patterns on diuretic renography are not predictors of obstruction. Serial ultrasound is noninvasive and could replace serial invasive renal scans. Diuretic renal scans still have a role, especially as a baseline study to guide the frequency of serial ultrasound examinations.