Resolution of hydronephrosis after pyeloplasty in children

Background: There is still a lack of knowledge regarding the natural course of resolution of hydronephrosis after pyeloplasty, and no consensus exists on how resolution of hydronephrosis is defined or when resolution is expected to occur.

Objective: To determine when resolution of hydronephrosis occurs following pyeloplasty, by type of obstruction and by surgical approach.

Methods: This retrospective study included 125 children age <15 years treated with pyeloplasty and followed for two years with repeated ultrasound and MAG3 scan. Children with single kidneys, bilateral disease, and without hydronephrosis were excluded. Children with re-interventions were excluded in the evaluation of hydronephrosis but not in terms of success rate. Outcomes time to resolution of hydronephrosis (Anterior-Posterior diameter (APD) <10 mm or >50% reduction of APD) and 2-year success rate. Exposure was surgical approach and type of obstruction (intrinsic/extrinsic). Survival analysis was performed, adjusting for age, gender, year, laterality, preoperative renal function on MAG3, calyces dilatation and APD in the multivariable analysis.

Results: At 12 months and 24 months follow-up, 90% and 93% had reached resolution, respectively. All children with persistent dilatation had improved drainage and stable or improved function on MAG3. There was no difference in time to resolution of hydronephrosis between open versus robotic-assisted laparoscopic surgery (adjusted HR 0.90, [0.54-1.52], p = 0.70), nor between different types of obstruction (aHR 0.84 [0.53-1.34], p = 0.47). Eight children had re-intervention, all identified within 3 months after primary surgery, and four had a postoperative drop on MAG3, giving a total success rate of 91% (121/135).

Discussion: The vast majority of cases resolve and do so within 12 months from surgery. Since the improvement of hydronephrosis seems small between the first and second year after surgery, the value of follow-up beyond 12 months could be questioned. Based on the present study and previous literature we would recommend that children with persisting dilatation should continue their follow-up with ultrasound beyond 12 months. Children with complete resolution of their hydronephrosis at 12 months do not likely benefit from further follow-up. The same follow-up protocol should be applied, regardless of whether the obstruction is intrinsic or extrinsic in nature, or the surgery is performed with open or robotic-assisted approach. Overall, the definition of resolution of hydronephrosis varies in the literature and have impact on the results and may compromise comparisons.

Conclusion: Surgical approach or type of obstruction does not seem to affect time to resolution of hydronephrosis after pyeloplasty in children. Follow-up with ultrasound beyond 12 months does not seem to benefit children with complete resolution.