Time to resolution of isolated antenatal hydronephrosis with anteroposterior diameter ≤ 20 mm.

Data regarding spontaneous resolution of mild hydronephrosis consist of different etiologies, and hence, it is heterogeneous. The aim of this study is to evaluate spontaneous resolution rates and the time to complete resolution of antenatally detected isolated hydronephrosis in patients with renal pelvis antero-posterior diameter (RPAPD) ≤ 20 mm. Retrospective chart review of patients who were admitted to our pediatric nephrology clinic for the evaluation of antenatal hydronephrosis between 2011 and 2017 was conducted. Patients that had hydronephrosis with RPAPD ≤ 20 mm, < SFU (Society for Fetal Urology) grade IV on initial postnatal evaluation, and ≥ 3 months of follow-up with at least two renal ultrasounds (US) were included. Complete resolution of hydronephrosis was regarded as SFU grade 0 with a RPAPD of < 7 mm. Patients with ureteric and lower urinary tract abnormalities were excluded. There were a total of 276 patients who met the inclusion criteria. Median follow-up was 16 months (range 3-96 months). Hydronephrosis completely resolved in 198 patients (71.7%). Surgery was not required in any of the patients; however, nine patients (3.3%) showed progression to higher grades of hydronephrosis or increase in AP diameter. Median time to complete resolution of hydronephrosis was 6 months (range 2-35 months) in our study. Those with AP diameter < 10 mm became normal in median of 5 months, while it took median 11 months for patients with AP diameter 10-20 mm to become normalized (p < 0.001).Conclusion: Isolated antenatal hydronephrosis with RPAPD ≤ 20 mm would spontaneously resolve in 71.7% of the cases. Resolution may be expected to happen in 3 years, while the majority will take place in the first year of life. What is Known: • Antenatal hydronephrosis comprises an important amount of clinical visits. • Spontaneous resolution rates differ for various etiologies. What is New: • Isolated antenatal hydronephrosis with RPAPD ≤ 20 mm completely resolves within 3 years in approximately 72% of the cases. • Resolution can be observed within the first year of life in most of the cases.