BACKGROUND: Worsening hydronephrosis (HN) is a common marker of congenital ureteropelvic junction obstruction, yet no objective criteria exist for defining significant worsening HN. Our aim was to study the evolution of the antero-posterior renal pelvic diameter (APD) in a cohort of initially conservatively managed high-grade HN and report on the percentage worsening (PW-APD). METHODS: Patients (pts) presenting with isolated prenatal HN from 2008 to 2023 were retrospectively reviewed. Cases with Society for Fetal Urology (SFU) grade 3 and 4 HN in their first year of life who underwent at least two ultrasounds (US) were included. A subset initially under active surveillance underwent pyeloplasty due to worsening HN, was labelled "Pyeloplasty Group" (PG). Another subset with at least 2 years of conservative follow-up was labelled "Control Group" (CG). All US were reviewed by two investigators to record APD and SFU grade. APD was measured at the renal contour in the mid-renal transverse plane in supine position. For PG, we reviewed the last two US before surgery in addition to the initial one. For CG, we reviewed the last two US before 24 months of age or the last two US before resolution, in addition to the initial one. PW-APD was calculated by comparing APD at two time points; First- Last US and Previous-Last US. RESULTS: Sixty-five pts in PG and thirty-one pts in CG were included. Pts in PG deteriorated at a median age of 6.5 months. There was no difference in the initial APD between the two groups. In the First- Last US, SFU upgrading was noted in 45% of PG. Median PW-APD for all renal units in the PG was 69% and -31% for the CG. In PG, median PW-APD was 79% for SFU upgraded pts and 57% for those with stable SFU grades. In the Previous-Last US cohort, the median PW-APD was 50% for SFU upgraded pts and 39% for all renal units in the PG. A PW-APD of < 40% in the Previous-Last US was associated with no surgery, with an area under the receiver operating characteristic curve of 0.97, (p<0.001).
CONCLUSIONS: SFU upgraded cases demonstrated a PW-APD greater than 50% on average, whereas cases managed without surgery averaging less than 36%. This range of PW-APD could be an indicator of severity and could be used to tailor the frequency and intensity of follow-up. Further studies in other cohorts are needed to validate these findings.
