Purpose: We aimed to compare the Society for Fetal Urology and anteroposterior pelvic diameter classification systems in predicting the time to resolution of isolated hydronephrosis.
Materials and methods: We retrospectively reviewed isolated hydronephrosis cases prenatally detected and postnatally diagnosed between 1994 and 2018. Other urinary tract anomalies and vesicoureteral reflux were excluded. Baseline grades for both systems were collected. Anteroposterior pelvic diameter was classified as grade 1 to 4 over a scale of 5 mm. Resolution was defined by an anteroposterior pelvic diameter of less than 5 mm with Society for Fetal Urology grade I hydronephrosis. Time to resolution was analyzed using Kaplan-Meier curves.
Results: The study population consisted of 831 patients (1,028 renal units). Median followup was 26 months (range 6 to 260), and 559 units (54.3%) reached resolution during a median followup of 9 months (1 to 133). Resolution rates at 48 months were 81.7%, 65.6%, 37.6% and 5.2% for Society for Fetal Urology grades I through IV disease and 80.0%, 41.2%, 13.1% and 2.5% for anteroposterior pelvic diameter grades 1 through 4, respectively. Discrepancies between these grades were present in 481 units (46.8%). Society for Fetal Urology grades II to IV categorized as anteroposterior pelvic diameter grade 1 showed a superior cumulative rate of resolution (84.7%) vs anteroposterior pelvic diameter grades 2 to 4 categorized as Society for Fetal Urology grade I (53.2%, log-rank test p <0.001).
Conclusions: Hydronephrosis cases with anteroposterior pelvic diameter grades 2 to 4 but categorized as Society for Fetal Urology grade I have an inferior cumulative rate of resolution than vice versa. Society for Fetal Urology grades have little influence on resolution when anteroposterior pelvic diameter is less than 10 mm. Therefore, anteroposterior pelvic diameter is more useful in predicting the time to resolution.
Keywords: hydronephrosis; pyelectasis; urinary tract.