ETD

• Hydronephrosis CAKUT Renal pelvic dilatation

Background: Antenatal renal pelvic dilatation represents the most common abnormality detected during obstetric ultrasound screening. While moderate and severe forms (anteroposterior diameter [APD] ≥10 mm and ≥15 mm, respectively) are clearly associated with postnatal pathology, the clinical significance of mild, low-risk dilatations classified as UTD1 according to the 2014 UTD classification remains controversial. These conditions have traditionally been considered predominantly benign, with a high likelihood of spontaneous resolution and limited need for postnatal follow-up. However, emerging evidence suggests that a non-negligible proportion of these cases may progress to clinically relevant nephro-urological disorders.
Objective: To evaluate postnatal outcomes of mild antenatal renal pelvic dilatation through an observational clinical study and a systematic review of the literature, aiming to reassess the appropriateness of current follow-up protocols in patients considered at low risk.
Methods: A monocentric retrospective study was conducted on 270 patients (410 renal units) with antenatal renal pelvic dilatation (APD ≥4 mm). Prenatal ultrasound diagnosis was performed during the second trimester in 65.4% of cases and during the third trimester in 34.6%. All patients underwent serial postnatal ultrasound follow-up up to 6 months of age. Renal units were classified according to the UTD classification (2014), and outcomes were categorized as regression/stability, non-surgical worsening, surgical requirement, or complete resolution. Clinical and prenatal variables (sex, side, family history, APD) were collected and analyzed. In parallel, a systematic review of the literature was performed to compare the incidence of postnatal pathology and surgical intervention in patients with antenatal APD between 4 and 9.9 mm.
Results: Postnatal pathology was identified in 269 renal units (65.6%), of which 112 units (27.3%) required surgical or endoscopic treatment. The main diagnoses were ureteropelvic junction obstruction (UPJO, 53.2%), vesicoureteral reflux (VUR, 23.4%), ureterovesical junction obstruction/primary megaureter (UVJO, 14.9%), and urethral anomalies (8.2%), the latter being invariably surgical.
Among mild dilatations classified as low-risk UTD1, 18.1% required surgical intervention, compared with 36.8% in the UTD2–3 group, representing moderate and severe dilatations. Within the UTD1 group, the UTD1_B subgroup (third-trimester APD 4–7 mm) showed a surgical rate of 13.8%, whereas the UTD1_C subgroup (third-trimester APD 7–10 mm) showed a rate of 23.1%. The surgical risk of subgroup C was significantly closer to that of the high-risk UTD2–3 group (OR 1.97 vs C; p < 0.05) than to subgroup B (OR 3.39 vs B; p < 0.001).
Conclusions: Our findings, supported by data from the literature, confirm that mild antenatal renal pelvic dilatations are not invariably benign and that a substantial proportion may evolve into clinically relevant pathology. The observed heterogeneity supports the need for structured postnatal follow-up even in patients with APD <10 mm, particularly in those approaching the upper threshold. This study strengthens emerging evidence that low-risk dilatations require a reassessment of current risk stratification criteria and the adoption of more accurate predictive models.