Purpose or Case Report: Serial renal ultrasound (RUS) is often used as a surrogate for functional renal imaging among patients followed for hydronephrosis. However, it is unclear whether a lack of progression on serial RUS safeguards against loss of renal function. This study was performed to better characterize the association between findings on serial RUS and diuretic renography (DR) among children with unilateral high-grade hydronephrosis.
Methods & Materials: We retrospectively reviewed imaging among children <18 years with a history of unilateral Society of Fetal Urology (SFU) 3-4/Urinary Tract Dilation (UTD) P2-3 hydronephrosis. All patients underwent 2 RUS and 2 DR. Patients were excluded for comorbidities associated with bladder-level dysfunction, uninterpretable DR, or diuretic usage during only one RUS. Each RUS was paired with a contemporaneous DR and compared with a subsequent study pair. All studies were reviewed by an independent, blinded diagnostic radiologist. Change in hydronephrosis was determined by either (1) change in SFU/UTD grade or (2) any change noted by the radiologist. This was compared with change in DR, with a ≥5% change considered significant. Chi-squared and Spearman’s correlation analyses were performed.
Results: 85 patients aged 0-14 years (mean 12 months) were included in the final analysis. Patients were predominantly male (73%) with SFU 3/UTD P2 hydronephrosis (85%). Time between DR ranged from 1-112 months (mean 20). Worsening hydronephrosis was noted in 10/85 patients (12%) by SFU/UTD grade and in 28/85 patients (33%) by radiologist interpretation. Differential renal function decreased by ≥5% in 15/85 patients (18%). Changes in DR were significantly associated with changes in SFU/UTD grade on RUS among all patients (p=0.004, Table 1) and among patients with SFU 3/UTD P2 hydronephrosis (p=0.005, Table 2). Less substantial changes were not associated with DR findings (p=0.2). 10/70 (13%) patients with stable or improved SFU/UTD grade developed worsening renal function during the study period. When RUS and DR were directly compared, the Spearman’s correlation was poor (r=0.2, CI [0.03-0.4]).
Conclusions: While substantial changes in RUS findings were associated with corollary changes on DR, the overall correlation between imaging modalities was poor. 13% of children with SFU 3-4/UTD P2-3 hydronephrosis experienced a loss of renal function despite stable longitudinal RUS imaging. These findings are important to consider when counseling conservatively managed patients followed without DR.