Impact of bladder volume on renal pelvis dimensions in pediatric hydronephrosis

Objective: To evaluate the effect of pre-void and post-void bladder volume on the anteroposterior (AP) diameter of the renal pelvis in asymptomatic pediatric hydronephrosis and to determine its influence on ultrasonographic measurement variability. Method: A retrospective analysis was conducted on 113 children aged 4–9 years who were referred for renal ultrasonography (US) between 2019 and 2023. Patients were excluded if they had end-stage renal disease, congenital anomalies of the kidney and urinary tract, polycystic kidney disease, bilateral hydronephrosis, prior renal surgery, suboptimal image quality, or pathological findings on additional diagnostic tests such as scintigraphy or voiding cystourethrography. Standardized protocols were used to measure the AP diameter of the renal pelvis and bladder volume in both pre-void and post-void states, utilizing the ellipsoid formula. Paired t-tests and Pearson’s correlation coefficient were applied for statistical analysis. Results: The mean AP diameter of the renal pelvis significantly decreased from 7.43 ± 1.90 mm in the pre-void state to 5.62 ± 1.46 mm in the post-void state (p < 0.05). Similarly, bladder volume was markedly reduced from 183.6 ± 88.0 mL to 16.4 ± 14.9 mL (p < 0.05). Pearson’s correlation analysis revealed a strong positive correlation between pre-void bladder volume and the reduction in AP diameter (r = 0.65, p < 0.05), demonstrating the considerable effect of bladder volume on renal pelvic measurements. Conclusion: Incorporating pre- and post-void measurements into routine renal ultrasound protocols may enhance diagnostic accuracy, reduce variability, and improve clinical decision-making in pediatric hydronephrosis evaluation.