Posterior urethral morphology on initial voiding cystourethrogram correlates to early renal outcomes in infants with posterior urethral valves.

INTRODUCTION: Posterior urethral valves (PUV) is a leading cause of chronic renal failure in childhood. Bladder and posterior urethral deformity in infants with PUV are highly variable on initial voiding cystourethrogram (VCUG). Some types of deformity may be more important than others in determining the severity of the condition. Identification of specific VCUG features may allow for a simple, early screening assessment for patients.

OBJECTIVE: Determine whether morphologic features on the initial VCUG correlate to renal outcomes as measured by the creatinine nadir in the first year after ablation.

METHODS: Children with PUV treated by primary valve ablation before 12 months old and followed >1 year were identified. Initial diagnostic VCUG was evaluated for the bladder height to width ratio (HW-B), posterior urethral height to width ratio (HW-PU), and posterior-anterior urethral ratio (PA-UR). A trabeculation grade was assigned by three pediatric urologists, and reflux was noted. Univariable analyses with chi-square and t-test were used to compare bladder and posterior urethral morphology factors among those who obtained a creatinine nadir <0.8 or ≥0.8 mg/dL in the first year after ablation. Linear regression was performed to correlate morphology values with true creatinine nadir.

RESULTS: A total of 120 boys were ablated at mean age of 40.5 days (range 0-342) and followed for 5.9 years (± 3.85). Among these, 21 (17.5%) had a creatinine nadir ≥0.8 mg/dL. Mean overall HW-B and mean PA-UR were not significantly different between those with creatinine nadir <0.8 versus ≥0.8 mg/dL. Bladder trabeculation grade was not associated with creatinine nadir. For the entire cohort, only the difference in HW-PU was statistically significant between creatinine nadir groups with a much higher ratio among those with a nadir ≥0.8 (p < 0.001). Linear regression demonstrated a significant positive correlation between the HW-PU and creatinine nadir (R 2 = 0.097, p = 0.002). The presence of bilateral reflux is significantly associated with creatinine nadir ≥0.8 mg/dL (p = 0.001).

DISCUSSION: We investigate for the first time the association of morphology features on the initial VCUG with renal outcome in PUV patients. Posterior urethral deformity as quantified by a higher HW-PU ratio is significantly correlated with a higher creatinine nadir, whereas measured bladder morphology metrics are not. HW-PU may be an indirect measure of the severity of obstruction in posterior urethral valves.

CONCLUSION: The HW-PU appears to be a meaningful early morphologic metric for renal outcome.