Comparison of Voiding Cystourethrogram with Cystoscopy in the Prediction of Presence of Posterior Urethral Valve

摘要

Posterior Urethral Valves (PUVs) are a major cause of short and long term morbidity in male children. They cause recurrent urinary tract infections and lead to chronic renal failure in a significant proportion of boys. The diagnosis of posterior urethral valves has historically been based off voiding cystourethrograms (VCUGs) and confirmed and treated by cystoscopy, which is the gold standard. To the best of our knowledge the literature is sparse on the role of definitive diagnosis of PUV based on VCUG and no data on the urethral ratios in the normal population.Aim: To determine the ratio of posterior to anterior urethral diameter as an objective means to predict presence of Posterior Urethral Valves (PUV) using cystoscopy as the gold standard and to determine normal urethral ratios in paediatric age groups.Materials and Methods: The study was conducted prospectively in 493 male children over 18 months. Urethral diameters were measured on VCUG and Posterior Urethra/Anterior Urethra (PU/AU) ratios derived. Cystoscopy was the reference standard. Diagnostic accuracy of ratios was calculated using Receiver Operating Characteristic (ROC) curves, best threshold values determined with corresponding estimates of sensitivity and specificity to decide optimal significant ratios. Age stratified normative ratios were calculated.Results: MCU has 97.96% sensitivity, 86.27% specificity, 87.27% positive predictive value (PPV) and 97.78% negative predictive value (NPV) value when compared with cystoscopy which is the current gold standard in the diagnosis of PUV. The Posterior Urethra/Anterior Urethra (PU/AU) ratio was found to be a valid indicator of the presence of PUV. The diagnostic ability of PU/average AU is the best of the three ratios (AUC 0.9055) in predicting the presence of a PUV on cystoscopy. PU/average AU value =2.11 suggests that the patient most likely has a PUV with an 83% sensitivity and 91% specificity, within 95% Confidence Interval of 0.8458-0.96527. With regard to calculation of the normal PU/AU ratio for each age group, we found a general trend of decreasing ratios with increasing patient age.Conclusion: VCUG is useful in predicting presence of PUV.Age group specific standard reference ratios can be used for identifying PUVs.