Background: Posterior urethral valve (PUV) is one of the serious causes of congenital bladder outlet obstruction in males. The pathological effects can present in varieties of occurrence and magnitude. Because of this variability, the urethral obstruction can cause diagnostic and management dilemmas. Diagnostic study of choice of posterior urethral valve is voiding cystourethrography (VCUG).

Objective: To demonstrate the posterior/anterior urethral caliber ratio that appears in voiding cystourethrography (VCUG) among the male pediatric patients with or without posterior urethral valve (PUV) for supporting diagnostic decision by imaging.

Material and Method: The study population consisted of male pediatric patients (≤15 years of age) who underwent VCUG from January 1^st 2007 to June 30^th 2014. Exclusion criteria were patients who had inadequate study, unavailable films, incomplete data in medical or radiological record, and/or were unable to undergo cystoscopy due to certain circumstances. Measuring of the posterior (P)/anterior (A) urethral caliber ratio was done. The urethral caliber ratio was calculated by dividing the maximal posterior urethral diameter by the maximal anterior urethral diameter. For each P/A ratio, sensitivity and specificity were plotted as a function of cutoff criterion, receiver operating characteristic (ROC) curves were constructed, and the areas under the curve (AUC) were calculated.

Results: A total of 432 patients were retrospectively reviewed. The median age was 2.6 years (range 1 day to 14 years). Median in ratio of 18 patients with positive VCUG and cystoscopy findings for PUV was 3.2 (1.72 to 7.41). A total of 413 patients with no symptom suggestion for PUV and negative VCUG findings for PUV demonstrate median in ratio 1.07 (0.48 to 5.56). The AUC that calculated by ROC curve was 0.991. At cut-off ratio 2.0, the sensitivity, specificity and accuracy were 94.7%, 96.9% and 96.8% respectively. At cut-off ratio 2.5, the sensitivity, specificity and accuracy were 73.7%, 99.3% and 98.2% respectively. At cut-off ratio 3.0, the sensitivity, specificity and accuracy were 57.9%, 99.8% and 97.9% respectively.

Conclusion: The calculation of posterior/anterior urethral caliber ratio provides us with objective measurement for benefit in diagnostic decision by VCUG. Best cut-off for optimum sensitivity and specificity is probably a P/A ratio of 2.0. Best cut-off for high specificity is probably 2.5 or 3.0.

Keywords: Posterior urethral valve, Urethral caliber ratio, Congenital bladder outlet obstruction