Posterior urethral valves in male infants and newborns: detection with US of the urethra before and during voiding.

PURPOSE: To document the appearance and width of the posterior urethra with transperineal ultrasound (US) before and during voiding in male infants and newborns with posterior urethral valves. MATERIALS AND METHODS: Thirty-three patients with bilateral hydronephrosis underwent prospective transabdominal and transperineal US. RESULTS: Fifteen patients had proved posterior urethral valves (obstructed group); 18 patients had no obstruction (unobstructed group). In the obstructed group, the median posterior urethral width was 4.5 mm before and 10.0 mm during voiding. In the unobstructed group, the median posterior urethral width was 1.0 mm (P = .046) before and 4.0 mm (P < .001) during voiding. Bladder wall thickness was 3.0-7.6 mm (obstructed group) and 2.0-5.0 mm (unobstructed group; P < .001). With a posterior urethral diameter of at least 6 mm during voiding as a criterion for transperineal US diagnosis of obstruction, sensitivity was 100%; specificity, 89%; and positive predictive value, 88%. CONCLUSION: Transperineal voiding US is noninvasive and useful in diagnosing posterior urethral valves.