Solution: Posterior urethral valves are congenitally thickened mucous membranes located in the posterior urethra distal to the verumontanum. The incidence is approximately 1:5,000 in boys only. The presentation can be related to UTI's, obstructive symptoms, palpable masses (hydronephrotic kidneys), hematuria, and failure to thrive. The findings on prenatal US can be pathognomonic with the "keyhole bladder". However, this is difficult to appreciate postnatally, so a VCUG is the diagnostic test after birth. You will see vesicourteral reflux, fusiform distention and elongation of the posterior urethra, diminution of the urethral caliber distal to the obstruction and you may see the curvilinear filling defect of the "valves" themselves at the level of transition. You can also see thickening/trabeculation of the bladder wall. All of these findings are present in this case. Treatment is surgical and prognosis is good if caught early enough. However, it is the most common cause of end-stage renal disease among young boys.