med's go on Instagram: "The hallmark finding of posterior urethral valve (PUV) on a voiding cystourethrogram (VCUG) is the “keyhole sign,” which represents dilation of the bladder and the proximal (posterior) urethra due to obstruction at the level of the valves. When contrast fills the bladder and the posterior urethra, the obstructed and distended proximal urethra appears as a narrow “stem,” while the bladder forms the “head,” together resembling a keyhole. This radiologic appearance is highly