Congenital urethral obstruction: Cobb's collar or prolapsed congenital obstructive posterior urethral membrane (COPUM).

OBJECTIVE: To determine whether there are two distinct types of congenital obstruction of the proximal urethra.

PATIENTS AND METHODS: Three boys with a congenital bulbar urethral narrowing (Cobb's collar) were examined. Recent papers on congenital obstructive posterior urethral membrane (COPUM) were reviewed.

RESULTS: The more proximal lesion is a membranous obstruction which is able to prolapse as far as the bulbar urethra, but has paramedian folds that attach along the posterior wall of the urethra to the verumontanum, and is due to persistence of an embryological attachment between the distal verumontanum and the anterior wall of the posterior urethra. The more distal narrowing is not always obstructive and is primarily a bulbar urethral membrane, is independent of the verumontanum and external sphincter, and may represent a persistence of part of the urogenital membrane.

CONCLUSIONS: There are two distinct types of congenital obstruction of the proximal urethra, with the association to the verumontanum being the distinguishing feature.