Posterior Urethral Valves

What are posterior urethral valves?

At the distal end of the verumontanum, several folds, or plicae, arise and pass caudally to encircle a portion of the membranous urethra. These plicae occur normally and vary in the extent to which they encircle the urethra. When they fuse anteriorly, they form the most common type of posterior urethral valves (type 1).

Type 2 posterior urethral valves are mucosal folds that extend from the proximal end of the verumontanum toward the bladder neck; their very existence is controversial. Type 3 valves refer to a urethral diaphragm that occurs below the caudal end of the verumontanum.

How are posterior urethral valves detected?

Posterior urethral valves, which are the most common cause of bladder outlet obstruction in infant boys, cause changes in the bladder that are detected by US and cystography. These changes include enlargement, wall thickening, sacculation, and trabeculation of the bladder. Dilation of the posterior (prostatic) urethra above the valve can be seen on prenatal and postnatal US scans and with VCUG. Hydroureteronephrosis is often present, owing to either VUR or high pressures in the bladder. If rupture of a calyceal fornix occurs, urinary ascites or a urinoma or both can develop. Posterior urethral valves are confirmed cystoscopically and are treated with fulguration or incision.


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