Posterior urethral valves (PUV)

What are posterior urethral valves?

In boys, a thin membrane that was not properly reabsorbed in the womb can remain in the part of the urethra close to the bladder. This membrane is called posterior urethral valves (PUV). It partially blocks the outflow of urine, the bladder has to work excessively hard to push urine out, its wall thickens, and the pressure is transmitted upward to the ureters and kidneys.

This is the most severe congenital blockage of the urinary tract in boys and occurs in about 1 in 5000–8000 boys.

How is it found?

During pregnancy

The typical picture on fetal ultrasound is: dilation of both kidneys and ureters, a large, thick-walled bladder, and a dilated urethra below the bladder (the “keyhole” sign). In severe cases the amniotic fluid decreases, which can affect lung development.

After birth

In children not diagnosed during pregnancy, these signs may appear:

• weak, dribbling urine stream, straining to pee,
• a full bladder that can be felt in the abdomen,
• febrile urinary tract infection,
• poor feeding, vomiting, not gaining weight,
• in older children, daytime wetting and a weak urine stream.

Diagnosis

• Ultrasound: dilation of the kidneys and ureters, thickness of the bladder wall.
• VCUG (voiding cystourethrogram): the main test that confirms the diagnosis. During peeing it shows a dilated posterior urethra and narrowing at the level of the valve. Reflux is often found as well.
• Blood tests: creatinine and electrolytes show kidney function.

Treatment

First step: making sure urine can drain

As soon as the condition is suspected, a thin catheter is placed in the bladder. This immediately reduces the pressure on the kidneys.

Cutting the valve (ablation)

Once the baby’s condition is stable, a very thin cystoscope is passed through the urethra under general anesthesia and the valve is cut. There is no incision. More details: cystoscopy and valve ablation.

In very small or premature babies, if the cystoscope cannot pass through the urethra, the bladder may be temporarily opened onto the skin of the abdomen (vesicostomy). The valve is cut after the child has grown.

Why is lifelong follow-up important?

Even after the valve is cut, kidneys and a bladder that were affected in the womb may not be completely normal. In some children, chronic kidney failure develops years later. Bladder function can also change over time (“valve bladder”): the bladder does not empty completely, pressure stays high, or a lot of urine is produced at night.

That is why follow-up is lifelong and includes:

• regular ultrasound, blood and urine tests,
• blood pressure measurement,
• assessment of bladder function (uroflowmetry, urodynamics),
• when needed, medication, emptying the bladder at night or catheterization,
• joint follow-up with a pediatric nephrologist.

Timely treatment and careful follow-up considerably extend the life of the kidneys.