Posterior urethral valves in boys: causes and care

The urinary system is made up of two kidneys, two ureters, the bladder and the urethra. Urine formed in the kidneys travels down the ureters to the bladder and leaves through the urethra. In a boy, the urethra begins at the bladder and runs the length of the penis.

The "posterior" urethra is the first stretch, closest to the bladder. In PUV, extra flaps of tissue there narrow the passage. infoKID describes PUV as the most common type of bladder outlet obstruction in newborn babies. The valves form while the baby is growing in the womb, and they can occur alongside other differences in the urinary system, such as kidneys or ureters that have not developed properly.

When the outflow is partly blocked, the bladder muscle works harder and the bladder wall can thicken. Great Ormond Street explains that the raised pressure may push urine backwards from the bladder into the ureters and kidneys, causing them to swell and potentially leading to kidney damage.

The degree of blockage varies from boy to boy, and so does the effect. In some, the kidneys are badly affected before birth. In others the obstruction is mild and nothing is noticed for years. This variation is why doctors speak cautiously about the outlook until tests have been completed.

Because the kidneys help to control blood pressure, fluid balance and growth, any lasting loss of function is relevant throughout childhood and into adult life. The NHS describes chronic kidney disease as a long-term condition in which kidneys do not work as well as they should, with blockages in the flow of urine among the recognised causes.

Many cases are suspected during pregnancy. Great Ormond Street notes that a routine ultrasound scan may show a swollen bladder, ureters or kidneys. After birth, a baby with a swollen bladder and constant dribbling of urine may be diagnosed. If the blockage was not severe, the condition can go unnoticed until a child develops symptoms.

• An enlarged bladder that can be felt as a lump in the lower tummy.

• Urinary tract infections.

• Difficulty passing urine, or a weak stream.

• Passing urine unusually often.

• Bedwetting after toilet training had been successful.

• Poor weight gain in a baby.

Great Ormond Street lists a usual set of investigations, adapted to each child. An ultrasound of the abdomen shows the kidneys, ureters and bladder. A micturating cystourethrogram (MCUG) shows urine moving from the bladder through the urethra and reveals whether it flows backwards towards the kidneys, which is called reflux.

Cystoscopy uses a thin telescope to look inside the bladder and urethra. Blood tests show how well the kidneys are working and whether the body has enough fluid. Further kidney and bladder function tests may be needed to check other parts of the system.

Parents are sometimes asked to wait while the team gathers all the results, because the outlook can only be explained once kidney function and the scan appearances are known together.

The first step usually deals with the immediate problem. Great Ormond Street says a thin plastic tube (catheter) is placed in the bladder to drain urine, while any infection and fluid imbalance are treated with antibiotics and fluids given into a vein.

The next step is to remove the valve tissue that is obstructing the flow. This is normally done through a cystoscope inserted along the urethra rather than by a traditional open operation. infoKID states that PUV need to be removed by surgery.

Some boys need extra procedures later, for example if the bladder does not empty well or reflux persists. Decisions are made by a paediatric urology and nephrology team, who also monitor growth, blood pressure and kidney function over time.

Great Ormond Street says the outlook depends on how much damage has already occurred in the kidneys, and that children need follow-up appointments on a long-term basis to check that no lasting damage has been done to the urinary system. Great Ormond Street lists bedwetting after successful toilet training and repeated urinary infections among the symptoms linked to PUV, so both are worth reporting to the specialist team.

Because the damage already present at diagnosis differs so much between boys, no single outlook applies to all. A specialist can explain the likely pattern for an individual child once the scans and blood tests are reviewed, and what the long-term kidney picture might look like.

Families should be reassured that PUV is not thought to run in families, and that nothing about diet or activity in pregnancy is known to cause it.

A boy with known or suspected PUV who has a high temperature, seems unusually sleepy or irritable, is not feeding or drinking, vomits repeatedly or passes very little urine needs urgent assessment. Call NHS 111 or take him to A&E if a baby or child becomes drowsy, floppy or difficult to wake, and use 999 for collapse or breathing difficulty.

Older boys who develop a fever with back or tummy pain, burning when passing urine or new difficulty weeing should be seen the same day, because infection in an obstructed system can damage kidneys quickly.

In the NHS, PUV is generally managed in specialist children's hospitals or in regional paediatric urology and nephrology services, with antenatal findings passed on from the fetal medicine team. Families may meet midwives, neonatologists, paediatric surgeons, nephrologists, specialist nurses and play specialists.

Some families also choose to seek an additional private paediatric urology opinion. If so, it helps to ask for copies of antenatal scans, MCUG images and blood results so that the NHS team and any private specialist work from the same information. Services and waiting times vary between hospitals.