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POSTERIOR URETHRAL VALVES
Pediatric Surgeon & Pediatric Urologist
B J Wadia Hospital For Children, Hurkisondas Hospital, Wockhardt Hospital, Mumbai
This is one of the major common urological anomalies found in boys. This may present with very non specific symptoms or may present with acute kidney failure. The cause of this anomaly is abnormal embryology and persistence of a fold. This remains and forms flaps or valves in the urethral passage of the male child. These valves are like one way doors that open inwards towards the bladder. When the boy attempts to pass urine, they come together, close or narrow the lumen of the urethra, this causes an obstruction to the passage of urine, and the boy strains to do so. The formation of these abnormal valves occurs around 4th month of gestation and depending on the severity of the obstruction, damage to the entire urinary system may be minimal or devastating and irreversible leading to renal failure with infection(sepsis) and death in newborns.
The effect of these valves occurs in a sequential back pressure effect on the urinary system. All this begins to occur even before the birth of the child as, the child normally passes urine in the amniotic fluid around it from before birth. The valves cause obstruction in the urethra. In the male urethra which is longer than the female urethra, there are 3 parts called the prostatic urethra that is surrounded by the prostate gland - also called posterior urethra; there is a small membranous urethra that passes thru the sphincter and then the pendular urethra within the penis. The valves are usually in the posterior urethra and hence are commonly called Posterior Urethral Valves(PUV). If the valves cause a severe obstruction, urine needs to be forced into the urethra distal to the valves, this gives rise to dilatation or ballooning of the urethra proximal to the valves. With passage of time, the bladder which is not being completely emptied, begins retaining urine and hence starts growing in size by stretching and expanding to accommodate the excess unpassed urine within. Each time the boy attempts to pass urine, the bladder contracts to empty totally, but is unable to do so due to the obstruction. This results in thickening of the musculature of the bladder - hypertrophy. With time, the continuously distended and hypertrophic bladder begins to transmit the pressure backwards, up the ureters and to the pelvis of the kidney. There is now a gradual build up of urine in the ureter that cannot empty into the bladder because - firstly, the bladder itself is at high pressure, and secondly, the thick bladder muscle acts like an obstruction where the ureter is joining the bladder and hence does not allow the urine to flow into the bladder. Meanwhile, the kidney continues to excrete urine as usual and there is more urine than can be accommodated in the ureter, which begins to balloon and dilate. This is then transmitted one step further to the pelvis of the kidney which also balloons and dilates till the elasticity allows. Once the capacity of the pelvis to stretch and dilate is reached, the pressure now falls on the kidney substance or parenchyma which is the main area that is responsible for making of urine. The pressure restricts the ability of the kidney to work normally and if there is no let up in pressure, the function of the kidney begins to deteriorate and if left uncorrected even after birth, or if the stagnant urine in the pelvis and ureter gets infected - that kidney starts failing. The same mechanism is also occurring on the other side kidney too. Thus, it is easy to understand why a severe uncorrected obstruction of the lower urinary tract can cause both the kidneys to loose function over a period of time; infection will only accelerate the process. This also illustrates that early diagnosis, early therapy may reverse this process and preserve the renal function.
Presentation of the boy will depend on the severity of obstruction. The boy may present at birth or as late as 3 - 4 years. The symptoms are the same - difficulty in passing urine, straining to pass urine, dribbling of urine, poor stream of urine. There may be distension of the lower abdomen caused by a stretched out filled up bladder. The common mistake that can be made is to diagnose this condition as phimosis as described elsewhere and then get a circumcision done. The symptoms may persist after this and then a suspicion of internal obstruction is thought of. Newborns may also be brought with few urinary symptoms and more non specific ones like abdominal distension, failure to thrive, signs of infection (sepsis) somewhere in the body, recurrent urinary infections with fever. Older children may also come with nonspecific complaints like not growing well, recurrent urinary infections, frequency of urine, burning during urination, pain in the flank etc. An examination may show an easily felt bladder that remains palpable even after the boy has passed urine. Observing the stream of urine while the child is micturiting will reveal a poor stream, falling close to the body, child straining while passing urine. When posterior urethral valves are suspected, investigations are a must to arrive at the diagnosis, the severity of the damage already caused, planning of the mode of treatment. Once again it cannot be emphasized enough that the reversibility of the damage to the function of the kidney cannot be judged at the time of diagnosis. Only, a regular follow up with the relevant investigations will tell the amount and presence of improvement even after the ideal and best therapy. This is the most frustrating part of this condition that often I have struggled hard, done multiple tests, procedures, surgeries to successfully relieve the obstruction, treated the infection aggressively only to see the child slide into renal failure at a later age and require renal transplant to save his life. This shows the importance of a long follow up of the child till he reaches adulthood.
Kidney Problems in Children Specialist Answer
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