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What is Posterior urethral valve and explain in detail?
Posterior urethral valve (PUV) disorder is an obstructive developmental anomaly in the urethra and genitourinary system of male newborns. A posterior urethral valve is an obstructing membrane in the posterior male urethra as a result of abnormal in utero development. It is the most common cause of bladder outlet obstruction in male newborns. The disorder varies in degree, with mild cases presenting late due to milder symptoms. More severe cases can have renal and respiratory failure from lung underdevelopment as result of low amniotic fluid volumes, requiring intensive care and close monitoring. It occurs in about one in 8,000 babies.

Presentation
PUV can be diagnosed before birth, or even at birth when the ultrasound shows that the male baby has a hydronephrosis. Some babies may also have oligohydramnios due to the urinary obstruction. The later presentation can be a urinary tract infection, diurnal enuresis, or voiding pain.

Complications
Incontinence
Urinary tract infection
Renal failure
Vesicoureteral reflux
Chronic kidney disease
Oligohydramnios

Diagnosis
Abdominal ultrasound is of some benefit, but not diagnostic.  Features that suggest posterior urethral valves are bilateral hydronephrosis, a thickened bladder wall with thickened smooth muscle trabeculations, and bladder diverticula.Voiding cystourethrogram (VCUG) is more specific for the diagnosis. Normal plicae circularis are variable in appearance and often not seen on normal VCUGs.  PUV on voiding cystourethrogram is characterized by an abrupt tapering of urethral caliber near the verumontanum, with the specific level depending on the developmental variant. Vesicoureteral reflux is also seen in over 50% of cases. Very often the posterior urethra maybe dilated thus making the abrupt narrowing more obvious. the bladder wall may show trabeculations or sacculations or even diverticuli.Diagnosis can also be made by cystoscopy, where a small camera is inserted into the urethra for direct visualization of the posteriorly positioned valve. A limitation of this technique is that posterior valve tissue is translucent and can be pushed against the wall of the urethra by inflowing irrigation fluid, making it difficult to visualize. Cystoscopy may also demonstrate the bladder changes.Centers in Europe and Japan have also had excellent results with cystosonography, although it has not been approved for use in the United States yet.

Classification
Posterior urethral obstruction was first classified by H. H. Young in 1919