<unk>  is classified based on where along the urinary tract the obstruction occurs, including upper urinary tract obstruction and lower urinary tract obstruction. Depending on the location of the obstruction, one or both sides of the urinary tract will be involved. In approximately 50% of cases of congenital hydronephrosis, there is no known cause. In many cases, obstruction along the urinary tract in utero leads to some form of CAKUT mentioned above. Upper urinary tract obstruction Upper urinary tract obstruction includes the renal pelvis and upper ureters. Ureteropelvic junction obstruction Ureteropelvic junction obstruction (UPJ obstruction) is an obstruction at the level of the ureter and renal pelvis. It is the most common cause of hydronephrosis detected in utero and is the most common anomaly detected on prenatal ultrasounds. It occurs in approximately 1 in every 1500 live births, is most commonly seen in males, involves the left ureter twice as often as the right ureter. UPJ obstruction is transient in most cases. Lower urinary tract obstruction Lower urinary tract obstruction involves the lower ureters, urinary<unk>  and the urethra. Ureterovesicular junction obstruction Ureterovesicular junction obstruction (UVJ obstruction) is an obstruction at the level of the ureter and<unk> . It accounts for 20% of cases of hydronephrosis detected in utero. It is also most commonly seen in males and involved both sides of the urinary tract in approximately 25% of cases. Posterior urethral valves Posterior urethral valves (PUV) is an obstruction at the level of the urethra. It occurs in approximately 1 in every 5000 to 8000 live births and only occurs in males. Since PUV always affects both sides of the urinary tract, patients with posterior urethral valves are at the greatest risk for developing chronic kidney disease and end-stage renal disease due to obstructive uropathy. Ureterocele A ureterocele is a cystic dilation of the end of the ureter that can occur in the<unk>  and/or in the urethra. It occurs in approximately 1 in every 5000 live births, is most commonly seen in females and involves both ides of the urinary tract in approximately half of cases. Urethral stenosis Urethral stenosis is a narrowing of the urethra that prevents urine from exiting the<unk> .
Bladder outlet obstruction
Prostatic congestion
Urinary tract obstruction
Extravasation of urine
Urethral stricture
Bladder sphincter dyssynergia
Neurogenic bladder dysfunction
Underactive bladder