Cause: Congenital anomaly that leads to urinary outflow obstruction. Three types of valves have been described. Type I: a pair of leaflets that pass downward and laterally from lower border of verumontanum and extend around membranous urethra to fuse anteriorly at the 12:00 position. Type II: folds that arise from verumontanum and proceed proximally to divide into membranes; these are thought to be nonobstructive and probably are not true valves. Type III: centrally perforated diaphragms not related to verumontanum and may be cephalad or caudad to verumontanum (J Urol 1919;3:289).

Epidem: Most common cause of urinary outflow obstruction in pediatric population (J Pediatr Surg 1983;18:70). Incidence estimated at 1 in 5000-8000 male births. Accounts for about 10% of cases of prenatally diagnosed hydronephrosis (AJR 1987;148:1959).

Pathophys: Most plausible etiology of type I urethral valves is a failure of regression of ventrolateral folds of urogenital sinus during fetal development. Type I valves may be partially disrupted type II valves (Pediatr Surg Int 1992;8:45). Type III valves are probably the result of persistence of urogenital membrane during development. Congenital urethral obstruction occurs early in second trimester, after remainder of urinary tract has differentiated.
Maturation of urinary tract occurs in the setting of elevated bladder and urethral pressures, which may alter development of upper urinary tract. With severe obstruction, there may be oligohydramnios and pulmonary hypoplasia. Associated gu abnormalities include VUR in 50% of cases (J Urol 1982;128:994; BJU 1979;51:100) and UDT in 12% (J Urol 1980;124:101).

Sx: If oligohydramnios was present, the infant may develop respiratory distress.

Si: Prenatal US demonstrating bilateral hydronephrosis in the male infant, confirmed postnatal, delayed voiding > 24 hr after birth, palpable distended bladder, excessive thirst, polyuria, failure to thrive, dehydration. Older children may present with hematuria, incontinence, and recurrent UTI. Pneumothorax on chest Xray in newborn with respiratory problems.

Crs: Prenatal US has allowed for earlier detection of posterior urethral valves (J Urol 1992;148:125). In utero rx for posterior urethral valves and its consequences are still considered investigational and should be performed at select institutions. Children with posterior urethral valves diagnosed at birth are at higher risk for renal failure than those who have the condition diagnosed later in life. Good prognostic factors include serum creatinine (< 0.8 ng/dL after age 1 yr), VURD syndrome, urinary ascites, and a large bladder (J Urol 1990;144:1209; 1988;140:993). Of surviving infants with posterior urethral valves, 25-40% develop end-stage renal disease (J Urol 1994;151:275; BJU 1985;57:7). Of those who develop end-stage renal disease, 1/3 will do so soon after birth and the remainder in their teenage years (Smith GHH, Duckett JW. Urethral lesions in infants and children. In: Adult and Pediatric Urology. 3rd ed. St. Louis, MO: Mosby Yearbook; 1996:2411). Renal transplantation is an option for these children, but cmplc of renal transplantation higher in children < 2 yr (J Pediatr Surg 1992;27:629; J Urol 1988;140:1129).

Cmplc: Growth failure related to renal insufficiency and possible impaired sexual function and reduced fertility related to renal insufficiency and surgical rx

Diff Dx: Bilateral hydronephrosis on pre- and postnatal US carries diff dx of prune belly syndrome, urethral atresia, high-grade VUR, bilateral UPJO, and bilateral ureterovesical junction (UVJ) obstruction.

Lab: Serum electrolytes, BUN, creatinine levels. Immediately after birth, the infant’s serum creatinine level will reflect the mother’s creatinine and typically equilibrates in the next 96 hr (Urol Clin North Am 1990;17:343). UA, c + s, infants with respiratory distress need ABG.

Xray: Renal/bladder US is obtained to look for posterior urethral dilation, bladder size, wall thickness, ureteral dilation, and hydronephrosis and to assess renal parenchymal echogenicity and thickness and corticomedullary junction. Increased renal echogenicity on US suggests renal dysfunction (Radiology 1988;167:623). Lack of distinction of corticomedullary junction also suggests altered renal function (J Urol 1992;148:122). VCUG is gold standard for diagnosing posterior urethral valves. Typical findings include dilated posterior urethra with U-shaped cutoff at level of membranous urethra, often with incomplete bladder emptying (Gillenwater JY, Grayhack T, Howards SS, et al., eds. Adult and Pediatric Urology. 3rd ed. St. Louis, MO: Mosby Yearbook; 1996). Additional radiologic imaging such as renal scans may be indicated to assess renal function.

Rx: Initial rx involves stabilizing infant with correction of acidosis, underlying electrolyte abnormalities, infection, and respiratory issues if present. Immediate drainage via an 8- Fr feeding tube should be performed. Catheter placement may be difficult due to coiling of tube in dilated posterior urethra and bladder neck hypertrophy. Once infant is stabilized and serum creatinine followed, proceed with endoscopic valve ablation. Early valve
ablation within first months of life may result in recovery of nl bladder function and appearance (J Urol 1997;157:984).

If infant’s urethra is too small to pass an 8- Fr cystoscope, temporary cutaneous vesicostomy may be performed (J Urol 1990;144:1212; Urol Clin North Am 1974;1:484). Should see improvement in serum creatinine after primary valve ablation. If creatinine does not improve after valve ablation, vesicostomy or use of high diversion may be indicated. Use of high diversion is controversial (J Urol 1997;158:1008; Urol Clin North Am 1980;7:265).

Subsequent urodynamic evaluation is helpful in assessing bladder function in valve pts and in planning rx regimens (J Urol 1997;158:1011). Urodynamic abnormalities present in 20-88% of pts after valve ablation (J Urol 1990;144:122; 1979;121:769; Urol Clin North Am 1990;17:3737). Such findings include myogenic failure, DO, and decreased bladder compliance. Children with myogenic failure are initially rx with timed voiding and double or triple void regimens; those with DO and decreased compliance may benefit from anticholinergic therapy. Pts with significant myogenic failure may require CIC to empty their bladders. Pts with refractory poor compliance may require bladder augmentation.