Posterior Urethral Valve
A rare, congenital, fetal lower urinary tract obstruction (LUTO) anomaly characterized by an abnormal congenital obstructing membrane or leaflets that are located within the posterior urethra associated with significant obstruction of the male bladder restricting normal bladder emptying.
Epidemiology
It is the most common anomaly of LUTO with a prevalence estimated at 1/4,750-6,250 male births. Posterior urethral valves (PUV) occur exclusively in males.
Clinical description
PUV represents a spectrum of severity ranging from a disease fatal in infancy to a disease that is minimal and may not manifest until later in life. In the most severe cases, characterized by antenatal oligohydramnios or anhydramnios, the newborn may presents with severe pulmonary distress and features of Potter sequence including wide-set eyes, flattened nose, receding chin and large, low-set ears deficient in cartilage. In toddlers and older children PUV may present with urinary incontinence, poor growth, urinary tract infections, hypertension, lethargy and ultimately renal failure.
Etiology
The embryology of the urethra is not completely understood, particularly as it pertains to pathologic anomalies. Several different theories have been proposed in the development of PUV. It represents a spectrum of severity based on the timing and severity of obstruction. Congenital obstruction of the urinary tract at a critical time in organogenesis has a profound and lifelong effect on kidney, ureteral and bladder function. The inability of urine to pass out of the body of the fetus results in oligohydramnios which in turn may lead to pulmonary hypoplasia and the features of Potter sequence.
Diagnostic methods
Postnatal diagnosis is suggested on renal ultrasound with findings of dilated, thick-walled bladder and a dilated posterior urethra. Postnatal diagnosis is confirmed with voiding cystotourethrography and cystoscopy.
Differential diagnosis
Differential diagnoses include anterior urethral valves, congenital urethral stricture, urethral atresia and Prune Belly syndrome. The diagnosis is then confirmed by postnatal physical examination and postnatal renal ultrasonography along with voiding cystourethrography.
Antenatal diagnosis
Antenatal diagnosis is based on ultrasound, possibly aided by magnetic resonance imaging studies. PUV is characterized by variably enlarged thick-walled, non-emptying urinary bladder and a dilated posterior urethra. Counseling is dependent upon the ultrasound findings that also suggest possible associated renal dysplasia at the time of prenatal diagnosis.
Genetic counseling
The majority of cases occur sporadically; however, some rare cases observed in siblings indicate autosomal recessive or x-linked recessive inheritance.
Management and treatment
Antenatal treatment involves urinary decompression with a vesico-amniotic shunt. Postnatally, PUV is treated using primary valve ablation or creation of a vesicostomy. Further surgical intervention is dependent on the status of the bladder function as well as renal function. Immediately after birth, infants are placed on antibiotic prophylaxis and a means of draining their bladder is accomplished using suprapubic or transurethral catheter diversion. Pulmonary function is assessed and fluid and electrolyte management performed.
Prognosis
The prognosis of PUV is variable depending on the degree of severity of the LUTO. Patients may be susceptible to urinary incontinence, urinary tract infections and progressive renal damage. Approximately one third of patients born with PUV progress to end stage renal disease and all patients need periodic long-term urologic follow-up care. Without intervention, patients are at risk of renal failure and bladder dysfunction. Fertility may be compromised in patients who are uremic.