Anterior urethral valve (ORPHA:435372)
A rare, congenital, fetal lower urinary tract obstruction (LUTO) anomaly occurring in males and characterized by a posteriorly directed semilunar fold arising from the floor of the anterior urethra and causing urethral obstruction during micturition. The valves may be located anywhere distal to the membranous urethra. Clinical presentation is highly variable, depending on age and degree of urinary obstruction, and includes urinary incontinence, urinary retention, weak urinary stream, post-micturitional dribbling, bulging on the ventral penis, urinary tract infection, and urosepsis.
Epidemiology
The exact prevalence is unknown, although it occurs less frequently than posterior urethral valves. This disease affects males only.
Clinical description
Anterior urethral valve (AUV) can be located anywhere distal to the membranous urethra, occurring either in the bulbar urethra (40%), penoscrotal junction (30%), or in the penile urethra (30%), and are occasionally associated with urethral diverticulum. Clinical presentation is highly variable and may occur prenatally with hydronephrosis or a distended bladder, or between birth and adolescence with urinary tract infections or weak urinary stream. Other clinical manifestations include lower urinary tract obstruction, palpable distended bladder, urinary incontinence, renal insufficiency, renal dysplasia, a thickened, trabeculated bladder, and vesicoureteral reflux. After valve ablation, patients typically void spontaneously; however, over 20% of patients have abnormal renal function after treatment, which can range from stable azotemia to end stage renal disease. Complications from surgery include bleeding, incomplete valve resection, urethral stricture or damage to the external sphincter.
Etiology
A genetic cause has not been identified. AUV is postulated to arise either from a tissue growth imbalance during urethral development, incomplete hypospadias, an abortive process during urethral duplication, or faulty union between glandular and urethral tissue.
Diagnostic methods
Diagnosis is with voiding cystourethrogram (VCUG), which typically demonstrates a urethra dilated proximal to the valve and narrowing distal to it. Other findings may include a trabeculated bladder, bladder diverticulum, and urethral diverticulum. On ultrasonography, patients may demonstrate bladder distension and bilateral hydroureteronephrosis.
Differential diagnosis
Differential diagnosis includes posterior urethral valve, prune belly, and urethral atresia.
Antenatal diagnosis
Prenatal ultrasound may identify hydronephrosis, a distended bladder, or periurethral cystic mass which is indicative of the malformation.
Management and treatment
Initial management involves decompression and drainage of the genitourinary system with an indwelling urethral or suprapubic catheter. Definitive surgical treatment is typically with transurethral valve ablation, either with laser, electrocautery or cold knife urethrotomy. However, this may be deferred in favor of a primary vesicostomy in premature infants, or infants with low birth weight and high creatine levels. Due to the risk of developing renal insufficiency and other complications, all patients should be followed up with serial renal and bladder ultrasound. In severe cases with large urethral diverticulum, formal urethral reconstruction is needed, with excision of diverticulum and tubularization of urethra around a catheter.
Prognosis
Delayed treatment can lead to renal insufficiency and is potentially life threatening. Typically, valve ablation results in a good functional outcome, although there is a risk of complications and continued renal or bladder dysfunction.

                            Last update: 
                            September 2020


                            - Expert reviewer(s): 
                            Pr Yazan RAWASHDEH | EUROGEN*


                                * European Reference Network