Rigi10™ Malleable Penile Prosthesis
Also Known As
Posterior Urethral Valves, PUV, Congenital Obstructing Posterior Urethral Membrane, CO PUM.
Definition
Posterior urethral valves (PUV) are the most common cause of bladder outlet obstruction in male infants and a significant cause of chronic kidney disease originating from obstructive uropathy in the pediatric population.¹ They are congenital, abnormal membranous folds located within the posterior urethra, typically attached to the verumontanum, which is a landmark in the prostatic urethra. These folds obstruct the normal urine flow from the bladder out of the body.¹ The obstruction can lead to a wide spectrum of clinical manifestations, ranging from mild voiding difficulties to severe urinary retention, renal failure, and even pulmonary hypoplasia secondary to decreased amniotic fluid levels in utero if the obstruction is severe.¹ The primary purpose of identifying and treating posterior urethral valves is to relieve this urinary tract obstruction, thereby protecting bladder and kidney function, and improving the overall long-term outcomes for affected individuals.²
These valves are classified into three main types based on Young’s criteria, which describe the orientation of the valve leaflets within the urethra. Type I valves, accounting for approximately 95% of cases, consist of mucosal folds that extend inferiorly and anteriorly from the verumontanum to the membranous urethra. Type II valves are described as folds extending superiorly from the verumontanum towards the bladder neck, but their existence as a true obstructing entity is debated, and they are now often considered hypertrophic plicae colliculi. Type III valves are a diaphragm or ring-like membrane with a central opening, located either above (Type IIIa) or below (Type IIIb) the verumontanum, though this type is rare.6
The mechanism by which these valves cause obstruction involves the flap-like nature of the tissue. During voiding, the flow of urine pushes these membranous folds, causing them to appose and occlude the urethral lumen, thus increasing intravesical pressure and leading to a cascade of secondary changes in the bladder and upper urinary tracts, such as bladder wall hypertrophy, trabeculation, diverticula formation, vesicoureteral reflux, and hydroureteronephrosis.¹³
Clinical Context
Posterior urethral valves (PUV) are typically diagnosed in male infants or young children, often presenting with a spectrum of urinary symptoms or complications arising from bladder outlet obstruction.¹ The clinical context for PUV encompasses antenatal detection, neonatal presentation, and later diagnosis in childhood. Antenatally, routine maternal ultrasonography may reveal findings suggestive of PUV, such as a distended bladder with a thickened wall, bilateral hydroureteronephrosis (dilation of the ureters and kidney collecting systems), and oligohydramnios (low amniotic fluid).¹ The presence of a “keyhole sign” on ultrasound, representing a dilated posterior urethra and bladder, is a classic indicator, though not exclusively diagnostic for PUV.¹ Early antenatal detection is crucial as it allows for parental counseling and planning for postnatal management, although in-utero intervention is rarely performed and remains investigational.¹
Neonatal presentation can vary widely. Some infants may be asymptomatic initially, while others present with signs of severe urinary obstruction, including a weak urinary stream, straining to void, a palpable bladder, or urinary retention requiring immediate catheterization.¹ Respiratory distress can also be a presenting feature in severe cases due to pulmonary hypoplasia secondary to prolonged oligohydramnios.¹ Urinary tract infections (UTIs) are common in infants with PUV and may be the first indication of an underlying abnormality.¹ Failure to thrive, electrolyte abnormalities, and signs of renal insufficiency (e.g., elevated creatinine) can also be observed in the neonatal period if the obstruction has led to significant kidney damage.¹³
Patient selection criteria for intervention are straightforward: any male infant or child with a confirmed diagnosis of PUV requires surgical ablation of the valves to relieve the obstruction.¹ The gold standard for diagnosis is a voiding cystourethrogram (VCUG), which visualizes the dilated posterior urethra and the valve leaflets during voiding.¹ Cystoscopy can also be used for direct visualization and is often performed concurrently with valve ablation.¹
The primary surgical procedure is transurethral valve ablation, where an endoscope is passed through the urethra, and the obstructing valve leaflets are incised or fulgurated.¹ This procedure aims to create an unobstructed channel for urine flow. In very small infants or those critically ill, a temporary urinary diversion, such as a vesicostomy (an opening from the bladder to the abdominal wall), may decompress the urinary system before definitive valve ablation.¹
Expected outcomes after valve ablation are variable and depend on the severity of the obstruction and the degree of pre-existing renal and bladder damage.¹ Many boys experience significant improvement in urinary flow and reduced hydronephrosis. However, a substantial proportion may develop long-term complications, including chronic kidney disease (CKD), bladder dysfunction (often termed “valve bladder syndrome”), vesicoureteral reflux, recurrent UTIs, and voiding difficulties such as incontinence.¹³ Valve bladder syndrome is characterized by a poorly compliant, high-pressure bladder that can contribute to ongoing upper tract deterioration even after valve ablation.6 Long-term urological and nephrological follow-up is essential for all boys with PUV to monitor kidney function, bladder dynamics, and manage any ensuing complications. Approximately one-third of boys with PUV may eventually progress to end-stage renal disease requiring dialysis or kidney transplantation.¹