Posterior Urethral Valves

Laurence S. Baskin

I. INTRODUCTION

Posterior urethral valves are the most common congenital cause of bladder outlet obstruction, resulting in a spectrum of damage to the entire urinary tract. Valves are obstructing membranes within the lumen of the urethra, extending from the verumontanum distally. They occur only in males (Figs. 15-1 and 15-2). They are the number one congenital cause of renal failure and renal transplantation in the pediatric population.

II. EPIDEMIOLOGY

A. The incidence of posterior urethral valves has been estimated to be approximately 1 per 5,000 to 8,000 male infants, although some recent studies report it to be as common as 1 in 1,250 fetal ultrasounds.

B. There does not appear to be any known ethnic or familial predisposition toward the development of valves.

III. CLINICAL PRESENTATION

The presentations of patients with posterior urethral valves display a wide clinical spectrum depending upon the degree of in utero obstruction. Patients may present prenatally or postnatally.

A. Prenatal Presentation Modern application of prenatal ultrasound examination is responsible for the detection of the majority of posterior urethral valves cases.

1. Prenatal ultrasound features

a. Distended, thick-walled fetal bladder and a dilated posterior urethra (keyhole sign).

b. Hydronephrosis: This can be due to bladder outlet obstruction and/or the presence of vesicoureteral reflux.

c. Oligohydramnios: An assessment of the amniotic fluid volume is an important prognostic indicator. Since most of the amniotic fluid volume depends upon fetal urine production after 16 weeks, oligohydramnios is an indication of either poor fetal renal function or bilaterally obstructed kidneys. Severe oligohydramnios predisposes the infant to Potter’s syndrome and pulmonary hypoplasia. The timing and degree of oligohydramnios play an important role in the severity of postnatal outcomes. Patients diagnosed with posterior urethral valves and oligohydramnios before 24 weeks’ gestation have a poor prognosis.

2. Prenatal intervention: Prenatal diagnosis of posterior urethral valves has allowed pediatricians and pediatric urologists an opportunity to plan for and initiate treatment immediately after birth.

Although some authors had expressed initial enthusiasm with in utero treatment of valves by the placement of a vesicoamniotic shunt or fetal open surgery, there is now little evidence to suggest a favorable risk to benefit ratio in terms of the preservation of renal or bladder function. Similarly, early delivery has failed to show significant benefit.

FIG. 15-1 Schematic of posterior urethral valves. Obstructing valve is seen in the dilated posterior urethra at the bottom of the diagram (black arrows). Note the thickened bladder and bilateral hydroureteronephrosis.

FIG. 15-2 Schematic of sagittal view of posterior urethral valve with catheter placed to the level of the obstructing valve/membrane (black arrow).

B. Postnatal Diagnosis

Postnatal diagnosis may occur either immediately postnatally or may be delayed several years owing to the wide spectrum of the disease and its manifestations.

1. Respiratory distress: Infants with severe oligohydramnios will usually present immediately postnatally due to the consequences of life-threatening pulmonary hypoplasia.

2. Sepsis and azotemia: The most severely affected infants may also present in the neonatal period with fulminate sepsis and azotemia, due to long-standing obstruction and renal dysplasia.

3. Abdominal distention: In the neonatal period, the presence of valves is suggested by the finding of a palpable distended bladder. The presence of urinary ascites or markedly distended upper tracts can also result in a tensely distended abdomen.

4. Voiding dysfunction: Some neonates may have difficulty in generating a normal urinary stream or fail to void during the first 48 hours of life. In rare cases, less severely affected patients may present during early childhood with incontinence or recurrent infections. Abnormalities in voiding dynamics and bladder compliance are responsible for the persistence of what is commonly called the “valve bladder syndrome,” a condition manifested by a spectrum of bladder and renal dysfunction.

IV. INITIAL MANAGEMENT OF POSTERIOR URETHRAL VALVES

Once the diagnosis of posterior urethral valves is suspected, the first step in the management often consists of the stabilization of acute illness (Fig. 15-3). The patient should be medically stabilized as much as possible before proceeding with urologic evaluation and treatment.

A. Acute Illnesses Associated with Posterior Urethral Valves

1. Respiratory distress

2. Sepsis

3. Dehydration

4. Electrolyte abnormalities