Congenital membranes obstructing the posterior urethra are called posterior urethral valves.
Three types have been classified:
- Type 1. Valves representing folds extending inferiorly from the veru to the membranous urethra.
- Type 2. Valves as leaflets radiating from the veru proximally to the bladder neck.
- Type 3. Valves as concentric diaphragms within the prostatic urethra, either above or below the veru.
By far the most common are Type 1 valves, and these are believed to result from failure of the posterolateral migration of the urethrovaginal folds, with fusion of the distal (or anterior) extension of these folds.
Posterior urethral valves may present with a broad array of symptoms or signs at any age during childhood and may vary from ascites in the neonate to renal failure in an infant or only minor voiding dysfunction in an older child. Urinary tract infection is common at all ages.
Inability to void is a common presentation.
Voiding normally occurs on the first day after birth, but about 3% of normal babies wait 48 hours to initiate urination.
Other infants present because of a thickened palpable bladder that remains palpable after voiding or because of palpable flank masses.
Urinary ascites is common, and urinary extravasation is usually from the renal fornices.
Urethral valves may also present as neonatal hematuria because of the trauma of delivery on the hydronephrotic upper tract.
Diminished urinary output in utero usually results in oligohydramnios. This can also lead to pulmonary hypoplasia and respiratory distress syndrome. Spontaneous pneumothorax or mediastinal air is common when respiratory distress is present.
Generally, a poor outcome is seen when a mother shows oligohydramnios and a fetus shows hydronephrosis.
Associated with this dysfunction may be renal dysplasia, which may compromise renal function despite relief of obstruction. Furthermore, changes in bladder morphology and histology secondary to the chronic obstruction may also compromise bladder function despite relief of obstruction.
The bladder muscle or detrusor is often very thickened, leading to ureteral obstruction and at other times reflux. Also, the bladder neck may be very thickened, leading to outflow obstruction. Children with secondary bladder neck obstruction may require relief of this problem through bladder neck incision, but this can give rise to retrograde ejaculation later and possible infertility.
Depending on the degree of obstruction, azotemia, acidosis, hyponatremia, hypertension and at times hyperkalemia may be seen.
Urinary tract infection may present at any time and cause a life-threatening situation.
Older infants and children usually have less renal function impairment and may present with a urinary tract infection or various voiding problems such as urgency, frequency or incontinence.
In some older children, because of chronic obstruction and poor emptying, clean intermittent catheterization may be required to empty the bladder, despite relief of obstruction.
The diagnosis is made radiologically with a voiding cystourethrogram (VCUG). This is usually done in conjunction with the renal ultrasound to evaluate the upper tracts.
Renal function studies, in addition to serum studies, should determine the glomerular filtration by clearance values and some estimation made of urinary concentrating ability. It is important to remember that the GFR of a normal, healthy infant (corrected for surface area) is significantly less than that of a healthy young adult.
Most neonates and young infants present with significant reduction in renal function and moderate degrees of acidosis, hyponatremia and dehydration.
In order to assess the potential for renal recovery, catheter drainage with a small feeding tube is usually done for 3-7 days during correction of acidosis and rehydration.
If renal function improves satisfactorily, a vesicostomy or, if the urethra is large enough, a transurethral procedure may be accomplished; and a wait-and-see approach is taken regarding the hydronephrosis and/or reflux.
In patients whose condition continues to deteriorate following a vesicostomy, some type of supravesical drainage can be established as a secondary procedure. Loop ureterostomy or pyelostomy may be options.
Vesicoureteral reflux is seen in about 1/3 of children, and the decision regarding reimplantation of ureters should be done, as it should in any child with primary reflux.
Most fatalities occur because of underlying renal dysplasia.
Some children with minimal renal reserve eventually develop renal failure and require transplantation.
Urinary incontinence and/or urethral stricture problems are also common. Tofranil can help the incontinence if the child is older. Bladder neck obstruction is common in association with urethral obstruction. Bladder neck obstruction may be diagnosed if residual urine, trabeculation, reduced flow rate, or elevated resting and voiding bladder pressures are present after residual valves and detrusor sphincter dyssynergia have been excluded. Bladder neck tone may also be reduced by Minipress or a bladder neck incision.