Although obstruction to urinary outflow in boys is sometimes obvious, many times the signs and symptoms are so vague that the diagnosis is very difficult to make. Posterior urethral valves are the most common cause of bladder outlet obstruction in children. The long-term consequences of such obstruction, including decreased renal function and infection, remain serious problems for some patients despite newer methods of diagnosis and treatment.
ANATOMY AND EMBRYOLOGY
The male urethra extends from the bladder neck to the meatus at the tip of the penis. The anterior urethra includes the bulbous and penile portions. The posterior urethra consists of the first few centimeters distal to the bladder neck, including the prostatic urethra and the membranous urethra where the external sphincter resides. Located in the posterior midportion of the prostatic urethra is the verumontanum, containing the paired ejaculatory duct openings and the miillerian remnant known as the prostatic utricle. Extending inferiorly from the verumontanum in the midline is the crista urethralis, and diverging from this are the plicae colliculi, which merge into the external sphincter/membranous urethra area as two oblique folds. These plicae may be normal remnants of the terminal wolffian ducts, which regress during embryogenesis, leaving only the ejaculatory duct openings.
It is postulated that abnormal formation or regression of the plicae may be involved in the genesis of typical posterior urethral valves, which are exaggerations of the normal folds. ' Beginning at the verumontanum and extending toward the membranous urethra, they swing laterally and upward to meet in the twelve o'clock position at the anterior wall just proximal to the membranous urethra. The appearance endoscopically is that of two membranes, paired in a manner similar to the vocal cords, fused anteriorly. This fusion creates a valve which obstructs the outflow of the urine while allowing the retrograde passage of catheters or irrigating fluid.
Valve descriptions based upon Young's original classification (1919) (Types I, II, III) are not helpful today. Ninety-five percent of posterior valvular obstructions are of Type I, with variations in leaflet thickness, and in the degree of coalescence at the twelve o'clock position. The resulting obstruction can consist of filmy membranes which are easily disrupted, or, at worst, a thickened tissue layer with a small inferior opening. The other 5% of valvular obstructions consist of congenital urethral membranes, which are obstructing diaphragms with a central opening, located in the membranous urethra (Type III). These do not have a typical attachment to the inferior portion of the verumontanum, and probably are of a different embryologie origin.
Figure 1A. Newborn with typical urethral valvular obstruction (voiding cystogram).
In the past, half of the children with posterior urethral valves presented in the first six months of life. Today, prenatal ultrasound allows diagnosis of these cases before clinical signs and symptoms are present.
The nature of the problem will occasionally be very clear, with a palpably distended bladder or palpable hydronephrotic kidneys associated with a dribbling urinary stream. However, in many more cases, the diagnosis is not obvious because the child has no noticeable abnormalities of the urinary stream. These children can present with urinary tract infection or sepsis, or simply a failure to thrive. Older children will more typically present with urinary tract infection or mild voiding abnormality. It is very rare for pure nocturnal enuresis to be the presenting complaint with urethral valves. It is logical that the more severely obstructed infant will present sooner due to renal compromise. However, even these babies may be 6 to 12 months old before the diagnosis is made. Suspicion of the diagnosis can be confirmed with a simple ultrasound. Sonography has rapidly become the most important tool in the screening and initial diagnosis of this condition. Anatomic information concerning bladder size and bladder wall thickness, posterior urethral distention, hydroureteronephrosis, and size and character of the renal parenchyma are information that can be gained from ultrasound. Confirmation of the diagnosis rests with a voiding cystourethrogram demonstrating typical features of the posterior urethral obstruction. These features include prostatic urethral distention with a typical ballooning at the level of obstruction, prominence of the verumontanum as a negative shadow, hypertrophy of the bladder neck with bladder trabeculation and, in 50% of cases, reflux to one or both kidneys.
Figure 1B. Intravenous pyelogram before valve ablation.
Initial therapy should be based upon treatment of infection and stabilization of electrolyte abnormalities. Many of the neonates present with significant acidosis, hyperkalemia, and azotemia, which must be controlled prior to any definitive surgery to relieve the obstruction. In addition, urinary tract infection or sepsis must be treated aggressively. Usually these problems may be managed with placement of a small (5 or 8 F) plastic feeding tube per urethra so that urinary drainage may be achieved. At the same time, broad spectrum antibiotic coverage should begin and be modified according to the results of initial culture. Even without infection, antibiotics should be used. At the same time, electrolyte abnormalities are corrected. Although the initial serum creatinine level may be quite high, remarkable recovery is often achieved with these simple measures. It is not uncommon for creatinine as high as 6 mg/dL to drop to the near normal range within a few days. The achievement of a normal serum creatinine within the first months after treatment portends a good long- term renal prognosis with these children.2,3
Figure 1C. Two months after valve ablation (voiding cystogram).
Once the child's overall medical condition is optimized and infection controlled, attention can be directed toward more definitive treatment of the obstruction. Direct ablation of the obstructing valvular tissue followed by careful scrutiny of renal function recovery is the best treatment in the majority of cases. Typically, this is carried out transurethrally in a retrograde manner to directly ablate the valve at the critical junction points with the urethral wall. This may be either solely at the twelve o'clock position or at five, seven, and twelve o'clock positions. Care is taken to avoid injury to the urethral wall or external sphincter during this procedure. Although the occurrence of postoperative strictures has been noted by some authors, in our recent review this was not a significant problem. Aggressive endoscopic treatment is avoided. Incomplete destruction in the first instance may require a second procedure in 15% to 20% of cases (Figure 1).
Figure ID. Intravenous pyelogram after valve ablation alone.
Infants with a urethra that is too small to permit the passage of an endoscope are very adequately decompressed with a vesicostomy for the first year or two of life. This bypasses the obstruction and allows good drainage of the thickened bladder and dilated upper tracts. This form of tubeless drainage requires no additional care by the parents once adequate healing has taken place, and is easily reversible when the child has grown enough to permit valve ablation. Our experience with children under the age of 6 months shows that about 20% required management with a vesicostomy. Use of a long-term catheter to drain the bladder is known to be detrimental.
After either primary valve ablation or vesicostomy, the patient must be monitored for infection and electrolyte abnormalities. The child who does not improve clinically within the first week or two after initial management requires further assessment with ultrasound and renography, which may indicate the need for further upper tract diversion. In these rare instances (13% in our series), a high ureterostomy or pyelostomy affords optimal drainage of the upper system. In addition, bilateral renal biopsy will permit some estimate of functional capabilities. In all of our high diversions, severe renal dysplasia has been present. Only three of the eight still survive.
The optimal result of any of these approaches is a child who is free from any point of obstruction so as to optimize renal recoverability and to maintain sterile urine. Unfortunately, the ultimate outcome depends upon the degree of renal development that occurred in the first trimester of gestation.
Figure 2. VURO (Valves. Unilateral Reflux, Dysplasia). Gross reflux, left side, with nonfunction demonstrated on renal scan. Nephroureterectomy performed; dysplasia confirmed.
Vesicoureteral reflux is seen in approximately 50% of children with posterior urethral valves. After definitive treatment of the obstruction, spontaneous resolution of reflux can be expected in about 25% of refluxing cases. This may occur up to three years following valve ablation or vesicostomy. Children without spontaneous resolution are given prophylactic medication and carefully monitored for evidence of urinary infection or poor renal growth. Antireflux surgery in babies is rarely required (20% in our experience).
There is a subset of children with reflux who have been identified as having the VURD syndrome (Figute 2). This problem is characterized by valves and unilateral vesicoureteral reflux to a nonfunctioning kidney which shows histologic evidence of renal dysplasia. Spurious function in the refluxing side is deceiving in delayed intravenous pyelogram films. Nephroureterectomy on the affected side is often a good choice when nonfunction is confirmed by radionuclide renal scan with a catheter in the bladder. Removal of this reservoir for infection will also improve voiding dynamics, because urine can no longer escape into the dilated segment.
Some children (25%) who have been adequately treated early in life will be found at ages 5 to 15 years to have persistent upper urinary tract dilatation without true obstruction on diuretic renography. In these children, there seems to be a physiologic obstruction at the ureterovesical junction associated with bladder filling, but this is not a true anatomic obstruction. A full bladder in these boys is not perceived as uncomfortable. We have labeled this the Full Valve Bladder Syndrome (FVB). Surgical intervention to reimplant ureters is not helpful. Many of these children will decompress the upper tracts if trained to empty their bladders adequately by the clock (every four hours) along with double voiding (five minutes apart) twice a day. The urinary stasis that occurs in the upper tracts will abate with regular bladder emptying and improve both the appearance of the upper tracts on x-ray and the renal function as measured by serum creatinine. If this foils, a program of clean intermittent catheterization may be required. This will allow complete emptying of the system at regular intervals, thus achieving the goal of complete decompression and better recovery of muscular function in the ureters and bladder. Twice daily catheterization usually suffices for this purpose; mandating more frequent drainage will often lead to noncompliance, especially in adolescents.
Urinary incontinence which persists through childhood has also been a problem in some of these children. Early reports indicated that a high percentage of children had varying degrees of stress incontinence.4 Most children with this problem had been treated earlier with bladder neck resection in a mistaken attempt to rid the patient of supposed additional obstruction at the hypertrophied neck. We now know that the muscular hypertrophy at this region is secondary to the more inferior valvular obstruction and is part of the overall detrusor thickening. It is rarely a cause of true obstruction. Since this has been discovered and bladder neck resections have been discontinued, stress urinary incontinence has not been a significant problem. A review of patients followed up to 15 years following valve ablation shows that although 30% may have some kind of wetting, it does not seem to be due to sphincter damage. Rather, it is associated with bladder instability, inadequate attempts to empty the bladder completely,5 or due to polyuria from a tubular concentrating defect. Spontaneous improvement in urinary continence occurs around puberty; perhaps prostatic growth has something to do with this. In our hands, external sphincter damage at the time of primary valve ablation has not been a complication of early (neonatal) treatment, nor has the use of perineal urethrostomy led to stricture problems later.
The early mortality rate for this disease has dropped significantly in the last 10 to 15 years, but little progress has been made with regard to long-term renal function, despite our improved surgical approaches. Up to 35% of children with posterior urethral valves will develop some degree of chronic renal failure (creatinine level > 2 mg/dL). The children who seem to do better are not distinguished by a particular set of anatomic or demographic characteristics. However, it has been shown that the stabilization level of creatinine within the first few months of life is the most important prognostic factor for these children.2, 3 A creatinine of 1 or less within the first month after definitive drainage, regardless of the original creatinine, has generally meant good long-term renal function as measured by serum creatinine and normal somatic growth velocity. Some of the children with previous valvular obstructions persist with a tubular concentrating defect which results in high urinary outputs.
In contrast to children who respond well to initial therapy, end stage renal disease in the infant is a difficult problem. The choice for early aggressive treatment, ultimately leading to renal transplantation, requires skilled pediatric nephrology, urology, and surgery services. There are practical problems with choosing optimal methods of dialysis, maintaining good growth rates, and establishing experience with infant renal transplantation. Many of the answers to these problems are empiric, because our understanding of the metabolic derangements (ie, renal osteodystrophy and growth) is limited. In addition, the financial and social costs of treatment to the patient, family, and community must be considered.6
Continuous ambulatory peritoneal dialysis has emerged as a practical treatment for even tiny infants with end stage renal disease. The incidence of peritonitis using this method is 1.7 episodes per patientyear, which is similar to the adult experience. In certain centers, renal transplantation is being carried out in children weighing only 10 kilograms with acceptable success. Growth, however, is still a problem.
The place of prenatal intervention for urethral valves has yet to be fully determined. Attempts at specific indications for such treatment are being defined in both human and animal studies. However, this work should currently be considered experimental. Harrison's7 incredible human experiment was most convincing to us that fetal intervention will not be the solution. His team diagnosed urethral valves at 21 weeks gestation, intervened with a hysterotomy, accomplished bilateral loop ureterostomies and carried the fetus to near term. Unfortunately, the baby died with pulmonary hypoplasia and severe renal dysplasia. (Further details on this subject are covered in the article by Elder and Duckett, Management of the Fetus and Neonate with Hydronephrosis Detected by Prenatal Ultrasonography ).
1. Stephen» FD (ed): Congenital intrinsic lesiuns of the posterior urethra, in Congenital Malformations of the Urinary Traxt. New York, Praeger Publishing Co, 1983. pp 95-125.
2. Duclcett JWi Management of posterior urethral valves. AUA Weekly Update Series 1983; 2: Lesson 38.
3. Watshaw BL, Hyroes LC. Trulock TS, et ah Prognostic features in infants with obstructive uropathy due to posterior urethral valves. J UnH 1985; 133:240.
4. Whifaker RH, Keeton JE, Williams Dl: Posterior urethral valves: A study of urinary amtrol after operation. J Urol 1972; 108:167.
5. Bauer SB, Dieppa RA, Labib KK, et al: The bladder in boys with posterior urethral valves: A urodynamic assessment. J Urol 1979; 121:769.
6. Fine RN, Gruskin AB: End Stage Renal Disease in Children. Philadelphia, WB Saunders Gi, 1984.
7. Harrison MR, Golbus MS. Filly RA. et al: Fetal surgery for congenital hydronephrosis. N Engl J Med 1982; 306:591.