eMedicine Specialties > Pediatrics: Surgery > Urology

Posterior Urethral Valves: Differential Diagnoses & Workup

Author: Martin David Bomalaski, MD, FAAP, Pediatric Urologist, Alaska Southcentral Urology Specialists
Contributor Information and Disclosures

Updated: Jun 12, 2008

Differential Diagnoses

Antenatal Hydronephrosis
Urinary Tract Infection

Other Problems to Be Considered

Anterior urethral valves
Urethral stricture disease
Detrusor sphincter dyssynergy
Diurnal urinary incontinence
Pediatric renal insufficiency

Workup

Laboratory Studies

• Immediately following birth, the infant's serum chemistries are the same as the mother's. Therefore, serum values for creatinine and BUN should be obtained at least 24 hours after birth. In utero, the placenta functions as the major blood filter for the fetus, with waste passed on to the mother. Observing serum chemistries for several days to weeks is important to determine the true status of the newborn's renal function.
• The normal newborn kidney is still undergoing maturation at birth, and infant glomerular filtration rate (GFR) continues to improve during the first several months of life. Because of renal immaturity at birth, the newborn is unable to concentrate urine and is susceptible to dehydration. This defect is exacerbated by renal dysplasia such as that found with posterior urethral valves (PUVs).
• As renal maturation continues, the serum creatinine clearance normally improves. If significant renal dysplasia or damage has occurred, the serum creatinine fails to reach a normal level during the first year of life. Serum creatinine levels greater than 0.8 mg/dL during the first year of life have been demonstrated to be associated with poor long-term renal function.

Imaging Studies

• Renal and bladder ultrasonography
  • Every child with antenatal hydronephrosis requires renal and bladder ultrasonography assessment in the immediate postnatal period. Focus should be directed towards appearance of the renal parenchyma, evidence of renal collecting system dilatation, bladder wall thickness, and presence of ascites.
  • Because newborns commonly have relative hypovolemia during the first few days of life, perform repeat ultrasonography after the first week of life if previous findings were normal in a child with previously diagnosed antenatal hydronephrosis before making a final determination that the hydronephrosis has resolved (see History).
• Voiding cystourethrography
  • The key to the workup of any child with antenatal hydronephrosis is voiding cystourethrography (VCUG). Perform VCUG during voiding and under fluoroscopy, with imaging of the posterior urethra.
  • The diagnosis of PUV is indicated by visualization of the valve leaflets. Other clues to the diagnosis are a thickened trabeculated bladder, a dilated or elongated posterior urethra, and a hypertrophied bladder neck (see Media files 1-2). Diverticula, cellules, vesicoureteral reflux, and reflux into the ejaculatory ducts secondary to elevated bladder and urethral pressures may also be present (see Media file 2).
• Renal scintigraphy
  • Although not necessary in every child, renal scintigraphy may be helpful in some cases. It should not be performed in the neonatal period because renal immaturity does not allow for accurate estimation of renal function. If renal dysplasia is suspected, nuclear imaging can determine relative renal function. Some children may have secondary ureterovesical junction obstruction due to bladder hypertrophy.
  • Tc-dimercaptosuccinic acid (DMSA), glucoheptonate, and mercaptoacetyl triglycine (MAG-3) renal scintigraphy are cortical imaging studies that provide information about relative renal function (each kidney relative to the other) and intrarenal function (eg, photopenic areas within the kidney indicate scarring or dysplasia). Additionally, the MAG-3 renal scan with furosemide (Lasix) provides information about renal drainage and possible obstruction.

Other Tests

• Urodynamic evaluation provides information about bladder storage and emptying. The mature bladder should store urine at a low pressure and then completely empty at appropriate pressures.
• The term "valve bladder" is used to describe patients with PUV and a fibrotic noncompliant bladder. These patients are at risk of developing hydroureteronephrosis, progressive renal deterioration, recurrent infections, and urinary incontinence.
• Patients with PUV require periodic urodynamic testing throughout childhood because bladder compliance may further deteriorate over time.

Procedures

• Cystoscopy serves both diagnostic and therapeutic functions in these infants. Appropriately-sized cystoscopes (<8F) are needed to avoid injury to the urethra.
  • Diagnostic cystoscopy: Confirmation with cystoscopy is required in every child in whom PUV is suggested after VCUG. In some, the filling defect observed on VCUG may represent only external sphincter contraction during voiding. In others, the valve leaflets are confirmed.
  • Therapeutic cystoscopy (ie, transurethral incision of the PUVs): Multiple techniques have been described for ablating the valves. Disruption of the obstructing membrane by blind passage of a valve hook is now only of historic interest. Currently, valves are disrupted under direct vision by cystoscopy using an endoscopic loop, Bugbee electrocauterization, or laser fulguration. The objective is to relieve the obstruction by cutting the valves at the 12-, 5-, and 7-o'clock positions. Perform this in the least traumatic fashion to avoid secondary urethral stricture or injury to the urethral sphincter mechanism.
• In some patients, the urethra may be too small for the available cystoscopic instrumentation. Fortunately, because of continued advancements in pediatric endoscopic equipment, this is an uncommon occurrence. When this situation arises, a temporary vesicostomy is performed.

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