Bladder Obstruction
Open Fetal Surgery for Bladder Outlet Obstruction Due to Posterior Urethral Valves
Posterior urethral valves are the most common cause of bladder outlet obstruction in males. An abnormal fold of tissue in the urethra blocks urine from flowing freely out of the bladder. If not corrected, this blockage can cause backup of urine in the bladder, the ureters and kidneys and in severe cases, a deficiency of amniotic fluid (oligohydramnios) that can threaten lung development. In most cases, the specific cause is not known. In rare cases, the condition is linked to a genetic abnormality, which increases the risk to a subsequent fetus.
Children born with bladder outlet obstruction may have no symptoms or have multiple symptoms, including respiratory insufficiency at birth as a result of pulmonary hypoplasia (arrested development in the lungs) and kidney failure from renal dysplasia (abnormal development of the kidneys). Severe respiratory insufficiency at birth is a leading cause of death.
Diagnosing Bladder Outlet Obstruction
Posterior urethral valves can be diagnosed by ultrasound (sonogram) before birth. In addition to evaluating the fetal urinary tract, overall growth and development of the fetus is assessed. Sampling of fetal urine and chromosomal analysis improved the ability of testing to identify fetuses with significant kidney damage. Echocardiography can rule out structural heart disease. Consultations with a genetics counselor and pediatric specialists in urology, nephrology and neonatology can be helpful in learning about treatment options and long-term outcomes.
Fetal Therapy
Before therapy begins, all test results and other assessments of the fetus and mother are reviewed to understand how a prenatal condition would progress if left untreated. Fetuses most likely to benefit from fetal intervention are those with obstruction severe enough to compromise kidney and lung development, but not so severe that kidney damage is irreversible. The challenge lies in selecting which fetuses should have prenatal intervention to prevent ongoing damage, be delivered early to prevent ongoing kidney damage, and should go to term and be treated after birth.
Fetal Interventions
In utero interventions are intended to decompress the urinary tract, restore amniotic fluid and prevent neonatal death due to failure of the lungs and/or kidneys to develop properly. Available fetal interventions are vesicoamniotic fetal shunting, fetoscopic surgery and open fetal surgery.
Vesicoamniotic Fetal Shunting
Vesicoamniotic shunting drains urine from the bladder into the amniotic space. This procedure has the advantage of bypassing the obstruction, but does not completely decompress the urinary tract. It has the risk of complications, including inflammation of the fetal membranes. Shunts may become obstructed or displaced. Functional shunt failure has been reported to occur in 40% to 50% of cases after successful placement of the shunt. Survival following shunting ranges from 40% to 85%.
Fetoscopic Surgery
In fetoscopic surgery, surgeons use a fiberoptic endoscope to enter the uterus and correct defects through small surgical openings. This minimally invasive procedure is in its infancy and is limited to very few patients. Posterior urethral valves are among the fetal malformations treatable by fetoscopic techniques.
Several small studies have shown that fetoscopic cystoscopic laser treatment (using a fetoscope to inspect and pass instruments into the bladder and urethra) can be used to treat bladder obstruction due to posterior urethral valves. The fetoscopic approach, with its small puncture sites, could reduce the risks of preterm labor, hemorrhage, amniotic fluid leak, and uterine rupture and eliminate the need for cesarean delivery following fetal surgery. Despite the compelling rationale for fetal cystoscopic treatment and advances in fetoscopic techniques, this approach has yet to be shown to be a generally safe and effective treatment for posterior urethral valves.
The fetoscopic approach is limited to patients with 20 or fewer weeks gestation and posterior urethral valves and oligohydraminos. In addition, patients must have a favorable prognosis based on fetal urine electrolytes and imaging studies, such as ultrasound and magnetic resonance imaging (MRI).
Open Fetal Surgery
The Fetal Care Center of Cincinnati uses open fetal surgery as the most definitive means of decompressing the urinary tract to prevent ongoing injury to the developing kidney. In this procedure, the fetal abdomen is opened below the umbilical cord insertion and then the bladder is opened and sutured to the fetal skin. This allows complete urinary diversion and eliminates high bladder pressure seen with vesicoamniotic shunts.
While this is a much more invasive approach with greater potential risk to the mother and fetus, preliminary experience is encouraging, with normal bladder functioning for the baby. The baby is usually born prematurely, however, and the mother will need to deliver by cesarean section because of the scar created by the surgery.
Open fetal surgery is a therapeutic innovation being offered at the Fetal Care Center of Cincinnati for fetuses with posterior urethral valves and favorable prognosis with oligohydraminos. Long-term follow-up studies are needed to prove this approach is superior to shunting and that the improved outcome is substantial enough to warrant increased fetal and maternal risks.
