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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.
Since 2004, we have evaluated more than 175 patients for fetal BOO / PUV.
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 in the kidneys (hydronephrosis) and in severe cases, a deficiency of amniotic fluid (oligohydramnios) that can threaten lung development.
The effects in children born with bladder outlet obstruction range from completely asymptomatic to 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 neonatal death.
In most cases, bladder-outlet obstruction due to posterior urethral valves is a sporadic event. In rare cases, it is associated with a chromosomal abnormality, which increases the risk of a subsequent fetus being affected.
Posterior urethral valves account for 10 percent of all urologic anomalies detected by prenatal ultrasound. It is estimated, however, that prenatal ultrasound detects only 50 percent of new cases of posterior urethral valves, suggesting that the incidence of posterior urethral valves is 1 in 4,000 live births. This estimate does not take into account cases where pregnancy does not end in live birth or asymptomatic cases discovered later in life.
Posterior urethral valves can be diagnosed by ultrasound (sonogram) before birth. In mild cases, the fetus may have obstruction in the urinary tract, but with amniotic fluid volume maintained, minimal changes in the bladder and ureters, and no dysplasia in the kidneys. In severe cases, the fetus has profound oligohydramnios, distended bladder and ureters, and dysplastic changes in the kidneys.
Sonographic findings indicating bladder obstruction include a thickened bladder wall and if posterior urethral valves are the cause, the posterior urethra will also be dilated. Along with a detailed examination of the urinary tract itself, the sonographic evaluation should look for amniotic fluid volume and the presence or absence of ascites (fluid in the abdomen).
Oligohydramnios is a sign of high-grade obstruction and over time can lead to pulmonary hypoplasia as well as other deformations, such as club feet and "Potter facies," which results from facial decompression against the uterine wall. The increased incidence of these other malformations means that the fetus should also be scanned for them.
Ultrasonographic examination of the fetal kidneys may provide prognostic information. Fetuses with bilateral hydronephrosis and normal amniotic fluid may not need intervention and fetuses shown by ultrasound to have bilateral hydronephrosis, severe oligohydramnios, and severe dysplasia in the cortex of the kidney are unlikely to benefit from in utero therapy.
For fetuses in between these two extremes of not needing or not being likely to benefit from in utero therapy, prognostic criteria are the most important and sensitive means of assessing fetal renal function essential to making treatment decisions. In addition to the evaluation of the fetal urinary tract, an assessment of the overall growth and development of the fetus will be conducted.
The use of serial sampling of fetal urine and chromosomal analysis has significantly improved the predictive value of testing to identify fetuses with significant renal damage. Echocardiography should be performed to 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 outcome.
We have achieved a 61 percent survival rate* (to 30 days) for patients who underwent fetal interventions to treat BOO / PUV.
Total of eight amnioports have been performed as an adjunct therapy for BOO / PUV and other GU anomalies.
*Feb. 1, 2004, through June 30, 2012
Illustration of bladder outlet obstruction.
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