Lower urinary tract obstructions (LUTO), also known as obstructive uropathy, are rare birth defects that occur in 1 in 5,000 to 7,000 births, commonly in male fetuses. LUTO is caused by a blockage of fetal urination.
Because the baby cannot empty the bladder, the baby’s bladder subsequently becomes very large and swollen. Also, because the amniotic fluid is essentially composed of the baby’s urine beyond the middle of the second trimester, the bag of waters dries up. Secondary effects can result in problems to the urinary collection system (hydronephrosis) and kidneys (renal dysplasia), underdevelopment of the lungs (pulmonary hypoplasia) and even death.
Urinary tract obstructions come in a variety of forms:
- Urethral atresia (UA) — a complete obstruction of the urethra
- Posterior urethral valves (PUV) — a flap of tissue blocking the urethra
- Triad syndrome — a constricted narrowing in the mid-portion of the urethra which results in a highly restricted ability for the urine to pass.
The prognosis for each individual case depends upon the underlying cause and severity of the obstruction as well as the presence or absence of other findings. Fetal urine is an important component of amniotic fluid during gestation and contributes to fetal lung development.
Early diagnosis and intervention are essential. A diagnosis of LUTO is usually made by ultrasound in the mid-second trimester.
A thorough prenatal evaluation will determine whether or not your baby may benefit from fetal intervention. The presence of cysts in the fetal kidneys on initial ultrasound is an indicator of irreversible kidney damage. In these cases, fetal intervention will not improve the outcome and is thus not performed. An enlarged fetal bladder with normal amniotic fluid volume indicates an incomplete obstruction. These cases are typically followed by ultrasound until amniotic fluid levels decrease.
Upon completion of the evaluation, our multidisciplinary team meets with your family to review test results, discuss the diagnosis, explain treatment options and potential outcomes, and answer questions.
For fetuses with a favorable prognostic, treatment is predominantly aimed at restoration of amniotic fluid volume.
Male fetuses with isolated complete obstruction that show serial improvement in urine electrolytes (indicating salvageable kidney function) and no other genetic or chromosomal abnormalities may be candidates for fetal intervention via vesicoamniotic shunt placement.
A shunt is a hollow tube that temporarily bypasses the lower urinary tract obstruction and provides an alternate passageway for urine to go from the bladder through the abdominal wall to the amniotic fluid space around the fetus. This allows for drainage of the urinary tract and bladder and establishes fluid around the fetus, which is necessary for lung development.
After the procedure, expectant mothers receive antibiotics and are monitored for any post-procedural complications.
After post-procedural follow-up, mothers who have undergone prenatal surgery return home and are monitored by their local care team.
After your baby is born, pediatric urologists and nephrologists (kidney doctors) will evaluate your child's condition, the team will counsel your family on what to expect in both the short- and long-term.
Postnatal treatment options depend on the type of obstruction. For posterior urethral valves (PUV), endoscopic resection (valve ablation) is a minimally invasive technique performed within the first several days of life, along with the removal of the shunt. Urologic surgeons attach specialized surgical instruments to a tool with a light and camera (endoscope) and insert it into the urethra to remove the tissue (valves) causing the obstruction.
In more complicated cases, a vesicostomy — an opening below the belly button that allows the bladder to drain directly into a diaper — diverts urine until the baby is healthy enough to undergo valve resection or urethral reconstruction.