Prenatal intervention for Fetal Urinary Tract Obstruction

Prenatal diagnosis of fetal urinary tract obstruction requires ultrasound assessment of keyhole sign, bladder thickness, amniotic fluid volume, and fetal sex.

In male fetuses, posterior urethral valves can be diagnosed and are amenable to fetal intervention.

Fetal urinary tract obstruction causes pulmonary hypoplasia due to anhydramnios (insufficient amniotic fluid leading to underdeveloped lungs).

Obstructive nephropathy from urinary tract obstruction creates renal dysplasia, leading to renal insufficiency with associated morbidity, mortality, and need for transplant.

A distended bladder without cycling contractions produces bladder dysfunction with infections and other problems postnatally.

Therapeutic goals for fetal urinary tract obstruction are to restore amniotic fluid (protect lungs), decompress the urinary system (protect kidneys), and allow detrusor cycling (protect bladder function).

Renal function assessment in fetal urinary obstruction is based on bladder tap (fetal urine analysis), ultrasound evaluation of renal parenchyma for cystic dysplasia, and bladder refilling after bladder tap.

Bladder refilling after vesicocentesis demonstrates that the fetus has the ability to make urine.

In severe renal dysplasia where the fetus makes no urine, the only treatment goal is pulmonary survival by replacing amniotic fluid; kidney function cannot be improved.

In moderate or borderline renal dysplasia where kidneys make small amounts of urine, intervention is likely too late to save kidney function but can save the lungs and provide the option of renal transplant.

In cases with no renal dysplasia where kidneys make plenty of urine, decompressive techniques can theoretically rescue both kidney and lung function.

Vesico-amniotic shunt devices commonly used include Rodeck, Harrison, Cook, and Summaex (more common in Europe).

Vesico-amniotic shunt placement has a 98% technical success rate but a 15% complication rate, with complications carrying 100% mortality due to loss of amniotic fluid.

Overall survival with vesico-amniotic shunting is approximately 50%, and of survivors, 40% will develop end-stage renal disease.

Open fetal surgery for vesicostomy was attempted by Crombleholme and Lim in Cincinnati, using minimal uterine exposure to create an abdominal wall opening and marsupialize the bladder for drainage, allowing spontaneous postnatal closure.

In the Cincinnati Children's Hospital series, 6 male fetuses between 19-22 weeks gestational age with anhydramnios and normal fetal urine electrolytes underwent open vesicostomy; all achieved complete postnatal urinary tract decompression, but only 2 of 6 survived, with no maternal complications.

The main technical challenge with fetal cystoscopy for posterior urethral valves is the angulation; while bladder access is good, visualization and orientation of the posterior urethral valves during surgery can be difficult.

Transurethral catheter placement can be combined with laser therapy for posterior urethral valve treatment; in one case at 23 weeks, a wire was used to identify and access valves, followed by laser ablation and transurethral catheter deployment.

For fetuses with kidney dysplasia and minimal urine output who are not candidates for shunt or cystoscopy, the only option is attempting lung rescue by placing fluid from outside to restore amniotic fluid.

Methods for amniotic fluid restoration include repeated serial amnio-infusions with needle (once weekly initially, twice weekly in late gestation) or placement of an amnio-port.

Amnio-port is a metal port used for intravascular medication and parenteral nutrition that can be implanted inside the uterus for easy subcutaneous access to replace amniotic fluid.