Fetoscopic Meningomyelocele Repair Study

Spina bifida can be a devastating neurological congenital anomaly . It results from incomplete closure of the neural tube between 22 and 28 embryological days. Its incidence is approximately 1-2 per 1,000 births. It is considered the most common congenital anomaly of the central nervous system that is compatible with life.

1. The most frequent form is myelomeningocele (MMC), characterized by the extrusion of the spinal cord into a sac filled with cerebrospinal fluid (CSF), and is associated with lower limb paralysis and bowel and bladder dysfunction.

2. The majority of MMCs can be diagnosed between 14 and 20 weeks of gestation. MMC is associated with Chiari II malformation, which includes a constellation of anomalies such as hindbrain herniation, brainstem abnormalities, low-lying venous sinuses and a small posterior fossa.The Chiari II malformation can have deleterious effects on motor, cranial nerve and cognitive functions. Postnatally most MMC patients develop hydrocephalus and require a ventriculoperitoneal shunt. Shunts require lifelong monitoring and have a high failure rate due to infection, obstruction, and fracture.

Experimental studies using animal models have shown that prenatal coverage of a spina bifida-like lesion can preserve neurological function and reduce or reverse hindbrain herniation.These studies suggest a "two-hit" hypothesis in which the ultimate neurologic deficit results from a combination of the failure of normal neural-tube closure (first hit) with secondary spinal cord injury resulting from prolonged exposure of sensitive neural elements to the amniotic fluid (second hit mechanism).

Based on this hypothesis, open fetal surgical repair of MMC was proposed, and the recent publication of the NICHD sponsored randomized controlled trial demonstrated clear neonatal benefit of open in-utero fetal surgical repair of MMC. The study showed a reduction in the incidence of hydrocephalus and in the radiographic severity of hindbrain herniation (relative risk: 0.67; 95% confidence interval: 0.56-0.81).

Open in-utero fetal surgery is not without risk and the NICHD study (MOMS Trial) showed an elevation in maternal-fetal morbidity/risk when compared to the postnatally treated group, including higher risk for chorioamniotic separation (26% vs. 0%, respectively), maternal pulmonary edema (6% vs. 0%), oligohydramnios (21% vs. 0%), placental abruption (6% vs. 0%), spontaneous membrane rupture (46%; RR: 6.15; 95% CI: 2.75-13.78), spontaneous labor (38%; RR: 2.80, 95%CI: 1.51-5.18), maternal blood transfusion (9%; RR: 7.18; 95%CI: 0.90-57.01), and preterm delivery before 34 weeks (46%; RR: 9.2; 95%CI: 3.81-22.19). The reason for the increased incidence of these complications is related to the nature of the open fetal procedure, which involves a multi-faceted invasive approach including maternal laparotomy, large hysterotomy with uterine edge stapling, and open fetal repair of the spina bifida defect that may involve manipulation and exposure of the fetus for a significant amount of time.

Fetal endoscopic surgery has progressed rapidly over the past decades and the investigators are now able to perform a number of intricate procedures inside the uterus with specially designed instruments. These procedures include laser therapy for Twin-twin-transfusion syndrome, fetal cystoscopy and fulguration of posterior urethral valves, release of amniotic bands, and placement of various shunts and balloons inside fetal structures and cavities (peritoneal, pleural, cardiac, and trachea).

Fetoscopy offers a less invasive therapeutic option that could reduce a number of the morbidities (both maternal and fetal) related to open fetal procedures.

A few animal studies and some clinical human experience with fetoscopic repair of MMC have been reported showing the feasibility of covering the defect with a patch and sealant, or even in performing a full repair. These repairs have been accomplished using at least two (and sometimes more) entry ports through the uterine wall. Kohl et al. in Germany, have demonstrated the feasibility of performing a complete percutaneous fetoscopic repair of MMC using carbon dioxide to distend the uterus and provide a dry working area for the surgeon to perform the repair.

These investigators described a two-layer covering technique using an absorbable patch (Durasis, Cook, Germany) and sutures. However, while they showed that the procedure is feasible, their percutaneous technique with complete two layer surgical closure of the defect using sutures was associated with prolonged operative time and significant maternal and obstetrical morbidities.

Fetoscopy in a CO2 gas filled uterus has been recently reported by groups in Bonn, Germany (Kohl et al) and Sao Paulo, Brazil (Pedreira et al). The fetoscopic technique the investigators use has been developed and tested in a fetal sheep model of MMC by the investigators group and others (Peiro et al).

This fetoscopy technique has evolved over time to a 2-port technique developed by our team in Houston, Texas and its feasibility and applicability to the human uterus and fetus have been demonstrated and published (Belfort et al, 2017) and demonstrate an improved degree of flexibility in terms of access to the fetus regardless of placental location. The technique is designed to decrease the maternal risks of open uterus fetal surgery while maintaining a similar level of fetal benefit as seen in the MOMS trial.

The investigators technique employs an open abdomen/exteriorized (but closed) uterus methodology that allows the minimally invasive multi-layer closure of the fetal neural tube using the same closed skin repair currently employed at Baylor College of Medicine/Texas Children's Fetal Center using the open uterus approach. The technique employs a novel approach to low pressure uterine distention using the same carbon dioxide gas 8-12 mmHg that others attempting fetoscopic repair have used, but employing a much lower gas flow rate and pressure. In addition, our technique (as compared with the percutaneous method) allows improved access to the fetus in anterior placentation, ability to manipulate and maintain the fetus in the required position, and optimal port placement resulting from the exteriorized maternal uterus.

In addition, because of the exteriorized uterus and the optimal placement this allows, we require only two access ports and these can be sutured into the uterus allowing a closed seal and minimizing gas leakage. The use of humidified, warmed CO2, which we pioneered in fetal surgery, decreases membrane disruption and may prolong gestation without rupture of the membranes. Finally, recent advances in miniature surgical instruments (Storz 1.5 - 3mm surgical sets) allow unprecedented flexibility which enables a full surgical repair to be performed via a fetoscopic approach.

In preparation for the human trial we were able to perform, in a sheep model, dual access port fetoscopic neural tube closure using a 12 F cannula, a second 9F cannula, a cover patch, and a medical sealant with similar results to that seen with open fetal surgical repair in the same sheep model.26

We have now completed almost 50 cases using our 2 port exteriorized technique with results that are reflect our initial hypothesis (Belfort et al , 2017). As with any technique there have been advances in instrumentation and technique and the study is ongoing investigating the multilayer closure technique.

In this protocol, the repair of the open neural tube defect will follow the same principles as we use in open repairs currently being done at this institution. This involves release of the placode, dissection of the surrounding skin and attempted primary closure of the defect using a Durepair patch, a muscle or duro-fascial flap, and available skin. In those cases where we are able to complete the procedure with full skin closure of the defect, the only difference between the open uterus procedure and the fetoscopic procedure, will be that the surgery will be done fetoscopically rather than through an open uterine incision. If we are unable to close the skin primarily despite best fetoscopic efforts, the option of performing/completing the repair as an open procedure exists and will be offered to the patient. The patient is monitored in hospital until ready for discharge.

Approximately 6 weeks after the surgery a post-procedure fetal MRI will be performed. If there is evidence of good closure of the neural tube defect and reversal of the Chiari II malformation, a vaginal delivery can be attempted based on obstetric criteria. Patients will be followed in person every 3-4 months after birth to 12 months at the Spina Bifida Clinic at TCH. Remaining visits will be yearly up to 5 years. If this is not possible, questionnaire(s) will be mailed to the child's parents and records will be requested from the treating neurosurgeon on this same schedule.