Fetoscopic Repair of Myelomeningocele (MMC)

Fetoscopic repair of myelomeningocele represents a shift from postnatal correction to intrauterine intervention, and the technical sequence matters as much as the individual steps. This discussion walks through the procedure as performed at a high-volume fetal surgery center, emphasizing the decisions that separate a successful repair from one that fails to achieve watertight closure.

Timing the intervention

Prenatal repair is most commonly done between 22 and 26 weeks gestation 1:44. This window balances fetal size — large enough to tolerate instrumentation, small enough that the uterus accommodates port placement — against the progression of neural injury from ongoing cerebrospinal fluid exposure. Earlier is not necessarily better; the fetus must be developmentally ready for the repair to hold.

Establishing the workspace

The amniotic cavity is expanded using humidified and heated carbon dioxide to create more space for the repair 2:22. This is not optional theatrics — collapsed membranes make instrument manipulation impossible and increase the risk of iatrogenic injury to the fetus. Three ports total are placed: one first port under ultrasound guidance, then two additional ports under direct vision 2:17. The sequence matters because blind placement of multiple ports risks placental laceration or fetal injury. Fetal anesthesia is induced via an intragluteal injection 2:51, and a stabilization stitch is placed in the baby's upper back above the spina bifida 2:56 to prevent movement during dissection.

The untethering step

The placode is freed in a procedure called untethering, which allows it to fall back down into the spinal canal 3:25. This is the mechanically critical moment. The placode — the open area of exposed neural tissue — must be released from its tethered position without injuring the fragile neural elements. If the placode does not fall back freely, the repair will fail to reduce tethering and the neurologic benefit is lost. The sack is opened and dissection is performed circumferentially around it 3:08 to achieve this release.

Achieving watertight closure

Skin flaps are created to loosen the skin and help form a watertight closure of the spinal defect 3:44. The goal is primary skin closure when possible, but the defect size dictates the approach. A patch is placed into the defect to protect the placode and anchored with dissolvable sutures 3:57, followed by a second patch to give additional protection 4:08. The skin is closed over the spinal defect using dissolvable sutures when the baby has enough skin 4:17. If the defect is too big and the skin edges cannot be approximated, a skin patch is used to form a watertight closure 4:26. This is not a failure — it is the correct response to anatomy. Forcing a tension closure risks dehiscence and cerebrospinal fluid leak.

Completing the repair

Removed amniotic fluid is replaced with warm fluid and antibiotics are placed into the amniotic cavity 4:57. Port sites are closed with dissolvable sutures 4:49. The mother and fetus are monitored postoperatively, and if able, the baby is delivered vaginally at term 5:14. The emphasis on vaginal delivery when possible reflects the goal of minimizing maternal morbidity — the mother has undergone a major procedure for fetal benefit, and cesarean section should not be automatic.

The teaching point the discussants returned to repeatedly was the primacy of watertight closure. Every technical step — untethering, flap creation, patch placement, skin approximation — serves that end. A repair that leaves the neural tissue exposed or allows cerebrospinal fluid leak has failed, regardless of how elegant the dissection was.

This discussion walks through the operative steps of fetoscopic myelomeningocele repair, emphasizing the technical choices that determine whether the repair succeeds 1:44 1:54 2:22 2:17. The procedure targets the 22-to-26-week window 1:44, balancing fetal size against the urgency of preventing further spinal cord damage.

Maternal access determines fetal positioning

The choice between transverse and midline abdominal incision 1:54 is not cosmetic. Transverse access tends to position the uterus more favorably for lower lumbar and sacral defects; midline access gives better reach for thoracic lesions 1:54. The incision dictates how much you can rotate the uterus and where your ports will land relative to the fetal spine 1:54.

Amnioinfusion with CO₂ creates the working space

Expanding the amniotic cavity with humidified, heated carbon dioxide 2:22 is what makes fetoscopy feasible here. Cold or dry gas damages the amnion; inadequate insufflation leaves you working in a collapsed space where every instrument movement risks fetal contact 2:22. The gas must be warm enough to avoid hypothermia and humid enough to preserve membrane integrity 2:22. This is not laparoscopy—amniotic fluid dynamics are unforgiving.

Port placement follows a strict sequence

The first port goes in under ultrasound guidance; the next two go in under direct vision once the camera is through 2:17. Placing all three ports blind risks placental laceration or fetal injury 2:17. The camera port position determines your viewing angle for the entire case—if it is too lateral, you lose depth perception on the midline defect 2:17. Once ports are placed, a stabilization stitch in the upper back 2:56 keeps the fetus from rotating during manipulation, which would make the repair impossible 2:56.

Untethering is the step that prevents re-tethering

Opening the sac and dissecting circumferentially 3:08 exposes the placode, but the critical maneuver is freeing it so it falls back into the spinal canal 3:25. Incomplete untethering leaves residual tethering postnatally, negating much of the benefit of fetal repair 3:25. The placode must be mobilized enough to lie without tension inside the canal, but aggressive dissection risks vascular injury to the neural tissue 3:25. This is the step where experience separates adequate from excellent outcomes.

Patch layering protects against CSF leak

A single patch over the placode 3:57 is insufficient. The second patch 4:08 provides redundancy against cerebrospinal fluid leak, which is the most common cause of repair failure 3:57 4:08. Both patches are anchored with absorbable suture, and the suture technique matters—continuous suture risks purse-stringing and patch retraction, while interrupted sutures distribute tension more evenly 3:57 4:08. The patches must cover the defect completely without bunching, which requires accurate sizing before insertion 3:57 4:08.

Skin closure depends on defect size, not preference

When native skin edges can be approximated without tension, primary closure with absorbable suture is preferred 4:17. When the defect is too large, a skin patch is mandatory to achieve watertight closure 4:26. Forcing primary closure on a large defect guarantees dehiscence 4:17 4:26. The skin flaps created earlier 3:44 are what allow tension-free approximation—without adequate undermining, even a moderate defect cannot be closed primarily 3:44 4:17. Watertight closure is non-negotiable; any CSF leak postoperatively risks infection and repair breakdown 4:17 4:26.

Amniotic fluid replacement and antibiotics are the last safeguards

Replacing the amniotic fluid removed during the procedure and instilling antibiotics into the cavity 4:57 reduce the risk of chorioamnionitis, which remains the leading cause of preterm delivery after fetoscopic MMC repair 4:57. The fluid must be warmed to avoid fetal hypothermia 4:57. Port sites are closed with absorbable suture 4:49, and any fascial defect must be closed to prevent herniation during the remainder of the pregnancy 4:49.

The discussants emphasized that vaginal delivery at term remains the goal 5:14, though cesarean section is often required for obstetric indications 5:14. The repair itself does not mandate cesarean delivery, but the risk of preterm labor and membrane complications frequently leads to operative delivery 5:14.