Fetal spina bifida surgery to repair myelomeningocele is a remarkable and intricate procedure performed before birth. If untreated, spinal cord damage from amniotic fluid exposure is progressive during gestation. Highly skilled surgeons close a gap in the fetus’ spine that allows a portion of the spinal cord and nerves to protrude precariously. In each complex case, clinicians from the Center for Fetal Diagnosis and Treatment at The Children’s Hospital of Philadelphia and expectant families must weigh the potential benefits of fetal surgery with the risks, which include preterm birth.
A major reason for performing fetal spina bifida surgery is to avoid placing a shunt later on to avoid a life-threatening buildup of cerebrospinal fluid (CSF) and pressure in the brain called hydrocephalus. If untreated, hydrocephalus can cause irreversible brain damage.
A research article published in the Journal of Neurosurgery: Pediatrics and co-authored by CHOP investigators reported on updated data from the 2011 Management of Myelomeningocele Study (MOMS), a landmark trial that showed corrective spinal surgery in the womb led to decreased rates of shunting at 12 months and was associated with higher scores on tests of mental development and motor function at 30 months. CHOP was one of three fetal surgery programs that participated in the original MOMS trial.
The current analysis took a closer look at magnetic resonance imaging (MRI) scans of the fetuses’ ventricles, the fluid-filled cavities inside their brains, which were performed in both the prenatal (91 women) and postnatal (92 women) surgery groups as part of the MOMS trial. The researchers found that larger ventricles at initial screening are associated with an increased risk for shunting in both groups.
In the prenatal surgery group, 20 percent of those with ventricle size smaller than 10 mm, 45.2 percent with ventricle size of 10 mm up to 15 mm, and 79.0 percent with ventricle size bigger than 15 mm eventually received a shunt; whereas, in the postnatal group, 79.4 percent, 86.0 percent, and 87.5 percent, respectively, required a shunt.
“During prenatal counseling, care should be exercised in recommending prenatal surgery when the ventricles are 15 mm or larger because prenatal surgery does not appear to decrease the shunt rate in this group,” the authors concluded. They determined that the ideal candidate for in utero intervention is a fetus with ventricles smaller than 10 mm. For cases with ventricles 15 mm or greater, they suggested a cautious approach during prenatal counseling when predicting the need for shunting.
These findings also have theoretical implications for the timing of prenatal surgery, the authors pointed out, because fetuses younger than 20 weeks have even tinier ventricles. Ventricles in a fetus with spina bifida tend to enlarge during gestation.
”These findings impact the counseling of families when the fetus already has very large ventricles of 15 mm or larger,” said N. Scott Adzick, MD, Surgeon-in-Chief of The Children's Hospital of Philadelphia and the founder and director of the Center for Fetal Diagnosis and Treatment. “All of the pros and cons of fetal surgery are discussed with these families, keeping in mind the other benefits of fetal surgery including possible improved leg function and better prospects for walking. Our research in Dr. Alan Flake’s laboratory at CHOP is focused on using tissue engineering approaches for prenatal closure of myelomeningocele combined with minimally invasive fetoscopic approaches to treat the spina bifida fetus earlier in gestation (less than 20 weeks gestation). Tissue engineering would seal the myelomeningocele defect, prevent exposure of the developing spinal cord to the ravaging neurotoxic effects of amniotic fluid, and stop CSF leakage from the defect, thereby averting the development of hydrocephalus and the need for a shunt after birth.”
As the most common central nervous system birth defect, spina bifida affects approximately 1,500 babies born in the U.S. each year, and myelomeningocele is the most serious form. The Center for Fetal Diagnosis and Treatment has performed more 244 fetal surgeries on babies with myelomeningocele. PBS Television recently presented a documentary series about the carefully coordinated care that the Center offers families.
The current study’s first author is Noel B. Tulipan, MD, of Vanderbilt University, Nashville. Dr. Adzick is the senior author. The other co-authors are from George Washington University, Washington, D.C.; University of California, San Francisco; Columbia University, New York; and the Eunice Kennedy Shriver National Institute of Child Health and Human Development, Bethesda, Md.