Myelomeningocele, Prenatal (Fetal) Repair



Myelomeningocele, Prenatal (Fetal) Repair


Gregory G. Heuer

N. Scott Adzick





ANATOMY



  • The MMC results from failure of neurulation resulting in an “open book” of distinct elements that are normally closed over the spinal cord (FIG 1) as described in the Myelomeningocele, Postnatal Closure chapter.


PATHOGENESIS



  • During neurulation, normally the neural tube undergoes an ordered process of formation and closure as described in the Myelomeningocele, Postnatal Closure chapter.


NATURAL HISTORY



  • MMC leads to irreversible loss of nerve function at the level of the exposed spinal cord as described in the previous chapter (Myelomeningocele, Postnatal Closure).


  • In addition, a fetus with MMC will progressively develop two associated conditions as the result of the continued cerebrospinal fluid (CSF) leak, a Chiari malformation with hindbrain herniation and hydrocephalus.2






FIG 1 • Appearance of an exposed MMC defect during a fetal repair. The neural placode (pl) is seen at the center. This is surrounded by the zona epitheliosa (ze) and the skin (sk). The myofascial layer (mf) covered by dura can be seen through the translucent arachnoid.


PRENATAL EVALUATION



  • Expectant mothers receive extensive prenatal testing to determine if they are candidates for prenatal surgery. The inclusion and exclusion criteria in the MOMS trial are still used by most fetal therapy centers (Table 1).3


  • Ultrasound (US) examination is performed for three reasons: to define the MMC defect and its spinal level, look at associated CNS abnormalities, and evaluate the fetus for other structural abnormalities.


  • With regard to the MMC defect and CNS-associated conditions, US is used specifically:



    • To define the level of bone and skin opening


    • To analyze the posterior fossa, specifically to look for the presence of hindbrain herniation (must be present as it confirms an open neural tube defect)


    • To determine the size of the lateral ventricles and degree of ventriculomegaly


    • To look for any associated abnormalities such as a spinal cord syrinx, a split cord malformation, or a significant kyphosis that may affect the eligibility of the patient for fetal MMC repair.


  • Patients also receive a fetal magnetic resonance imaging (MRI) scan. These scans provide a more detailed anatomic evaluation of the MMC defect and associated abnormalities, particularly the presence of hindbrain herniation.


  • In addition to imaging, the fetus undergoes an analysis for genetic or chromosomal abnormalities. Also, amniotic fluid analysis is performed to confirm an open neural tube defect.


  • A detailed medical history for the mother is obtained, specifically looking for significant maternal health issues and risk factors associated with premature delivery.


SURGICAL MANAGEMENT



  • The overall goal of the surgical repair is to obtain a multilayer closure that is watertight. To provide the greatest possible benefit to the fetus, the closure needs to protect the neural structures from direct trauma, prevent the leakage of CSF, and prevent the exposure of the neural structures to amniotic fluid. Additionally, the closure needs to be done in a manner that is safe for the fetus and the mother, as extreme premature birth can erase all potential gains of the surgical procedure. There are some modifications of the general technique outlined below, but the principles above should not be compromised.


Preoperative Planning3

Feb 27, 2020 | Posted by in Pediatric plastic surgery | Comments Off on Myelomeningocele, Prenatal (Fetal) Repair
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