Chapter 9.7 — Neural Tube Defects & Myelomeningocele

Neural tube defects arise when the neural tube fails to close in early gestation, and they remain among the most consequential congenital anomalies despite being substantially preventable with folic acid. The spectrum runs from anencephaly (incompatible with life) to spina bifida, whose most serious survivable form — myelomeningocele — exposes spinal cord tissue through a vertebral defect, producing lower-limb paralysis, sensory loss, and neurogenic bladder and bowel, and is almost always accompanied by the Chiari II hindbrain malformation and hydrocephalus. Two developments define modern care: prevention (folic acid fortification and supplementation) and prenatal repair (the MOMS trial), which shifts some of the disease burden by operating before birth. Postnatally, the priorities are protecting the exposed tissue, closing it early, managing hydrocephalus, and organizing lifelong multidisciplinary care.

• Embryology: the neural tube normally closes by ~week 4; failure at the caudal end → spina bifida, at the cranial end → anencephaly/encephalocele.
• Open MMC: the exposed neural placode is damaged by contact with amniotic fluid and trauma throughout gestation (the "two-hit" concept — a primary defect plus secondary in-utero injury), which is the rationale for fetal repair.
• Chiari II → hydrocephalus: CSF dynamics are disrupted; most MMC infants develop hydrocephalus requiring treatment.

Prevention (folic acid):

• 400 mcg/day periconceptionally for all who could become pregnant (food fortification has reduced incidence).
• 4 mg/day for those with a prior affected pregnancy or high risk (e.g., on certain antiepileptics).

Risk factors: folate deficiency, maternal diabetes, antiepileptic drugs (valproate, carbamazepine), maternal obesity, hyperthermia, genetic predisposition, prior affected pregnancy.

• Visible spinal lesion (open sac with neural tissue in MMC; skin-covered in meningocele/occulta).
• Neurologic deficits below the level: motor paralysis, sensory loss, and neurogenic bladder and bowel.
• Hydrocephalus (often evident at birth or developing after closure) — increasing head circumference, bulging fontanelle.
• Chiari II symptoms (in some): stridor, apnea, swallowing difficulty.
• Orthopedic: clubfoot, hip dysplasia.

• Prenatal: elevated maternal serum alpha-fetoprotein (MSAFP), elevated amniotic AFP/acetylcholinesterase; ultrasound (spinal defect; cranial signs — "lemon" sign [frontal scalloping] and "banana" sign [cerebellum], ventriculomegaly); fetal MRI for detail and fetal-surgery candidacy.
• Postnatal: examine and characterize the lesion (open vs skin-covered, level), neurologic exam, head circumference/cranial imaging for hydrocephalus, renal/urologic assessment, and orthopedic evaluation.
• Exclude skin-covered dysraphism (lipomyelomeningocele, etc.) — different management, not fetal-surgery candidates.

• Avoid latex gloves at all times. Place the infant prone immediately after delivery to protect the defect and cord from traumatic injury. Cover the lesion with non-adhesive gauze soaked in sterile Ringer's lactate or saline, then plastic wrap as a barrier against the environment and against fluid loss. Notify neurosurgery. An infant who needs resuscitation and must lie supine should be placed on a doughnut-shaped cushion supporting the defect.
• Amoxicillin 10 mg/kg/day for urinary tract infection prophylaxis.
• Measure the fronto-occipital circumference daily with serial cranial ultrasounds for hydrocephalus — most infants will need a shunt. Once the infant can lie supine, do a urological evaluation including renal ultrasound and VCUG. The evaluation after fetal surgery is the same.
• Incidence and recurrence: myelomeningocele occurs in 0.2–0.4 per 1000 live births in the US, higher in the East and South, and more often in females. Recurrence risk is 1.5–3% after one affected sibling and 5.7–12% after two.
• Fetal repair: the randomized trial showed prenatal surgery before 26 weeks reduced shunting and improved motor and neurocognitive outcomes at 30 months — greatest benefit where the ventricle measured under 10 mm at repair — and was stopped for efficacy. The maternal cost is abruption, membrane rupture and uterine dehiscence; the fetal cost is preterm delivery, RDS and apnoea.
• Outcomes worth stating plainly to families: occipital encephalocele — mortality 40–50%, with only about 15% of survivors normal. Postnatal myelomeningocele repair — mortality 15–30%, 30% with an IQ below 80, and 50% unable to live independently. Fetal repair — coordination and gait deficits persist but at a significantly lower rate, 30% still need maximal assistance with life tasks, and no improvement in bowel or bladder continence has been shown over postnatal repair.

• Head circumference and cranial imaging (hydrocephalus).
• Neurologic and urologic status (renal protection is critical).
• Wound healing/infection after closure.
• Chiari II symptoms (respiratory/swallowing).
• Developmental, orthopedic, and continence follow-up over years.