What Is Myelomeningocele?
Myelomeningocele is a severe form of neural tube defect in which both the spinal cord and meninges herniate through an opening in the vertebral column. The exposed neural tissue lies within a membranous sac or, in some cases, remains uncovered at birth. It represents the most complex and disabling variant of spina bifida cystica and is associated with lifelong neurological, orthopedic, and urological complications.
Under normal embryologic development, the neural tube completes its closure by the end of the 4th gestational week. When this developmental sequence fails, the posterior vertebral arches do not form correctly, leaving the spinal cord unprotected and allowing neural tissue to protrude. Because functioning spinal nerve roots extend into the sac, myelomeningocele carries a far more significant neurological burden than meningocele.
Embryology and Pathophysiology
Myelomeningocele arises from a failure of primary neurulation, coupled with a defect in vertebral bone formation. As a result, the meninges, cerebrospinal fluid, and neural elements herniate through a posterior spinal defect.
Typical sac contents include:
Meninges
Cerebrospinal fluid
Spinal cord tissue
Nerve roots
The exposed neural tissue undergoes damage in utero and continues to deteriorate after birth if left untreated. Nearly all cases are associated with Chiari II malformation, in which hindbrain structures descend into the cervical spinal canal, contributing to hydrocephalus and brainstem dysfunction.
Common Locations
Myelomeningocele most frequently affects the:
Lumbosacral region (most common)
Thoracolumbar spine
Less commonly, cervical or thoracic levels
Neurological severity increases when the defect is located at higher vertebral levels, since more nerve tissue is involved.
Etiology and Risk Factors
Myelomeningocele results from a multifactorial interplay of genetic predisposition, nutritional deficiency, and maternal health factors. Documented contributors include:
Inadequate periconceptional folic acid intake
Maternal diabetes
Maternal obesity
Hyperthermia in early pregnancy
Antiepileptic drug exposure (e.g., valproate)
Positive family history of neural tube defects
Folic acid supplementation before conception and in early pregnancy has dramatically reduced the incidence of myelomeningocele worldwide.
Clinical Features and Presentation
The presentation is generally obvious at birth.
Local Findings
Open spinal defect or fluid-filled sac
Fragile skin or absent skin coverage
Cerebrospinal fluid leakage
Neurological Outcomes
Depending on the level of the lesion, patients may experience:
Lower limb weakness or paralysis
Sensory loss
Bladder and bowel dysfunction
Orthopedic deformities (clubfoot, kyphosis, scoliosis)
Reduced mobility
Associated Conditions
Myelomeningocele is strongly linked to:
Hydrocephalus (common; often requiring shunt placement)
Chiari II malformation
Tethered cord syndrome
Cognitive and learning difficulties in some cases
Prenatal Diagnosis
Most cases can be detected during pregnancy through:
Ultrasound
Visualization of spinal defect
Associated cranial signs (lemon sign, banana sign)
Fetal MRI
Provides detailed assessment of neural structures
Supports surgical planning
Maternal Serum Alpha-Fetoprotein
Often elevated in pregnancies affected by open neural tube defects.
Early prenatal recognition allows consideration of fetal repair and detailed counseling.
Treatment and Management
Postnatal Surgical Repair
Standard care involves early closure of the defect—ideally within the first 72 hours of life—to:
Cover exposed neural tissue
Prevent infection and CSF leakage
Preserve as much neurological function as possible
Fetal Surgery
Selected cases may undergo prenatal myelomeningocele repair, which has shown benefits in:
Reducing hindbrain herniation
Decreasing the need for postnatal shunting
Improving early motor outcomes
Long-Term Care
Ongoing multidisciplinary follow-up is essential, including:
Neurosurgery
Urology
Orthopedics
Physiotherapy
Developmental pediatrics
Prognosis
Outcome varies with lesion level, timing of treatment, and associated brain abnormalities. Many individuals achieve independence and functional mobility using assistive devices, while others require lifelong support. Bladder and bowel dysfunction are frequent, and orthopedic deformities may need surgical correction.
Despite these challenges, advances in prenatal screening, early surgical repair, and rehabilitation have significantly improved survival and quality of life for individuals with myelomeningocele.