Myelomeningocele (MMC) is the most severe form of spina bifida, a group of birth defects that affect the spine and spinal cord. In MMC, the spinal cord and meninges (the protective coverings around the spinal cord) protrude through an opening in the backbone, most often in the lower back. Because delicate nerve tissue is exposed, myelomeningocele can lead to lifelong challenges with movement, bladder and bowel function, and overall development. 

Although MMC is present at birth, early diagnosis, timely surgery, and coordinated long-term care can make a meaningful difference in outcomes. Public health measures, especially folic acid before and during early pregnancy, have lowered rates in many regions, but MMC continues to occur and remains a major cause of disability around the world. This article explains what MMC is, how and why it develops, how it is detected, and how it is treated throughout infancy, childhood, and adulthood. 

Myelomeningocele is an open neural tube defect in which the meninges, spinal cord, and nerve roots herniate through a defect in the vertebral arches. The lesion is typically visible at birth as a fluid-filled sac in the lumbosacral area, and in many cases the sac is covered only by a thin membrane or is open, exposing neural tissue. 

Spina bifida encompasses a spectrum: 

• Spina bifida occulta: A hidden bony defect without protrusion of meninges or spinal cord. 

• Meningocele: Herniation of the meninges through the vertebral defect without spinal cord involvement. 

• Myelomeningocele: Herniation of both meninges and spinal cord, with exposed neural elements and highest risk of neurological impairment. 

MMC is the most clinically significant type because it directly involves nerve tissue, leading to motor, sensory, orthopedic, and urological complications. 

During early pregnancy, the neural tube forms and closes to become the brain and spinal cord. This process, called neurulation, should be complete by about day 28 of gestation—often before many people know they are pregnant. Myelomeningocele occurs when the posterior (back) portion of the neural tube fails to close completely. The resulting spinal defect allows the spinal cord and meninges to protrude, and the exposed neural tissue is vulnerable to injury in the womb. 

Two concepts help explain how damage occurs: 

• Primary neurulation failure: The initial “first hit” is the failure of neural tube closure in the 4th week of gestation. 

• Two-hit hypothesis: After the failure of closure, a “second hit” occurs—ongoing chemical and mechanical injury from amniotic fluid and fetal movement further damages exposed nerve tissue. 

The defect most often occurs in the lumbosacral region (for example, around L5–S1), but it can appear anywhere along the spine. Neurologic deficits reflect the level of the lesion and may be compounded by associated anomalies such as Chiari II malformation, where parts of the lower brain herniate downward and can obstruct cerebrospinal fluid (CSF) flow, causing hydrocephalus. 

Risk Factors

Myelomeningocele arises from a mix of genetic susceptibility and environmental influences during very early pregnancy. While no single cause explains every case, several modifiable and non‑modifiable risk factors have been identified. 

Maternal factors 

• Folic acid deficiency (major modifiable risk factor) 

• Pre‑existing diabetes 

• Obesity 

• Hyperthermia in early pregnancy (for example, sauna use, high fevers) 

• Use of certain medications (such as valproic acid or carbamazepine) 

• Low socioeconomic status and limited access to prenatal care 

Genetic factors 

• Family history of neural tube defects (NTDs) increases recurrence risk 

• Multifactorial inheritance; variants in folate metabolism genes (e.g., MTHFR) and other pathways have been implicated 

Environmental factors 

• Exposure to teratogens (certain drugs, alcohol) 

• Poor overall nutritional status 

Understanding how common MMC is— and who is most affected—helps guide prevention and care: 

• Prevalence: Approximately 0.5–1 per 1,000 live births in the United States; higher rates in some regions with limited folic acid fortification. 

• Sex: Slight female predominance has been reported. 

• Trends: Incidence has declined where folic acid supplementation and food fortification programs are in place, but MMC remains a significant cause of morbidity globally. 

Clinical features depend on the lesion’s level and severity, as well as any associated brain and spine abnormalities. Findings are usually apparent at birth but evolve over time. 

Neurologic findings 

• Flaccid paralysis or weakness below the level of the lesion 

• Loss of sensation below the lesion 

• Neurogenic bladder and bowel (urinary retention or incontinence, constipation) 

• Hydrocephalus in 80–90% of infants due to Chiari II malformation 

Orthopedic manifestations 

• Clubfoot (talipes equinovarus) 

• Hip dislocation or dysplasia 

• Scoliosis and kyphosis 

• Joint contractures and lower-extremity deformities 

Cutaneous findings 

• Visible sac-like protrusion in the lumbosacral area, often covered by a thin membrane 

• Occasionally ruptured at birth with exposed neural tissue 

Associated anomalies 

• Chiari II malformation 

• Tethered cord (progressive neurologic decline with growth) 

• Cognitive and learning challenges 

• Latex allergy (common after repeated healthcare exposures) 

Prenatal diagnosis 

Early detection allows for counseling, planning delivery at a specialized center, and considering fetal surgery in appropriate cases. 

• Maternal serum alpha‑fetoprotein (MSAFP): Elevated levels at 16–18 weeks can suggest an open NTD. 

• Ultrasound (2nd trimester): Shows spinal defect and classic cranial signs—lemon sign (frontal bone scalloping) and banana sign (cerebellar herniation). A cystic mass over the spine may be seen. 

• Amniocentesis: Elevated AFP and acetylcholinesterase in amniotic fluid support the diagnosis when needed. 

Postnatal diagnosis 

• Physical exam: Visible sac, neurologic deficits, and level of involvement. 

• Neuroimaging: MRI or CT of spine to define anatomy and associated anomalies; cranial ultrasound to screen for hydrocephalus and Chiari II. 

Differential Diagnosis 

Conditions that may mimic or overlap with MMC include: 

• Meningocele (meningeal sac without spinal cord in the defect) 

• Lipomyelomeningocele 

• Sacrococcygeal teratoma 

• Dermal sinus tract 

Careful imaging and examination distinguish these entities and guide treatment. 

Optimal care begins before birth (when possible) and continues throughout life. Management typically involves neurosurgery, urology, orthopedics, rehabilitation, and developmental pediatrics, coordinated through a spina bifida clinic or similar multidisciplinary program. 

Prenatal management 

Counseling 

• Discuss prognosis, potential disabilities, options for fetal or postnatal repair, and likely need for long-term therapies. 

Fetal surgery (in utero repair) 

• The MOMS trial showed that repairing MMC before 26 weeks can reduce the need for shunt placement for hydrocephalus and improve lower-limb motor outcomes. 

• Benefits: Lower shunt rates, improved motor function, less hindbrain herniation. 

• Risks: Preterm birth, maternal morbidity (uterine scar, transfusion risk), and the need for delivery by cesarean in current and future pregnancies. 

Immediate postnatal care 

• Protect the sac from drying and infection; cover with sterile, moist, non‑adherent dressings. 

• Position the infant prone to avoid pressure on the lesion. 

• Begin prophylactic antibiotics per institutional protocol. 

• Assess for hydrocephalus and associated anomalies. 

Surgical repair 

• Timing: Typically within 24–48 hours of birth to reduce infection risk and prevent further neural injury. 

• Goal: Close the defect and reconstruct soft tissue coverage; repair does not restore lost neurologic function but helps prevent additional damage. 

Hydrocephalus management 

• Close monitoring of head circumference and fontanelles. 

• Ventriculoperitoneal (VP) shunt placement when indicated (a small tube that drains excess brain fluid into the belly to relieve pressure) or endoscopic third ventriculostomy (ETV) in some centers (a camera‑guided procedure that creates a new pathway for fluid to flow). 

Multidisciplinary long‑term care 

Neurosurgery 

• Monitor for shunt malfunction or infection. 

• Evaluate and treat tethered cord and Chiari II–related issues. 

Urology 

• Manage neurogenic bladder with clean intermittent catheterization (CIC) and anticholinergics. 

• Regular renal ultrasounds and urodynamics to protect kidney function and prevent hydronephrosis. 

Orthopedics 

• Correct deformities (for example, clubfoot), monitor scoliosis, provide bracing. 

• Plan mobility aids (walkers, crutches, wheelchairs) tailored to level of function. 

Rehabilitation and therapy 

• Physical therapy to optimize strength and mobility. 

• Occupational therapy for self‑care and adaptive strategies. 

Developmental, psychosocial, and educational support 

• Neuropsychological evaluation and individualized education plans (IEPs) when needed. 

• Family counseling, social work support, and transition planning for adolescence and adulthood. 

Neurologic 

• Hydrocephalus and shunt complications 

• Tethered cord syndrome with progressive weakness or orthopedic decline 

• Chiari II–related breathing or swallowing problems in severe cases 

Urologic 

• Recurrent urinary tract infections 

• Vesicoureteral reflux and renal scarring 

• Chronic kidney disease from high bladder pressures if untreated 

Orthopedic 

• Progressive scoliosis and kyphosis 

• Hip dislocation, foot deformities, fractures from reduced bone density 

Other 

• Latex allergy (common in spina bifida; latex‑free precautions are recommended) 

• Pressure ulcers due to decreased sensation and mobility 

• Cognitive and learning difficulties, especially with hydrocephalus 

Folic acid is the most effective preventive measure for neural tube defects: 

• General recommendation: 400 mcg folic acid daily starting at least one month before conception and continuing through the first trimester. 

• High‑risk individuals: 4 mg daily (for those with prior NTD‑affected pregnancy or on certain anti‑seizure medications), under clinician guidance. 

Additional measures include: 

• Optimizing diabetes control before conception 

• Reviewing medications with a healthcare professional before pregnancy 

• Achieving a healthy pre‑pregnancy weight 

• Public health strategies such as folic acid food fortification and community education 

Outcomes vary widely and depend on lesion level, timing and quality of surgical care, presence of hydrocephalus, and access to comprehensive follow‑up. Many children with lesions at or below L3 can achieve household or community ambulation with assistive devices. Cognitive outcomes range from typical to impaired; hydrocephalus raises the risk of learning difficulties. With coordinated care, many individuals attend school, work, and live independently, though ongoing support for bladder, bowel, and mobility issues is often necessary. 

Myelomeningocele is a complex condition that begins before birth and affects multiple body systems throughout life. Early recognition through prenatal screening, timely surgical repair, and careful management of hydrocephalus are central to improving outcomes. Equally important are long‑term, team‑based strategies that protect kidney function, support mobility, and foster learning and independence. Prevention through adequate folic acid remains the cornerstone of public health efforts to reduce MMC worldwide. 

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