Myelomeningocele

Definition: Myelomeningocele (MMC) is the most severe form of spina bifida cystica. It is an open neural tube defect (NTD) where the spinal cord and nerve roots are exposed through a defect in the vertebral arches and skin. The neural tissue (placode) lies on the surface of the back, surrounded by meninges and CSF.

Epidemiology:

• Incidence: Approximately 1 in 1000 live births (variable by geography and folic acid fortification).
• Prevention: Periconceptional folic acid supplementation (0.4mg daily) reduces risk by 50-70%.
• Prenatal Diagnosis: Elevated maternal serum AFP (MSAFP), detailed ultrasound (Lemon sign, Banana sign).
• Trends: Incidence decreasing due to folic acid fortification and prenatal diagnosis/termination.

Genetics and Recurrence:

• Recurrence Risk: If one child is affected, the recurrence risk is 2-4%. If two children are affected, risk increases to 10%.
• Folic Acid (Recurrence): High-dose folic acid (4mg daily) is recommended for subsequent pregnancies if there is a history of NTD.
• Genetic Syndromes: MMC is usually sporadic, but can be associated with trisomy 18 or Meckel-Gruber syndrome.

Embryology: The neural tube closes between days 21-28 of gestation. Failure of posterior neuropore closure results in MMC. This results in:

1. Exposure of Placode: Direct damage and ongoing leakage of CSF.
2. Loss of Innervation: Motor and sensory loss below the level.
3. Skeletal Deformity: Muscle imbalance drives deformity (hip dislocation, clubfoot, scoliosis).
4. Associated CNS Malformations: Chiari II, hydrocephalus.

Chiari Type II Malformation: Present in almost all patients with MMC. The hindbrain (cerebellum, brainstem) herniates through the foramen magnum. This causes:

• Hydrocephalus: 80-90% require shunting.
• Brainstem Dysfunction: Stridor (vocal cord paralysis), apnea, swallowing difficulty.
• Syringomyelia: Cavity formation within the cord.

Tethered Cord: After initial MMC closure, scar formation tethers the neural placode to the dural repair. During growth, differential traction on the cord causes secondary neurological deterioration. This is often insidious.

The visible back lesion and the pattern of neurological deficit must be distinguished from other dysraphic and neuromuscular conditions, because management and prognosis differ sharply.

Neonatal Assessment:

• Urgent Coverage: The open placode must be surgically covered within 24-48 hours to prevent meningitis.
• Neurological Exam: Document motor level (lowest functioning myotome). Check reflexes. Observe spontaneous movement.
• Head Circumference: Monitor for hydrocephalus (increasing HC, bulging fontanelle, sunsetting eyes).

Orthopedic Assessment:

• Spine: Kyphosis (Gibbus)? Scoliosis?
• Hips: Dislocated (common in L3-L4)? Contractures?
• Feet: Clubfoot? Vertical Talus? Calcaneovalgus?
• Overall Posture: Spinal alignment. Pelvic obliquity.

Neurological Monitoring (Lifelong):

• Tethered Cord Surveillance: Annual neuro exam and urodynamics. MRI if any new symptoms (SPASM).
• Shunt Function: Low threshold for shunt series/CT if any change in cognition, headaches, nausea.

Clinical Imaging Atlas

View larger

View larger

View larger

View larger

View larger

Initial Imaging:

1. MRI Brain: Evaluate Chiari II, hydrocephalus, corpus callosum.
2. MRI Spine: Assess conus level, syrinx, tethering (if suspected later).
3. Hip X-rays: AP Pelvis. Assess hip dysplasia/dislocation.
4. Spine X-rays: Evaluate kyphosis, scoliosis, congenital vertebral anomalies.

Urological Workup:

• Urodynamics: Baseline and annual. Assess detrusor function (hyperreflexic vs areflexic), sphincter function.
• Renal Ultrasound: Annual. Monitor for hydronephrosis/reflux.
• VCUG: As indicated.

Functional Assessment:

• Gait Analysis: For ambulatory patients, to plan orthotic needs.
• FIM (Functional Independence Measure): Overall function.

Latex Allergy:

• Affects 30-70% of MMC patients (depending on definition).
• Sensitization occurs from repeated mucosal exposures (surgeries, catheterizations).
• Prevention: Latex-free environment from birth.
• Signs: Urticaria, Angioedema, Bronchospasm, Anaphylaxis.

• Wound Care: Paramount due to insensate skin. Padding. Frequent skin checks.
• Latex Free: Non-latex catheters, gloves, IV tubing.
• Positioning: Avoid pressure on surgical sites and insensate areas.
• Rehabilitation: Intensive physio for gait training post lower limb surgery.

• Survival: Greater than 80% survive to adulthood with modern care.
• Ambulation: Sacral levels walk independently. Thoracic levels are wheelchair-dependent.
• Cognition: Approximately 80% have normal IQ, though learning disabilities are common.
• Quality of Life: Can be excellent with multidisciplinary support.
• Mortality: Primarily from renal failure and shunt complications.

• Timing and selection for fetal repair: MOMS/MOMS2 established benefit, but eligibility is narrow and maternal/obstetric risk (preterm birth, uterine dehiscence) is real. Fetoscopic techniques aim to reduce maternal morbidity, but comparative long-term neurological data versus open repair remain immature.
• Prophylactic vs symptomatic untethering: Almost all repaired cords are radiologically "tethered". There is no consensus to operate on a radiologically low conus in the absence of clinical or urodynamic deterioration - surveillance, not the MRI appearance alone, drives surgery.
• The dislocated hip: Whether to reduce a unilateral or bilateral dislocation in a mid-lumbar (L3-L4) ambulator is genuinely contested; many units now prioritise a level pelvis and balanced sitting over radiographic reduction.
• Kyphectomy: Effective for severe rigid gibbus interfering with sitting and skin integrity, but carries high rates of wound breakdown, implant failure and blood loss; indications and fixation strategy vary between centres.
• Folic-acid dosing for prevention vs recurrence: 0.4 mg/day for general prevention vs 4-5 mg/day for women with a prior affected pregnancy; the optimal dose and the role of universal fortification in voluntary-supplementation countries remain debated.

Global Epidemiology:

• NTD birth prevalence varies widely with diet, fortification policy and prenatal screening: roughly 0.5-1 per 1000 in fortified, high-income settings, but markedly higher in regions without fortification (parts of South Asia, the Middle East and sub-Saharan Africa report several per 1000).
• Mandatory folic-acid fortification of staple flour (adopted by the USA, Canada, Australia, much of Latin America and a growing number of African and Asian countries) has reduced NTD prevalence by an estimated 30-50% at population level. Many European countries still rely on voluntary supplementation alone, where uptake is incomplete.

Side-by-Side Guidance (where recommendations differ):

Registry & Network Data:

• National spina bifida registries and care networks (e.g. the US National Spina Bifida Patient Registry and European reference networks) track ambulation, renal function, shunt revisions and pressure-sore burden, and have driven standardisation of multidisciplinary follow-up.
• Outcome data consistently show that renal preservation (clean intermittent catheterisation, anticholinergics, surveillance) and shunt vigilance are the principal determinants of long-term survival.

High- vs Limited-Resource Practice Variation:

• High-resource: prenatal diagnosis, option of fetal repair, lifelong multidisciplinary clinics, urodynamics-guided bladder management.
• Limited-resource: later presentation (sometimes with neglected, infected or ruptured sacs), limited shunt access, reliance on clinical rather than urodynamic bladder monitoring, and greater dependence on bracing/positioning over reconstructive surgery. Prevention through fortification has the largest public-health impact in these settings.