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Congenital malformations

Spina bifida

Spina bifida is a congenital neural tube defect characterized by incomplete closure of the vertebral column and varying degrees of spinal cord and meningeal involvement. It occurs in approximately 1-2 per 1,000 live births worldwide, with significant geographic variation. The most testable fact is that maternal folic acid supplementation (400-800 mcg daily) before conception and during early pregnancy reduces the risk by up to 70%.

Practice questionsHigh-yield facts
ICD-10Q05 (spina bifida aperta), Q76.0 (spina bifida occulta)
Typical patientNewborn with visible lumbosacral sac or subtle skin findings
Key findingElevated maternal serum alpha-fetoprotein (MSAFP) in pregnancy
First-line treatmentFetal or postnatal surgical repair; multidisciplinary supportive care
9 min readFor medical studentsUpdated 2026-10-14

Definition and epidemiology

Spina bifida is a midline defect of the vertebral column resulting from failure of neural tube closure during the third to fourth week of embryonic development. The condition exists on a spectrum from occult forms to severe open defects.

Classification

Spina bifida occulta is the mildest form, involving only a bony defect in the posterior vertebral arch without herniation of neural tissue. It affects 10-20% of the general population and is often asymptomatic and discovered incidentally on imaging.

Spina bifida aperta (open spina bifida) includes:

  • Meningocele: herniation of meninges and cerebrospinal fluid through the vertebral defect, with an intact spinal cord
  • Myelomeningocele: herniation of meninges, CSF, and spinal cord/nerve roots, the most severe and common form (80% of open cases)

Epidemiology

The worldwide prevalence is approximately 1-2 per 1,000 live births, though rates vary significantly by region. Higher rates are observed in Hispanic populations, certain areas of the United Kingdom, and Egypt. Rates have declined substantially in countries with mandatory folic acid fortification programs. Female infants are affected slightly more often than males. The lumbosacral region is involved in 75-80% of cases.

High-yield for exams
  • Maternal folic acid supplementation (400-800 mcg daily) reduces spina bifida risk by 50-70%.
  • Elevated maternal serum alpha-fetoprotein at 15-20 weeks suggests open neural tube defect.
  • Lemon sign (scalloped frontal bones) and banana sign (abnormal cerebellum) are characteristic ultrasound findings.
  • Chiari II malformation occurs in nearly all myelomeningocele cases and causes hydrocephalus in 80-90%.
  • Neurological deficits correlate with lesion level; sacral lesions have best functional outcomes.
  • Neurogenic bladder requires clean intermittent catheterization to prevent renal failure, the leading cause of adult mortality.
  • Valproic acid and carbamazepine are teratogenic anticonvulsants that significantly increase spina bifida risk.
  • Fetal myelomeningocele repair (before 26 weeks) reduces need for VP shunt and improves motor outcomes but increases preterm birth risk.

Etiology and risk factors

Spina bifida results from a combination of genetic susceptibility and environmental factors that disrupt normal neural tube closure.

Genetic factors

Multiple genes involved in folate metabolism, neural tube closure, and embryonic development contribute to risk. Folate pathway genes (MTHFR, MTRR) are particularly important. The recurrence risk after one affected child is 3-5%, rising to 10% after two affected pregnancies, indicating polygenic inheritance.

Environmental and maternal factors

  • Folate deficiency: the single most important modifiable risk factor
  • Maternal diabetes mellitus: 2-10 fold increased risk, particularly with poor glycemic control
  • Maternal obesity: approximately 2-fold increased risk
  • Hyperthermia: fever or hot tub use in early pregnancy
  • Anticonvulsant medications: valproic acid (1-2% risk) and carbamazepine increase risk significantly
  • Ethnicity: Hispanic and Celtic ancestry associated with higher rates
  • Low socioeconomic status: associated with inadequate nutrition and prenatal care

Protective factors: Periconceptional folic acid supplementation (400-800 mcg daily for low-risk women, 4-5 mg daily for high-risk women) reduces occurrence risk by 50-70% and recurrence risk by approximately 70%.

Pathophysiology

Normal neural tube closure occurs between days 21-28 of gestation, proceeding in a zipper-like fashion from multiple closure sites. Failure of posterior neuropore closure results in spina bifida.

Embryological defect

In spina bifida occulta, only the bony elements (vertebral arches) fail to fuse, leaving neural tissue covered by skin. In open forms, the neural placode remains exposed or covered only by a thin membrane. The exposed neural tissue undergoes secondary injury from amniotic fluid exposure, mechanical trauma, and abnormal CSF dynamics.

Associated anomalies

Chiari II malformation occurs in nearly all patients with myelomeningocele. The cerebellar vermis and brainstem are displaced downward through the foramen magnum, often causing hindbrain dysfunction and obstructive hydrocephalus (80-90% of myelomeningocele cases).

Tethered cord syndrome develops when scar tissue anchors the spinal cord, preventing normal ascent during growth and causing progressive neurological deterioration.

Neurogenic bladder and bowel result from damage to sacral nerve roots controlling sphincter function and sensation.

Folate and neural tube closure

Folate is essential for DNA synthesis, methylation reactions, and cell proliferation. Deficiency impairs rapidly dividing neuroepithelial cells during neural tube formation. Genetic polymorphisms in folate metabolism enzymes reduce the efficiency of folate utilization, increasing dietary requirements.

Clinical features

Clinical presentation varies dramatically based on the type and level of the lesion.

Spina bifida occulta

Most cases are asymptomatic and discovered incidentally. Cutaneous stigmata may be present over the defect:

  • Tuft of hair (faun tail)
  • Dimple or sinus tract
  • Hemangioma or lipoma
  • Hyperpigmented patch

Some patients develop tethered cord syndrome in childhood or adolescence with progressive lower extremity weakness, gait abnormalities, back pain, scoliosis, or urinary dysfunction.

Meningocele

A visible fluid-filled sac is present at birth, usually in the lumbosacral region. The sac transilluminates and contains only CSF and meninges. Neurological function is typically normal or near-normal, though some patients have bladder dysfunction or lower extremity weakness.

Myelomeningocele

The most severe form presents with a visible sac or exposed neural placode at birth. The sac may leak CSF and is at high risk for infection (meningitis).

Neurological deficits correlate with lesion level:

  • Motor: flaccid paralysis below the lesion level, hip dislocation, clubfoot deformities
  • Sensory: absent sensation below the lesion
  • Autonomic: neurogenic bladder (urinary retention, incontinence, recurrent UTIs), bowel incontinence, sexual dysfunction

Associated problems:

  • Hydrocephalus (80-90%): macrocephaly, bulging fontanelle, developmental delay
  • Chiari II malformation symptoms: stridor, apnea, dysphagia, upper extremity weakness
  • Orthopedic: scoliosis, kyphosis, hip dislocation, joint contractures
  • Latex allergy: develops in 20-70% due to repeated exposures
  • Cognitive: learning disabilities in 60-80%, though most have normal intelligence

Prenatal findings

Elevated maternal serum alpha-fetoprotein (MSAFP) at 15-20 weeks gestation. Ultrasound shows absent or abnormal vertebral ossification, lemon sign (scalloped frontal bones), and banana sign (abnormal cerebellar shape).

Diagnosis

Diagnosis is established through prenatal screening and imaging or physical examination at birth.

Prenatal diagnosis

Maternal serum alpha-fetoprotein (MSAFP): elevated at 15-20 weeks in 80-90% of open neural tube defects. AFP leaks from exposed neural tissue into amniotic fluid and maternal circulation. Further evaluation with ultrasound and possibly amniocentesis is warranted.

Ultrasound: second-trimester anatomy scan (18-22 weeks) detects most cases. Findings include:

  • Absence of posterior vertebral elements
  • Splaying of laminae
  • Lemon sign: concave frontal bones
  • Banana sign: abnormal cerebellar curvature (Chiari II malformation)
  • Hydrocephalus
  • Clubfoot or other limb abnormalities

Amniocentesis: elevated amniotic fluid AFP and acetylcholinesterase confirm open neural tube defect when ultrasound findings are equivocal.

Fetal MRI: provides detailed assessment of lesion level, Chiari malformation, hydrocephalus, and associated brain abnormalities.

Postnatal diagnosis

Physical examination: visible sac or exposed placode is diagnostic in open forms. Neurological examination determines motor and sensory levels.

Imaging:

  • Spine radiographs or ultrasound (in neonates): demonstrate bony defect
  • MRI spine and brain: gold standard for detailed anatomy, tethered cord, and Chiari malformation
  • Head ultrasound or CT: assess ventricular size and hydrocephalus

Renal ultrasound: screen for hydronephrosis from neurogenic bladder.

Urodynamic studies: evaluate bladder function and guide management to prevent renal damage.

Differential diagnosis

The differential diagnosis depends on presentation.

For lumbosacral masses in newborns

  • Lipomyelomeningocele: lipoma extending into spinal canal, usually covered by skin
  • Sacrococcygeal teratoma: large, irregular mass extending from sacrum, may be vascular
  • Caudal regression syndrome: associated with maternal diabetes, absent sacral vertebrae
  • Anterior meningocele: rare, pelvic or presacral mass

For skin lesions overlying the spine

  • Dermal sinus tract: can communicate with spinal canal, risk of meningitis
  • Pilonidal cyst or sinus: superficial, does not communicate with spine
  • Lipoma: subcutaneous, not associated with bony defect

For tethered cord symptoms

  • Intraspinal tumor: ependymoma, astrocytoma, lipoma
  • Syringomyelia: fluid-filled cavity within spinal cord
  • Diastematomyelia: split cord malformation
  • Muscular dystrophy or neuropathy: progressive weakness without spinal abnormality

For elevated MSAFP

  • Anencephaly: absent cranial vault
  • Encephalocele: cranial neural tube defect
  • Abdominal wall defects: gastroschisis, omphalocele
  • Multiple gestations
  • Fetal demise
  • Incorrect gestational dating

Management

Management is multidisciplinary, involving neurosurgery, urology, orthopedics, physical medicine, and primary care.

Prenatal management

Fetal surgery (myelomeningocele repair before 26 weeks gestation) improves outcomes in selected cases. The MOMS trial demonstrated reduced need for ventriculoperitoneal shunting and improved motor function at 30 months, though preterm birth and maternal risks are increased. Criteria for fetal surgery include isolated myelomeningocele at T1-S1, Chiari II malformation, and absence of severe kyphosis or other major anomalies.

Cesarean delivery is often recommended for open lesions to reduce trauma and infection risk, though evidence is mixed.

Immediate postnatal care

For myelomeningocele, the exposed sac is covered with sterile saline-soaked gauze. The infant is positioned prone. Prophylactic antibiotics are administered until closure. Early surgical closure (24-72 hours after birth) reduces infection risk and further neurological injury.

Neurosurgical management

Defect closure: primary repair of the meningeal and skin defect, release of tethered cord.

Ventriculoperitoneal shunt: placed for hydrocephalus, required in 80-90% of myelomeningocele patients, often within the first weeks of life.

Chiari II decompression: reserved for symptomatic patients with stridor, apnea, or upper extremity weakness.

Tethered cord release: surgical untethering if progressive neurological deterioration occurs.

Urological management

Goal is preservation of renal function and achievement of continence.

  • Clean intermittent catheterization (CIC): cornerstone of bladder management
  • Anticholinergics (oxybutynin): reduce detrusor overactivity and bladder pressure
  • Bladder augmentation or urinary diversion: for refractory cases
  • Annual monitoring: renal ultrasound, urodynamics, and serum creatinine

Orthopedic management

  • Clubfoot correction: serial casting (Ponseti method) or surgery
  • Hip dislocation management: often left untreated in non-ambulators
  • Scoliosis: bracing or spinal fusion for progressive curves
  • Ankle-foot orthoses (AFOs): support ambulation

Bowel management

  • Bowel regimen: scheduled toileting, dietary modification, stool softeners, stimulant laxatives, or enemas
  • Antegrade continence enema (ACE procedure): surgical option for refractory incontinence

Developmental and rehabilitative care

  • Physical therapy: maximize mobility and prevent contractures
  • Occupational therapy: activities of daily living
  • Special education support: address learning disabilities
  • Psychosocial support: address adjustment, independence, and quality of life

Latex precautions

Latex-free environment for all medical care due to high sensitization risk.

Transition to adult care

Structured transition planning beginning in adolescence addresses independence, sexuality, vocational training, and transfer to adult specialists.

Complications and prognosis

Early complications

  • Meningitis or ventriculitis: from CSF leak or shunt infection
  • Wound dehiscence or CSF leak: after surgical closure
  • Hydrocephalus progression: requiring shunt placement or revision
  • Brainstem dysfunction: from Chiari II malformation (apnea, aspiration)

Long-term complications

  • Shunt malfunction or infection: requires lifelong surveillance, revision rate approximately 40% at 1 year
  • Renal failure: from chronic high-pressure neurogenic bladder, leading cause of mortality in adults
  • Recurrent urinary tract infections: increase risk of renal scarring
  • Tethered cord syndrome: progressive neurological decline requiring surgical release
  • Pressure ulcers: from immobility and insensate skin
  • Obesity: related to immobility
  • Depression and social isolation: more common in adolescents and adults
  • Latex anaphylaxis: can be life-threatening

Prognosis

Survival to adulthood exceeds 90% in developed countries with modern multidisciplinary care. Functional outcomes depend on lesion level:

  • Thoracic lesions: non-ambulatory, wheelchair-dependent
  • High lumbar (L1-L2): limited community ambulation with extensive bracing
  • Low lumbar (L3-L4): community ambulation with AFOs
  • Sacral lesions: independent ambulation, better bowel/bladder control

Most individuals have normal intelligence, though learning disabilities are common. Many achieve independence, employment, and satisfying social relationships with appropriate support. Fetal surgery improves motor outcomes but does not eliminate disability.

Prevention

Folic acid supplementation (400-800 mcg daily) for all women of reproductive age and 4-5 mg daily for women with prior affected pregnancy is the primary prevention strategy. Mandatory fortification of grain products has reduced prevalence by 20-50% in countries with implementation.

Mnemonic

SPINA for key risk factors: Seizure medications (valproate), Poor folate intake, Insulin-dependent diabetes, Nutrition deficiency, Ancestry (Hispanic/Celtic).

Practice questions

1. A 28-year-old woman at 18 weeks gestation undergoes routine prenatal screening. Her maternal serum alpha-fetoprotein (MSAFP) is elevated at 3.5 multiples of the median. Follow-up ultrasound shows splaying of lumbar vertebral arches, bilateral clubfeet, and a banana-shaped cerebellum. Which of the following interventions in a future pregnancy would most effectively reduce recurrence risk?

Answer: C. The ultrasound findings are consistent with myelomeningocele and Chiari II malformation. For women with a prior affected pregnancy, high-dose folic acid (4-5 mg daily) starting before conception reduces recurrence risk by approximately 70%. While glycemic control and avoiding hyperthermia are beneficial, folic acid supplementation has the strongest evidence for prevention. Cesarean delivery and corticosteroids do not reduce recurrence risk.

2. A newborn is delivered with a visible lumbosacral sac covered by a thin membrane. Examination reveals flaccid paralysis of both lower extremities, absent patellar reflexes, and a distended bladder. The head circumference is at the 95th percentile with a tense anterior fontanelle. Which of the following is the most appropriate immediate management?

Answer: B. This infant has myelomeningocele with hydrocephalus. Immediate priorities are to protect the exposed neural tissue from trauma and infection by covering it with sterile saline-soaked gauze and positioning the infant prone. The sac should be surgically closed within 24-72 hours. While the infant likely needs a VP shunt for hydrocephalus, defect closure takes priority. MRI, catheterization, and therapy are important but not the most urgent initial steps.

3. A 10-year-old girl with repaired lumbar myelomeningocele and a ventriculoperitoneal shunt presents with progressive lower extremity weakness, new-onset back pain, and worsening urinary incontinence over the past 6 months. Shunt function is normal. MRI of the spine shows low-lying conus medullaris at the L4 level with a thick filum terminale. Which of the following is the most appropriate next step in management?

Answer: B. This patient has developed tethered cord syndrome, a known complication of spina bifida characterized by progressive neurological deterioration (weakness, pain, worsening bladder function) as the child grows. MRI confirms a low-lying conus and thickened filum. Neurosurgical release of the tethered cord is indicated to prevent further deterioration. While bladder management and therapy are important adjuncts, they do not address the underlying cause. Observation would allow continued neurological decline.

Frequently asked questions

What causes spina bifida?

Spina bifida results from failure of the neural tube to close completely during the third to fourth week of pregnancy, due to a combination of genetic susceptibility and environmental factors. The most important modifiable risk factor is maternal folate deficiency. Other contributing factors include maternal diabetes, obesity, certain anticonvulsant medications (especially valproic acid), hyperthermia in early pregnancy, and genetic variants affecting folate metabolism. Taking folic acid supplements before conception and during early pregnancy reduces the risk by 50-70%.

What are the first symptoms of spina bifida?

In open spina bifida (myelomeningocele), a visible sac or exposed neural tissue on the baby's back is evident at birth, usually in the lower spine region. Associated symptoms include flaccid paralysis of the legs, lack of sensation below the defect, inability to control bladder and bowel function, and clubfoot deformities. In mild spina bifida occulta, there may be no symptoms at all, or only subtle skin changes like a tuft of hair, dimple, or birthmark over the spine. Some children with occult forms later develop progressive weakness, gait problems, or urinary issues as they grow.

How is spina bifida diagnosed?

Spina bifida is most commonly diagnosed prenatally through routine screening. Elevated maternal serum alpha-fetoprotein (MSAFP) at 15-20 weeks gestation prompts further evaluation with detailed ultrasound, which shows the spinal defect and characteristic findings like the lemon sign and banana sign. Fetal MRI provides additional detail. If not detected prenatally, open forms are obvious at birth by physical examination of the visible defect. Occult forms may be discovered later through spine imaging (X-ray, ultrasound in infants, or MRI) when investigating symptoms or incidental findings.

Is spina bifida curable?

Spina bifida is not curable, but it is treatable. Surgical closure of the defect can be performed either before birth (fetal surgery before 26 weeks) or within 24-72 hours after birth to prevent infection and further nerve damage. However, this does not reverse existing neurological damage. Most patients require lifelong multidisciplinary care, including management of hydrocephalus (often with a shunt), neurogenic bladder (catheterization), orthopedic issues, and developmental support. With comprehensive modern care, over 90% of affected individuals survive to adulthood, and many achieve independence and good quality of life, though the degree of disability varies with lesion severity.

Spina bifida vs spinal muscular atrophy — what is the difference?

Spina bifida is a structural birth defect of the spine and spinal cord caused by failure of neural tube closure in early pregnancy, resulting in varying degrees of paralysis, sensory loss, and bladder/bowel dysfunction from birth. In contrast, spinal muscular atrophy (SMA) is a genetic neurodegenerative disorder caused by mutations in the SMN1 gene, leading to progressive loss of motor neurons and muscle weakness that typically appears in infancy or childhood. Spina bifida is preventable with folic acid and involves anatomical malformation visible on imaging, while SMA is inherited, involves normal spinal anatomy, and is diagnosed by genetic testing.

Key drugs

Folic acidOxybutyninTolterodineDocusateBisacodylPolyethylene glycolCephalosporinsBaclofen
Chiari malformationHydrocephalusAnencephalyEncephaloceleTethered cord syndromeNeurogenic bladderClubfoot (talipes equinovarus)Neural tube defects

Sources and further reading

StatPearls (NCBI Bookshelf)MedlinePlusWHO ICD-10: Q76.0

Educational content for medical students, prepared by the WhiteCoat Pro editorial team with AI assistance; every page is reviewed by a second AI model for factual errors. It is not medical advice and does not replace the product label, local guidelines or a clinician.