Spina bifida is a congenital spinal malformation belonging to the spectrum of neural tube defects (NTDs), arising from incomplete closure of the neural tube during early embryogenesis. Occurring during gestational days 21–28, clinical severity spans asymptomatic bony arch defects to severe neural exposure requiring fetal or early postnatal neurosurgical repair.
Neural tube closure normally occurs between the third and fourth weeks of gestation (approximately days 21–28). Disruption of this process results in defective fusion of the vertebral arches and varying degrees of involvement of the spinal cord and surrounding structures. The clinical presentation ranges from asymptomatic bony defects to severe forms characterized by exposure of neural elements and significant neurological impairment. Disease severity is primarily determined by the type and anatomical level of the defect, frequently evaluated alongside associated dysraphic conditions like tethered spinal cord syndrome and diastematomyelia.
Types of Spina Bifida
Spina bifida is broadly categorized into three principal anatomical forms:
Spina Bifida Occulta
This is the mildest and most common form, characterized by a small vertebral arch defect without herniation of neural tissue. The spinal cord remains in its normal anatomical position, and most individuals are asymptomatic. Occasional cutaneous markers like a dermal dimple, localized hypertrichosis (hairy patch), or nevus may be present.
Meningocele
In meningocele, the meninges protrude through the vertebral defect, forming a cystic sac filled with cerebrospinal fluid (CSF). The spinal cord remains intact inside the spinal canal. Neurological deficits are usually absent or mild, and surgical repair yields highly favorable outcomes.
Myelomeningocele
This represents the most severe form. Both the meninges and spinal cord herniate through the vertebral defect into an open sac. Patients exhibit motor paralysis, sensory loss, neurogenic bladder/bowel dysfunction, and a strong co-occurrence with pediatric hydrocephalus and Arnold–Chiari malformation type II.
Symptoms of Spina Bifida
Clinical manifestations vary significantly based on the anatomical level (cervical, thoracic, lumbar, or sacral) and extent of the spinal lesion:
- Weakness, flaccid paresis, or paralysis of the lower extremities
- Sensory deficits (loss of pain, touch, or temperature) below the lesion level
- Impaired or absent ambulation mechanics
- Urinary and fecal incontinence secondary to neurogenic sphincter dysfunction
- Orthopedic deformities (e.g., clubfoot/pes equinovarus, hip dislocation, scoliosis, or kyphosis)
- Visible lumbosacral fluid-filled mass or open spinal placode lesion
- Signs of raised intracranial pressure and progressive macrocephaly from hydrocephalus
Causes and Risk Factors
The etiology of spina bifida is multifactorial, involving an interplay of genetic susceptibility, maternal metabolic factors, and environmental exposures during early organogenesis:
Nutritional & Metabolic Factors
- Periconceptional Folate Deficiency: The single most significant modifiable risk factor.
- Maternal Metabolic Diseases: Pre-gestational diabetes mellitus and maternal obesity.
- Maternal Hyperthermia: High fever or saunas during gestational weeks 3–4.
Genetic & Environmental Factors
- Genetic predisposition and positive family history of neural tube defects
- In utero exposure to teratogenic antiepileptic drugs (particularly valproic acid)
- Inadequate access to early prenatal medical care
Periconceptional folic acid supplementation (400 mcg to 4 mg daily) significantly reduces the baseline incidence of open neural tube defects worldwide.
Diagnosis of Spina Bifida
1. Prenatal Screening & Diagnosis
Advances in fetal medicine enable precise intrauterine detection and risk stratification:
Maternal Serum Alpha-Fetoprotein (MSAFP)
Measured between 15 and 20 weeks of gestation. Elevated MSAFP levels suggest an open neural tube defect allowing fetal protein leakage into maternal circulation, warranting targeted ultrasound confirmation.
Detailed Prenatal Ultrasonography
The primary diagnostic screening modality. Direct findings include widened spinal canal ossification centers and cystic protrusions. Indirect cranial signs include the frontal bone scalloping ("lemon sign") and cerebellar displacement ("banana sign").
Fetal MRI & Amniocentesis
Fetal MRI provides soft-tissue anatomical resolution of the neural placode and brainstem to guide fetal surgery. Amniocentesis confirming elevated amniotic fluid AFP and acetylcholinesterase (AChE) is definitive for open defects.
2. Postnatal Evaluation
Although open lesions are obvious at birth, thorough multi-system evaluation characterizes functional impairment:
- Physical & Neurological Exam: Assessment of motor strength, sensory dermatomes, deep tendon reflexes, and spinal defect integrity.
- Spinal & Cranial MRI: Comprehensive visualization of the spinal cord, low-lying conus, tethered cord, associated lipomas, split cord malformations, and ventricular size.
- CT Scans & Urodynamic Testing: Thin-slice CT evaluates complex vertebral arch defects, while urodynamics evaluates detrusor sphincter dyssynergia and bladder compliance.
Treatment of Spina Bifida
Management requires a coordinated, multidisciplinary team providing surgical repair, shunt placement, and long-term functional rehabilitation:
1. Prenatal (Fetal) Surgery
Performed in selected myelomeningocele cases between 19 and 26 weeks of gestation (MOMS trial criteria).
- Objectives: Protect neural placode from amniotic fluid neurotoxicity and halt secondary hindbrain herniation.
- Benefits: Markedly reduces hydrocephalus shunting rates and improves independent walking ability.
- Risks: Preterm labor, chorioamnionitis, uterine scar dehiscence, and maternal surgical risks.
2. Postnatal Neurosurgical Repair
Standard care for infants not undergoing fetal repair, performed within 24 to 48 hours after birth.
- Reconstructs the dural sac and closes the spinal defect
- Prevents ascending central nervous system infections (meningitis)
- Preserves residual neurological function and prevents fluid leaks
3. Management of Hydrocephalus & Tethered Cord
Secondary hydrocephalus is managed using ventriculoperitoneal (VP) shunts or Endoscopic Third Ventriculostomy (ETV). Children are monitored for late tethered cord syndrome, performing surgical detethering if progressive leg weakness, pain, or bladder dysfunction occurs.
Outlook and Long-Term Care
Spina bifida is a lifelong complex disorder managed effectively through coordinated, multi-specialty care. Lifelong surveillance involving pediatric neurosurgery, perinatology, urology (clean intermittent catheterization), orthopedics (bracing and deformity correction), and physical rehabilitation maximizes mobility, protects renal function, and supports long-term independence and quality of life.
Frequently Asked Questions
What are the three main types of spina bifida?
The three principal forms are spina bifida occulta (the mildest and most common), meningocele, and myelomeningocele (the most severe). They differ in whether the meninges and spinal cord herniate through the vertebral defect and in the degree of neurological involvement.
What causes spina bifida?
The cause is multifactorial, involving both genetic and environmental factors. Recognized risk factors include folate deficiency, genetic predisposition, maternal diabetes or obesity, certain antiepileptic drugs such as valproate, maternal hyperthermia in early pregnancy, and inadequate prenatal care.
Can spina bifida be detected before birth?
Yes. Prenatal detection may involve maternal serum alpha-fetoprotein (MSAFP) screening, second-trimester ultrasonography (including the "lemon" and "banana" signs), fetal MRI when ultrasound is inconclusive, and amniocentesis measuring AFP and acetylcholinesterase.
Can spina bifida be treated with surgery before birth?
In selected cases of myelomeningocele, prenatal (fetal) surgery may be performed to protect exposed neural tissue. Reported benefits include a lower need for ventriculoperitoneal shunting and improved motor outcomes, while potential risks include preterm delivery and maternal complications.
Is spina bifida a neural tube defect?
Yes. Spina bifida belongs to the spectrum of neural tube defects and results from incomplete closure of the neural tube during early embryonic development.
Can spina bifida be prevented?
Periconceptional folic acid supplementation has been shown to significantly reduce the incidence of neural tube defects, making folate status the most significant modifiable factor.