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Spina Bifida

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Overview

Spina bifida (‘split spine’) is a neural tube defect characterised by incomplete closure of the spine and the spinal cord membranes. This can occur anywhere from the base of the skull to the sacrum and is most commonly found in the sacral region.

Neural tube defects

Neural tube defects (NTDs) are a group of disorders describing abnormal fusion of the neural tube. Normal fusion of the neural tube occurs in early pregnancy from day 21 to 28 after conception. NTDs can be classified into:

  • Cranial neural tube defects (such as anencephaly and encephalocele)
  • Spinal neural tube defects (spina bifida and its subtypes)

Types

Overview

Spina bifida can be classified according to the nature of the spinal cord defect into:

  • Spina bifida occulta – no overlying cyst
  • Spina bifida cystica – overlying skin cyst present at the affected level, divided into:
    • Meningocele
    • Myelomeningocele
    • Rachischisis

Spina bifida occulta

‘Occulta’ means hidden. Spina bifida occulta is where there is a failure of neural tube closure and is the most common type:

  • There is no visible overlying sac
  • There is no protrusion of the meninges or spinal cord
  • The overlying skin may be intact, have a patch of hair, or have a dimple

Meningocele

Meningocele is a type of spina bifida cystica where there is a cystic swelling on the back with protrusion of the meninges (dura mater and arachnoid mater). No spinal neural tissue is present and there may be no neurological signs or symptoms. 

Myelomeningocele

Myelomeningocele is a type of spina bifida cystica where there is a cystic swelling on the back with protrusion of the meninges and spinal cord (‘myelo-’). It is the second most common form of spina bifida after spina bifida occulta.

Since there is spinal cord protrusion, neurological symptoms are present.

Myelomeningocele is often associated with an Arnold-Chiari type II malformation/

Rachischisis

Rachischisis is the most severe form of spina bifida cystica where the entire spinal cord is unfused and the contents are exposed. This is associated with anencephaly and is incompatible with life. Many pregnancies end with miscarriage or stillbirth and infants that survive birth shortly die after.

Epidemiology

  • With the advent of folic acid supplementation and foetal ultrasound screening, the incidence of spina bifida has decreased

Risk Factors

Diagnosis

Overview

Most NTDs including spina bifida are detected antenatally or at birth. A general physical and neurological examination can identify the suspected level. Example features can include leg weakness, paralysis, bladder and bowel incontinence, and hip and foot deformities.

Investigations

Some key points about investigations include:

  • Maternal serum alpha-fetoprotein (AFP):
    • May be elevated at 16-18 weeks of gestation
  • Latex allergy testing:
    • Around 40% of neonates with myelomeningocele are allergic to latex
    • An ELISA or skin-prick test may be performed
  • CT/MRI of the head and/or spine:
    • May identify an associated Arnold-Chiari II malformation
    • Assesses nervous system tissue and spinal cord closure

Management

Overview

Neonates with spina bifida are managed by a multidisciplinary team. Foetal surgery or postnatal surgery may be performed to correct the spinal cord malformation.

Prevention and Folic Acid

Folic acid

A lack of folic acid is a contributing factor to the development of spinal bifida. Folic acid supplementation has reduced the incidence of neural tube defects significantly. It is important to note that drugs inhibiting folic acid metabolism should be avoided in pregnancy (such as sodium valproate or methotrexate) where possible.

Complications

  • Meningitis – due to protrusion and exposure of the meninges
  • Fractures
  • Pressure sores – due to impaired mobility
  • Hydrocephalus – due to myelomeningocele and an associated Arnold-Chiari II malformation
  • Neurogenic bladder and constipation due to impaired bladder and bowel neurology
  • Latex allergy and anaphylaxis

Prognosis

  • Early diagnosis and surgery are associated with a better prognosis
  • The long-term prognosis depends on the severity of neurological deficits

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