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Conditions · Spine

Spina bifida (myelomeningocele) !

Spina bifida (myelomeningocele) is a birth defect where the spine does not close and the spinal cord pushes out in a sac on the back.

Updated 2026-10-29

Structures involved

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In biochemistry

In embryology

Why it happens

What it is

Neural tube defect in which the vertebral arches fail to close and the spinal cord and its coverings protrude through an open sac on the back. It is the most severe form of open spina bifida.

Who gets it

One of the most common congenital defects of the nervous system. Rates have fallen in countries that fortify flour with folic acid, including several in Latin America.

Causes

  • Failure of the caudal neural tube to close in the first month of pregnancy
  • Multifactorial: genetic and environmental factors combined

Risk factors

  • Low maternal folate
  • Previous pregnancy with a neural tube defect or a family history
  • Maternal diabetes and obesity
  • Some antiseizure drugs in pregnancy, such as valproate
  • Maternal fever or hyperthermia in early pregnancy

Pathophysiology

The exposed neural tissue is malformed and is further damaged in the womb by amniotic fluid and trauma. Loss of function below the level causes weakness and sensory loss of the legs and neurogenic bladder and bowel. Leakage of cerebrospinal fluid pulls the hindbrain downward (Chiari II malformation), which blocks fluid flow and causes hydrocephalus.

Classification

  • Spina bifida occulta: closed bony defect, often with no symptoms
  • Meningocele: sac with meninges and fluid but no neural tissue
  • Myelomeningocele: sac containing spinal cord or nerve roots
  • By level: thoracic, lumbar or sacral; higher lesions cause more deficit

Symptoms and signs

  • Open sac on the back, most often lumbosacral, seen at birth or on prenatal ultrasound
  • Leg weakness or paralysis and loss of sensation below the level
  • Foot and hip deformities (clubfoot, hip dislocation)
  • Neurogenic bladder and bowel
  • Signs of hydrocephalus: large head, bulging fontanelle
  • Brainstem signs from Chiari II: feeding problems, stridor, apnoea

Diagnosis

Clinical
Inspection of the back at birth and full neurological exam to define the functional level; head circumference and fontanelle checks.
Tests
Maternal serum alpha-fetoprotein screening in pregnancy (raised in open defects). Urodynamic studies and renal function after birth.
Imaging
Prenatal ultrasound shows the defect and skull signs (lemon sign) and cerebellar signs (banana sign); fetal MRI adds detail. After birth: head ultrasound or MRI for hydrocephalus and Chiari II, spine MRI, and kidney ultrasound.

Differential diagnosis

  • Meningocele or lipomyelomeningocele
  • Sacrococcygeal teratoma
  • Spina bifida occulta
  • Other congenital spinal masses

Goal of treatment

Close the defect to prevent infection and further damage, control hydrocephalus, and support lifelong function of the kidneys, bladder, bowel, limbs and learning.

Treatment

Surgical
Surgical closure of the defect within the first days after birth, with the sac kept moist and covered and infection prevented until then; fetal repair in selected pregnancies at specialised centres reduces the need for a shunt.
Surgical
Treatment of hydrocephalus with a ventriculoperitoneal shunt or endoscopic third ventriculostomy.
Follow-up
Lifelong follow-up by a team: urology (clean intermittent catheterisation, bladder medicines), bowel programme, kidney checks, and surveillance for tethered cord and scoliosis.
Rehabilitation
Rehabilitation and orthopaedics: physiotherapy, braces and mobility aids, care of the feet and hips, and school and psychosocial support.

Drugs for this condition

Complications

  • Shunt failure or infection
  • Urinary tract infections and kidney damage
  • Tethered spinal cord
  • Scoliosis and hip dislocation
  • Latex allergy
  • Pressure sores and fractures in areas without sensation
  • Learning difficulties

Prognosis

Most children survive into adulthood with good care. Function depends on the level of the lesion and on hydrocephalus; kidney protection and shunt care are key to long-term health.

Prevention

  • Folic acid supplementation for all women who could become pregnant, starting before conception (higher supplementation after an affected pregnancy, as guidelines set)
  • Folic acid fortification of staple foods such as flour, a proven public-health measure
  • Control of maternal diabetes and review of medications before pregnancy

Test yourself

Think of the answer, then tap the question to see it.

Which public-health measure has reduced the frequency of neural tube defects?

Folic acid supplementation before conception and fortification of staple foods such as flour with folic acid.

Which brain malformation is almost always associated with myelomeningocele?

Chiari II malformation, with downward displacement of the hindbrain.

Why do many children with myelomeningocele develop hydrocephalus?

The Chiari II malformation blocks the flow of cerebrospinal fluid out of the brain's ventricles.

What do the lemon and banana signs on prenatal ultrasound suggest?

Open spina bifida: a lemon-shaped skull and a banana-shaped cerebellum from the Chiari II malformation.

Why are children with spina bifida managed in a latex-free environment?

They have a high risk of latex allergy from repeated early exposure during surgery and catheterisation.

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Educational information, not medical advice. For any symptom, see a health professional.

Sources: Myelomeningocele (StatPearls (NCBI Bookshelf), 2024).

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Representative model, for educational purposes only.

Spinal cord highlighted on the Durgical 3D model