Spina bifida in its strictest sense means defective fusion of the vertebral posterior elements, leading to a bifid osseous configuration of the spine 16. However, most commonly it is used as a synonym or subset of spinal dysraphism.
The estimated incidence is at 1:1000-2000 live births 2.
A constellation of features can occur and these depend on the severity of spina bifida and any associated CNS defects. Common symptoms include:
- back pain
- bladder or bowel incontinence
- spinal or lower limb deformities
Spina bifida is failure of the normal development of the neural tube. The etiology is often multifactorial with both genetic and environmental factors considered to play a role. Intake of adequate amounts of folic acid plays a protective role.
There are many ways of classifying a spina bifida. One method is according to the extent of the defect and is as:
- spina bifida aperta/spina bifida operta: defect can be open or closed (commoner)
- spina bifida occulta: mildest form
Another method is based on the position, either anterior (ventral) or posterior (dorsal). The vast majority of cases are of dorsal spina bifida.
A spina bifida can also be subtyped as:
- open: (80-90%) especially if detected antenatally 4
- closed: if covering skin present
While it can occur anywhere along the spine 14:
- lumbosacral region (90%)
- cervical region (2-3%)
- maternal alpha fetoprotein (MSAFP): elevated in 80% of open spina bifida (and normal in most fetuses with closed spina bifida) 15.
Associated anomalies can occur in up to 40% of cases (especially if detected antenatally). They include:
- aneuploidic syndromic
- non-aneuploidic syndromic
- CNS anomalies
- limb anomalies
- valproate embryopathy
- neurenteric cysts: particularly with ventral spina bifida
Ultrasound generally has a high detection rate for spina bifida and may show dorsal ossification centers / lateral pedicles as being splayed apart (which can give a V-shaped appearance to the posterior elements).
Ancillary intracranial sonographic findings:
- lemon sign: considered to have a strong association with spina bifida 2
- banana sign: the appearance of the cerebellum wrapped around the medulla as part of a Chiari malformation
Notably, closed and skin covered spinal lesions typically do not have any associated cranial abnormality. A normal cranial ultrasound therefore does not exclude a neural tube defect.
Treatment and prognosis
The overall prognosis is variable depending on the type and extent. For an isolated spina bifida, the recurrence risk range for future pregnancies is thought to be around 0.3-5% 12,13. Maternal intake of folic acid in subsequent pregnancies may again reduce the risk significantly.
- lower limb dysfunction
- development of neurogenic bladder 10
History and etymology
The term spina bifida derives from the Latin words: bifida = split and spina = spine.
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Related Radiopaedia articles
Congenital spinal abnormalities
- spinal dysraphism
- Chiari malformations