The spinal cord runs from the base of the brain, through the vertebrae of the back, and carries nerve messages from the brain to the body. Spina bifida is a failure of the vertebra to close over the spinal cord during development as a foetus. There are several degrees of severity:-
- Spina bifida occulta is the mildest form in which only the vertebral arch is affected, and the spinal cord works normally.
- Meningocele is more serious as there is a sac at the level of the failed fusion, which contains cerebrospinal fluid only, but the spinal cord has some damage.
- Meningomyelocele is the most serious form in which a raw, uncovered sac containing nerve tissue and cerebrospinal fluid protrudes onto the surface of the back. There is a significant risk of infection in the spine and brain and it may be associated with other birth deformities such as hydrocephalus and anencephaly (failure of the brain to develop).
The cause is unknown, but the incidence of spina bifida is higher in subsequent pregnancies after one child has been born with the condition, and in those of Irish and Welsh ancestry. The foetus develops its spinal cord and vertebrae in the first three months of pregnancy from a flat strip of nerve tissue that folds in upon itself lengthwise and fuses into a rod. It is then surrounded by the bony arch of the vertebrae. Spina bifida is the failure of the vertebral arch to form, usually in the lower back, allowing the spinal cord to be easily damaged. The unfused vertebral arch has a double pointed (bifid) appearance on x-ray examination.
Spina bifida occulta has no symptoms, but with a meningocele only some of the necessary nerve messages are transmitted to the legs and bladder causing some muscle weakness, abnormal sensations and poor bladder control. Patients with a meningomyelocele have paralysis and loss of all sensation below the level of damage and no control of the bladder or legs (paraplegia).
Mothers who are at high risk can have a test performed on the amniotic fluid that surrounds the baby in the womb between the 14th and 16th week of pregnancy to detect the defect. It may also be detected by an ultrasound scan during pregnancy. After birth, x-rays, and MRI and CT scans of the back show every detail of the defect. Folic acid supplements taken during pregnancy appear to prevent the condition.
Spina bifida occulta requires no treatment, but with a meningocele an operation to close the defect in the back is performed in childhood, while with a meningomyelocele a major operation to close the defect in the back is performed early in life, but this does not cure the paraplegia.