Spina Bifida is a fault in the spinal column in which one or more vertebrae (the bones which form the backbone) fail to form properly, leaving a gap or split, causing damage to the central nervous system. To help understand what it is, let us explain about the composition of the nervous system.
The central nervous system consists of the brain and the spinal cord. All activities are controlled by the brain which receives information from touching, seeing, feeling, tasting and hearing - responding to this information by initiating the appropriate movements of different parts of the body. Messages from the brain are carried to different parts of the body by the spinal cord which runs down the centre of the spinal column. This communication system for the body is very important and needs protection
The spine is made up of 33 bones or vertebrae. The vertebrae have two main functions. One is to provide anchorage for muscles so that we can move as we dictate to those muscles. The other is to provide protection to the spinal cord.
The central nervous system and spine develop between the 14th and 28th day after conception. Spina bifida occurs when there is a failure of development of the boney canal which surrounds the brain and spinal cord. In the spine, the affected vertabrae have a defect posteriorly (at the back) so that a boney ring does not completely surround the spinal cord. This leaves a gap so that, instead of the posterior arm being whole it is divided - that is bifid. The fault may occur in one or more of the vertabrae but it is most common around waist-level.
There are three main types of spina bifida :
This is a very mild and common form and very rarely causes disability. There is a slight deficiency in the formation of (usually) one of the vertebrae. It may have visible signs of a dimple or small hair growth on the back. However, many people are unaware that they have spina bifida occulta as they have no symptoms or signs.
Many people have this condition. One survey suggested the proportion could be one in 10 of the population. The vast majority of these will have no symptoms or problems.
Spina bifida occulta may be detected by X-ray when, for example, investigations of back injury are being made. In such cases, it can be extremely frightening to be labelled as having spina bifida butit must be emphasised that, for the vast majority, it is of no consequence whatsoever.
Women with spina bifida occulta should ask their doctor to prescribe the higher dosage of folic acid when they plan to become pregnant - to help reduce the risk of their baby being affected by spina bifida.
Unfortunately, in some cases the cleft in the spine may cause problems. Sometimes the spinal cord may become tethered - that is, caught against the vertebrae. With growth, tension can cause inefficient functioning, affecting bladder control and mobility.
If these symptoms are observed, it is important to consult a GP who, if appropriate, can refer to a neurosurgeon.
The visible signs are a sac or cyst, rather like a large blister on the back, covered by a thin layer of skin.
In this form, the sac contains tissues which cover the spinal cord (meninges) and cerebro-spinal fluid. This fluid bathes and protects the brain and spinal cord. The nerves are not usually badly damaged and are able to function, therefore there is often little disability present. This is the least common form.
Myelomeningocele is the most serious and more common of the two forms of cystic spina bifida. Here the cyst not only contains tissue and cerebro-spinal fluid but also nerves and part of the spinal cord. The spinal cord is damaged or not properly developed. As a result, there is always some paralysis and loss of sensation below the damaged region. The amount of disability depends very much on where the spina bifida is and the amount of nerve damage involved. Many people with this condition have bowel and bladder problems because of damage to the nerves going to the bowel or bladder from the bottom end of the spinal cord.
This is a sac which is formed when the bones of the skull fail to develop. It may contain cerebrospinal fluid only, however, part of the brain may also be present in the sac, resulting in brain damage.
This is where the brain does not develop properly or is absent, and the baby is either still born or dies shortly after birth.
Most babies born with spina bifida also have hydrocephalus (from the Greek hydro = water, cephalie = brain). This is an accumulation of cerebrospinal fluid which arises from an imbalance in the production and drainage of that fluid.
At present, the cause is unknown, although research continues. Our page on folic acid outlines the research results which led to the Department of Health issuing guidelines about the part that folic acid supplements play in reducing the risk of spina bifida in pregnancy, provided they are taken daily from at least one month before conception and then through to the end of the 12th week of pregnancy.
The exact reasons why the tube develops incorrectly are not yet known but it is probably connected with both genetic and environmental factors.
Spina bifida is a defect which is present at birth. In Britain, incidence varies from one area to another. Spina bifida is only partially hereditary. However once there has been as affected pregnancy, there is an increased risk of further spina bifida pregnancies. The risk of an adult with spina bifida having a child with a similar condition is approximately 3% or 1 in 35.
