Neural Tube Defects
Spina
Bifida Cystica
Anencephaly,
Encephalocele, Exencephaly, Iniencephaly
Hydrocephalus
This page is only a brief overview of open neural tube defects and hydrocephalus. I don't know enough about the subject, but feel that they should be mentioned in a website on Tethered Cords. Please refer to the Information pages and Asbah for references and further information sources.
Neural tube defects are congenital birth defects. They may be classified as either aperta (open) or occulta (closed). The open forms are outlined briefly here.
Spina bifida cystica
Spina bifida is known by various names in the literature and medical world, including myelomeningocele, spina bifida cystica and myelodysplasia.
Spina bifida is caused by disturbances in the closure of the neural tube. The neural tube is the very primitive structure which develops into the brain and spinal cord. By day 17 post-conception the neural tube is formed and the spinal vertebrae begin to form around the tube. Closure of this tube to create the spinal column begins at several sites and proceeds in both directions, much like a zip. The head end closes at approximately 24 days and the bottom end in the lumbar spine area closes at about 27 days. In cases of spina bifida the spinal vertebrae fail to wrap completely around the spinal cord. The tail end of the spinal column forms by small bits of tissue coalescing to form a solid mass. This is the usual location of tethered cords. The type of spina bifida and the severity of associated disabilities depend on the location and size of the defect. The higher up the spine that the defect occurs, the more extensive the disabilities. The defect is most common in the lower thoracic, lumbar and sacral region, and may extend over 3-6 vertebrae.
This is the most common neural tube defect and often occurs before the women realises she is pregnant. Surgery on the open wound of the newborn baby is usually performed within 24 hours to close the lesion, to minimise the risk of infection and to preserve as much function as possible below the defect. The condition is often associated with hydrocephalus (see below).
The abnormalities of spina bifida include:
Disabilities caused by the defect include leg weakness or paralysis, bladder and bowel dysfunction, with the possibility of severe damage to the kidneys, and orthopaedic problems such as club feet, hip dislocations, scoliosis and kyphosis. Other problems may include Chiari Malformation, hydromyelia and tethered spinal cord.
The most severe type of neural tube defect. This takes the form of the failed closure of the neural tube at its upper end. It presents as the absence of the cranium with associated underdeveloped and/or incomplete brains in newborn babies. Neural elements are covered only by a thin membrane. Death is usual within a few hours.
Encephalocele
This is less common than anencephaly or spina bifida. It presents as a hole in the skull through which brain tissue protrudes, much like a spina bifida protrusion. This condition also has a high mortality rate of 60-75% within one year. Survivors are severely retarded.
Exencephaly
The exterioration of an abnormally formed brain.
Iniencephaly
A defect of the skull base, cervical spine and associated neural tissue.
Hydrocephalus
In the UK the best place to find information about hydrocephalus is the Asbah website. The following information is adapted from http://neurosurgery.mgh.harvard.edu and http://the-callahans.com/. This last one is a great site which follows Andrew Callahan's progress since being born with spina bifida.
What is hydrocephalus?
Hydrocephalus is an abnormal accumulation of fluid - cerebrospinal fluid or CSF - within cavities called ventricles inside the brain. CSF is produced in the ventricles, circulates through the ventricular system and is absorbed into the bloodstream. CSF is in constant circulation and has many important functions. It surrounds the brain and spinal cord and acts as a protective cushion against injury. CSF contains nutrients and proteins that are needed for the nourishment and normal function of the brain. It also carries waste products away from surrounding tissues. Hydrocephalus occurs when there is an imbalance between the amount of CSF that is produced and the rate at which it is absorbed. As the CSF builds up, it causes the ventricles to enlarge and the pressure inside the head to increase.
Hydrocephalus that is congenital (present at birth) is thought to be caused by a complex interaction of genetic and environmental factors. Aqueductal stenosis, an obstruction of the cerebral aqueduct, is the most frequent cause of congenital hydrocephalus. Acquired hydrocephalus may result from spina bifida, intraventricular haemorrhage, meningitis, head trauma, tumours and cysts. Hydrocephalus affects about one in every 500 children born.
Treatment for Hydrocephalus
There is no known way to prevent or cure hydrocephalus. To date, the most effective treatment is surgical insertion of a shunt. A shunt is a flexible tube placed into the ventricular system of the brain which diverts the flow of CSF into another region of the body, most often the abdominal cavity or a chamber of the heart, where it can be absorbed. A valve within the shunt maintains the CSF at normal pressure within the ventricles. This procedure is performed by a neurosurgeon, preferably one who specializes in paediatrics if the patient is a child.
Signs and symptoms of hydrocephalus and/or shunt malfunction include: