Types of Neural Tube Defects
Spina bifida, is the most common type of NTD. It occurs when the neural tube does not close completely somewhere along the backbone/spine. Symptoms vary from person to person and can change over time. They tend to occur below the defect and may range from few or none, to partial or total lower body weakness, loss of feeling, or paralysis. Complications will also vary. Cases of spina bifida are generally classified as either “closed” where the skin covers the defect or as “open” where the skin is not intact. Variants include:
Closed Neural Tube Defects
Spina Bifida Occulta
Spina bifida occulta is often called hidden spina bifida. A small gap may exist in one or more of the bones of the spine, but the spinal cord and tissues are normal. Many people with this condition do not have any symptoms and may never know that it exists unless it is identified during testing that is done for another reason.
Closed neural tube defects are frequently grouped with spina bifida occulta. They consist of a wide variety of spinal defects with malformed bone, tissue, and/or fat deposits at the location of the defect. Often there is a visible sign on the outside of the baby’s skin. This may be a tuft of hair, a dimple, a birthmark, lump, or skin opening. Many patients with this condition will have few symptoms, but some may have nerve damage that affects normal bowel or bladder function and/or can cause lower body weakness and pain.
Open Neural Tube Defects
With this type of spina bifida, cerebrospinal fluid (fluid from around the brain) and meninges (membranes covering brain) have ballooned out of the spinal opening to form a bulge or sac, but the spinal cord is usually in its normal location. This bulge may or may not be covered with a layer of skin. This bulge will be noticeable on the back of the baby. Symptoms are variable.
This is the most severe type of spina bifida. It develops when the cerebrospinal fluid, meninges, and the spinal cord protrude through the opening in the spine. It leaves the spinal cord vulnerable to damage and can cause paralysis in those parts of the body below the opening. Affected patients frequently have bowel and bladder problems. Some will require assistance to walk and others will require a wheel chair. Newborns with this condition are at an increased risk of developing meningitis.
Up to 80 to 90 percent of people with spina bifida will develop hydrocephalus. This occurs when the flow of cerebrospinal fluid is blocked and builds up in the brain. The child’s head becomes larger and there is increased pressure on the brain. Left untreated, this condition can cause mental retardation and learning disabilities and can in some cases be fatal. Hydrocephalus is usually treated by putting in a tube called a shunt that allows excess cerebrospinal fluid to drain into the abdomen (tummy).
Anencephaly is the term used for an NTD that affects the head. The result is the lack of development of a large portion of the brain and skull. Some babies affected are stillborn. Those that are born alive are usually unconscious, unable to feel pain, deaf, and blind. Most of those affected die within a few hours or days.
There are a variety of other, rarer forms of NTDs. All are associated with a lack of proper neural tube formation.