Spina Bifida Overview

The human nervous system develops from a small, specialized plate of cells (the neural plate) along the back of an embryo. Early in fetal development, the edges of this plate begin to curl up toward each other, creating the neural tube -- a narrow sheath that closes to form the brain and spinal cord of the embryo. As development progresses, the top of the tube becomes the brain and the remainder becomes the spinal cord. This process is usually complete by the 28th day of pregnancy. But if problems occur during this process, the result can be brain disorders called neural tube defects, including spina bifida.

What is Spina Bifida?

Spina bifida (Latin: "split spine") is a developmental congenital disorder caused by the incomplete closing of the embryonic neural tube. Some vertebrae overlying the spinal cord are not fully formed and remain unfused and open. If the opening is large enough, this allows a portion of the spinal cord to protrude through the opening in the bones. There may or may not be a fluid-filled sac surrounding the spinal cord. Other neural tube defects include anencephaly, a condition in which the portion of the neural tube that will become the cerebrum does not close, and encephalocele, which results when other parts of the brain remain unfused.

Spina bifida can be surgically closed after birth, but this does not restore normal function to the affected part of the spinal cord. Intrauterine surgery for spina bifida has also been performed, and the safety and efficacy of this procedure are currently being investigated. The incidence of spina bifida can be decreased by up to 70% when the mother takes daily folic acid supplements prior to conception. This was a study done on mothers who already have a child with spina bifida.

Spina bifida progresses from a cleft, or splitlike opening, in the back part of the backbones (the spinal vertebrae). In more severe cases, it involves the spinal cord. Spina bifida is the most common of a group of birth defects known as neuraltube defects, which affect the central nervous system (brain and spinal cord).

Spina bifida begins in the womb, when the tissues that fold to form the neural tube do not close or do not stay closed completely. This causes an opening in the vertebrae, which surround and protect the spinal cord. This occurs just a few weeks (21 to 28 days) after conception—usually before the woman knows that she is pregnant.

The three most common types of spina bifida are: 

• Spina bifida occulta: “Occulta” means hidden, and the defect is not visible. Spina bifida occulta is rarely linked with complications or symptoms. Spina bifida occulta is usually discovered accidentally when the person has an x-ray or MRI for some other reason. The prevalence of occulta is not known, but it is probably the most common type of spina bifida. Estimates of prevalence from 5% to as high as 40% have been proposed.
• Meningocele: The membrane that surrounds the spinal cord may enlarge, creating a lump or “<cyst.” This is often invisible through the skin and causes no problems. If the spinal canal is cleft, or “bifid,” the cyst may expand and come to the surface. In such cases, since the cyst does not enclose the spinal cord, the cord is not exposed. The cyst varies in size, but it can almost always be removed surgically if necessary, leaving no permanent disability. This is an uncommon type of spina bifida.
• Spina bifida cystica (myelomeningocele): This is the most complex and severe form of spina bifida. Spina bifida cystica usually involves neurologicalproblems that can be very serious or even fatal. A section of the spinal cord and the nerves that stem from the cord are exposed and visible on the outside of the body. Or, if there is a cyst, it encloses part of the cord and the nerves. This condition, which was documented 4000 years ago, accounts for 94% of cases of true spina bifida.

The term “spina bifida” often is used interchangeably with myelomeningocele, since this is the type of spina bifida that causes the vast majority of disability. Fortunately, surgery is an effective treatment in most people with spina bifida. Most infants with an open spine or myelomeningocele undergo surgery within the first 48 hours of life to close the defect. Antibiotics are given to prevent infection of the exposed spinal cord and nerves until these structures can be protected by surgery.
  
Before antibiotics were available, most children born with myelomeningocele died soon after birth. Those who survived were severely disabled. With modern treatment, almost all children with myelomeningocele survive and most are able to live productive lives with some degree of independence. Even with these treatments, however, most have some degree of permanent leg paralysis and often difficulties with bowel and bladder function. The extent of paralysis depends on which part of the spinal cord is involved. The higher the defect on the body, the more severe the paralysis. About 80% of myelomeningoceles occur in the lumbar(lower back) and sacral (tailbone) regions of the spine. 

Spina bifida is one of the most common severe birth defects, historically occurring in 1 live birth per 1000 in the United States. The rates of spina bifida are higher in Hispanics and whites of European descent than in Ashkenazi Jews, Asians, and African Americans. Rates are also higher among mothers with certain health problems, such as diabetes or seizure disorders (taking certain anticonvulsants), and significantly higher among couples in which at least one has spina bifida, and among couples who have already had a child with spina bifida. 

The outlook for spina bifida has improved remarkably in the last decade. Not only have advanced surgical techniques improved quality of life for people born with spina bifida, but evolving approaches to early diagnosis have even opened the possibility of corrective surgery while still in the womb. Furthermore, studies completed in the 1990s showed that as many as 70% of cases of neural tube defects could be prevented by adequate intake of folic acid immediately before and in early pregnancy. A rigorous program of public education and fortification of popular foods with folic acid in the United States has decreased the rate of neural tube defects by about 20% in just a few years.