Spina Bifida and Tethered Spinal Cord

Tethered Spinal Cord
At birth, the spinal cord is normally located opposite the disc between the first and second lumbar vertebrae in the upper part of the lower back. In a baby with spina bifida, the spinal cord is still attached to the surrounding skin, preventing it from ascending normally, so the spinal cord is low-lying or tethered. Although the skin is separated and closed at birth, the spinal cord stays in the same location after the closure. As the child continues to grow, the spinal cord can become stretched, causing damage and interfering with the blood supply to the spinal cord. This can result in back pain, leg pain, changes in leg strength, progressive or repeated muscle contractions, orthopedic deformities of the legs and scoliosis, and bowel and bladder problems. A definitive diagnosis of a tethered spinal cord is made through diagnostic tests.

The shunt is checked through a computed tomography (CT or CAT scan) or magnetic resonance imaging (MRI). In some cases, the shunt is tapped to assess shunt function. If there is any question about shunt function, the neurosurgeon may explore or revise the shunt, before considering operating on the spinal cord.

If the shunt is working well, usually an MRI of the spine is done to exclude other problems. Additional studies such as a Manual Muscle Test (MMT) and special bladder studies (urodynamics) may be prescribed. These will be compared with prior studies to assess changes and to give a baseline against which to compare after the surgery. Untethering is generally performed only if there are clinical signs or symptoms of deterioration.

The surgery involves opening the scar from the prior closure down to the covering (dura) over the myelomeningocele. Sometimes a small portion of the bony vertebrae (the laminae) are removed to obtain better exposure or to decompress the spinal cord. The dura is then opened, and the spinal cord and myelomeningocele are gently dissected away from the scarred attachments to the surrounding dura. Once the myelomeningocele is freed from all its scarred attachments, the dura and the wound are closed.

The child usually can resume normal activities within a few weeks. Recovery of lost muscle and bladder function depends upon the degree and length of preoperative implications. The combined complication rate of this surgery is usually only 1 to 2 percent. Complications include infection, bleeding, damage to the spinal cord or myelomeningocele, which may result in decreased muscle strength or bladder or bowel function. Many children require only one untethering procedure. However, since symptoms of tethering can occur during periods of growth, 10 to 20 percent require repeated surgery.

Prevention
Women of childbearing age can reduce their risk of having a child with spina bifida by taking 400 micrograms (mcg) of folic acid every day. Because it is water soluble, folic acid does not stay in your body for very long, and needs to be taken every day to be effective against neural defects. Since half of all pregnancies in the United States are unplanned, folic acid must be taken whether a woman is planning a pregnancy or not. Research has shown that if all women of childbearing age took a multivitamin with the B-vitamin folic acid, the risk of neural tube defects could be reduced by up to 70 percent

NeurosurgeryToday.org
September, 2005

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