This article is published by the Pediatric Section of the American Association of Neurological Surgeons and Congress of Neurological Surgeons. It is one in a series covering pediatric neurosurgical topics. It has been written and edited by members of the society. This article is sponsored by the Section as a service to parents. Its purpose is to help you understand the complexities of the condition described. It is hoped that with a better knowledge of the condition, you will have a better understanding of what your child’s physician has explained to you. In doing so, you will be better able to ask any questions you may have. At the end of this article is a glossary of medical terms to refer to is a word, test, or procedure in the text is not understood. Understanding the terms will help you to understand the condition. In addition a list of support groups is included after the glossary for further information and assistance.
The vertebral column, which is made up of the vertebrae and the laminae and spinous processes is a bony canal which holds the spinal cord. The spinal cord normally “floats” in a fluid filled sac called the thecal sac (or dural tube). The spinal fluid surrounds the spinal cord so that the cord itself does not touch the surface of the sac. The spinal cord normally ends at around the first or second lumbar vertebrae. Below this level is the cauda equina which is a “tail” of nerves that will go on to supply the legs and the bowel and bladder. These nerves, as well as those to the arms, travel through a space in the bones called a foramen. From there they travel to the muscle or skin that they innervate. Each nerve goes to a particular area of the skin or to a particular muscle. Sensory nerves go to the skin to give us the ability to feel things. Motor nerves go to the muscles to allow us to move our muscles. These is some overlapping of the nerves, so that one muscle or one area of skin is usually supplied by more than one nerve.
During development, the spinal cord and nerves do not always form correctly and the result can be spina bifida. There are many forms of spina bifida. In the mildest form, the bones to not form a complete ring around the spinal cord, but the spinal cord itself is normal. This is called spina bifida occulta and this occurs in about 2% of the population. More serious forms of spina bifida occur at a rate of about 1-5 per 1000 live births. This is often referred to as myelomeningocele. When this congenital malformation occurs, the spinal cord is open on the back without skin covering it. An operation has to be done at birth to replace the spinal cord within the thecal sac and cover it with muscle and skin. Children born with myelomeningocele are at particular risk of developing a tethered cord later in life. Other types of tethered cord include lipomyelomeningocele, low conus and diastematomyelia. In some cases the filum terminale is too tight or has too much fact in it, and this can cause a tethered cord. Sometimes the back looks fairly normal, but there are some signs that can be seen in the skin overlying the spin that may suggest an underlying problem with the spinal cord. We call these abnormalities neurocutaneous stigmata, meaning they are a sign that there is a problem with the spinal cord underneath. They include: hemangiomas, a tuft of hair, a dimple or small hole, a fatty lump of tissue, or even a “tail.” A child with a history of myelomeningocele or one of the neurocutaneous stigmata over their spine is at risk of having a tethered spinal cord.
The symptoms of tethered cord can vary. One common problem is difficulty walking or weakness in the legs or feet which may cause the leg to drag or the feet to turn in or out. Pain in the back or legs is also common. Other changes include numbness or tingling, a change in bladder or bowel such as wetness between catheterizations, scoliosis (curved spine), “tight” or stiff legs, tenderness over the spine or previous scar, and a decrease in activity. If your child develops symptoms such as these, they should be evaluated for the possibility of a tethered cord.
If a tethered cord is suspected, one or more tests may be necessary to confirm the diagnosis. An MRI scan is usually the first test to be ordered, because this is not invasive and can make the diagnosis. Other tests may be performed as well. If the MRI scan does not confirm the tethered cord for ceratin, a myelogram may be necessary. This is a special test that involves a spinal tap to put dye into the thecal sac. Plain x-rays and a CAT scan of the spine are taken after the myelogram to see how the dye flows around the spinal cord and nerves. Most children need general anesthesia for this test. Sonography is another test that is sometimes useful. It is a sound wave test that helps the doctors see how the spinal cord moves in the thecal sac.
If a tethered cord is present, surgery is then recommended. The operation involves removing some bone to get to the thecal sac and then separating the connection between the spinal cord and the thecal sac. After the operation, there is about a 15-20% chance that the tethered cord could develop again sometime in the future. This is why it is important to follow-up with your neurosurgeon. She or he may notice something while examining your child that you don’t see at home. Since the operation can only stop the progression of symptoms d not repair any damage that has occurred from the tethered cord, it is important that it be diagnosed and treated as early as possible.
Frequently asked questions
Why is a tethered cord a problem?
When the spinal cord is tethered it can cause damage to the spinal cord as the child moves or grows. Over time, blood vessels become stretched and the blood flow to the spinal cord decreases. If the spinal cord doesn’t receive enough blood, it can be permanently damaged. Over time, damage to the spinal cord can result in permanent weakness in the legs, problems with bowel and bladder function, changes in the ability to feel things in the legs (which may result in the development of pressure ulcers) and curvature of the spine. Children who are still growing are especially at risk of developing increased problems because of a tethered cord. That is why it is important to know what problems your child might develop that suggest a tethered cord.
Who gets tethered cords and why?
Tethered cord is most often found in children with spina bifida, myelomeningocele and lipomyelomeningocele. This is because these children have often had surgery in the past. In children with spina bifida, the spine, spinal cord and thecal sac did not develop normally. Even with surgery, the doctor cannot make it completely normal. Also, surgery causes some scarring which can make the spinal cord stick to the thecal sac over time. Other children can have a tethered spinal cord, but this is much less common.
The doctor said I have a tumor in my spine causing the tethered cord. What does that mean?
Sometimes when the spinal cord does not develop normally, a piece of skin gets inside the spinal cord. Over time, the piece of skin can grow in size (it “sheds” just like skin outside does) and forms a dermoid or an epidermoid. Sometimes fat in the spinal cord is also called a tumor. The ‘tumors” are not cancer, but because it is tissue that does not belong in the spinal cord, it is called a tumor. These can often be removed at surgery, but they can recur.
CAT scan: A special type of x-ray that shows the spinal column very well. When dye has been placed in the thecal sac with a myelogram, the two tests together help show a tethered cord.
Cauda equina: The collection of nerve below the end of the spinal cord which travel down the thecal sac to leave through the foramen to go to the muscles and skin.
Conus: The tip of the spinal cord. This part of the spinal cord supplies nerves to the bowel and bladder primarily.
Dermoid/Epidermoid: A piece of skin that gets caught below the skin and enlarges to form a tumor. This is not cancer, but tissue located in a place where it doesn’t belong, such as in the spinal cord.
Filum: This is a thin piece of tissue that comes from the end of the spinal cord and goes to the tail bone. Sometimes there is too much fat in the filum, or the filum is too tight. Both of these things can cause a tethered cord.
Hemangioma: A collection of small blood vessels that can appear like a red spot in the skin.
Lipomyelomeningocele: A special type of spina bifida where the conus is filled with fat and the fat goes outside the thecal sac to connect to fat below the skin.
MRI: A special type of study that uses a strong magnet to show doctors details about the spinal cord or other parts of the body.
Myelogram: A special type of x-ray study that involves a spinal tap to inject dye into the thecal sac. X-rays and CAT scans are usually taken after the spinal tap to better show the spinal cord and the nerve roots.
Myelomeningocele: A congenital abnormality where the spinal cord does not roll up into a tube the way that it normally does. The spinal cord stays on the surface of the skin. The nerves that are below the level where the spinal cord stopped rolling up do not work properly.
Sonogram: A sound wave study that helps show is the spinal cord _______ normally. This is like the sonogram or ultrasound that pregnant women have done.
Spina bifida: This literally means “open spine.” It can be a mild form, where only the bones are open and the spinal cord is normal, or the spine can be open on the top of the skin.
Thecal sac (dural tube): This is the tube which holds the spinal cord and the spinal fluid.
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©2000 AANS / CNS Section on Pediatric Neurosurgery
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