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The best definition of "tethered spinal cord" is that there is an abnormal attachment of the spinal cord to the tissues that surround it. The spinal cord is surrounded by a tough membrane - the dura - within which is contained the cerebrospinal fluid that surrounds and cushions the spinal cord. Any abnormal attachment of the spinal cord itself to these membranes anchors or "tethers" the spinal cord; inhibiting its normal movement within these membranes. There are several types of "normal" movement of the spinal cord that can be affected in the child and adult. With an infant's growth, the spinal cord moves upward inside the spinal canal; this movement is probably complete when the child is 6 months to a year of age. When any of us - adults included - bend, stretch, or are active in any way, our spinal cords move up and down within the spine canal as well. Tethering inhibits this movement in both cases.
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The answer to this question is not completely understood, but clinical observation as well as laboratory research has suggested several possible reasons. When the spinal cord is tethered, progressive neurological deficits can develop in a patient over time. These can include weakness of a leg or foot, the development of bowel or bladder control problems, pain in the back or legs, and even the development of curvature of the spine. We believe that these neurological problems occur because the spinal cord nerve roots at its lower end are stretched by the tethering which in turn causes progressive damage over time as this stretching continues. Some research has suggested that this stretching thins out the normal blood supply to these nerves and their nerve cells; leading to injury because the nerves aren't getting enough blood and oxygen supply. In other children, who have large fatty masses tethering their spinal cords, the sheer bulk of the fatty tissue within the spinal canal can compress the spinal cord and nerve roots compounding the injury.
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Tethering of the spinal cord in children and infants occurs because of a change in the normal development of the bottom of the spinal cord when the embryo was forming in the uterus. This is a very complicated issue, but, in brief, the normal process of development of the structures around the genital and rectal area, the bladder and the lower part of the kidneys, the bones of the lower spine, and the skin over them all develop from or are influenced by, cells in the embryo at the bottom of its primitive spinal cord. If some type of error occurs in the normal maturing of these cells, then changes can occur in any of the above-mentioned structures in the infant. This is the reason why so many children with spinal cord tethering have some type of marking on the skin of their lower back, like a dimple, an unusual hair patch, a strawberry mark, etc., and why children who are born with congenital changes in their genital organs or anus may have an associated tethered cord anomaly. There are in addition certain congenital syndromes - like the VATER or VACTERL syndromes, which involve changes in many organ systems in the newborn - which are also associated with tethered spinal cords.
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In the newborn infant, the possibility of tethering is raised by the detection of one of these unusual skin markers on the back - like a fatty lump, a small dimple, an unusual patch of hair, skin discoloration, etc. The diagnosis is further suggested in certain children, by the presence of asymmetries in the legs or feet or the presence of other congenital syndromes that are often associated with tethering - like a change in the normal anatomy of the rectum or genitalia - since, as noted above, these structures all tend to develop around the same time in the embryo. When the diagnosis is suspected in a newborn or child under the age of 4 weeks, the easiest and quickest diagnostic study to obtain is an ultrasound of the back. This test can be done without any sedation or anesthesia, and because the bones of the back are so thin at this age, the ultrasonographer can often see detail of the spinal canal that will enable a diagnosis to be made. The ultrasonographer is usually able to see where the end of the spinal cord is (a low level may indicate that the spinal cord is being pulled down by tethering), whether it is pulsating normally (no pulsations indicate that the spinal cord is being held taut by a tethering lesion), if there are fatty masses at the end of the spinal cord, if there are tracts leading from the skin down to the spinal canal, and so on.
If the child is older than one month, the ultrasound is rarely helpful and an MRI needs to be carried out to define the anatomy of the distal spinal canal. We usually wait to obtain this test until the child is 3 to 6 months of age when the risks of anesthesia are lessened and when the child is large enough so that subtle anatomical changes can be picked up. Occasionally, however, there are good reasons for proceeding with the study earlier - particularly if a tract extending from the skin down to the spinal cord itself is suspected by the presence of an eccentric dimple that appears to run deep into the tissues of the back, has a large hair or mass associated with it, or has been noted to be draining or inflamed. In these children, there is a possible risk of infection spreading from the skin to the spine canal and the development of meningitis and these children are therefore studied as soon as it is practicable.
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These tests used to be a part of the routine evaluation of these children, but they are rarely helpful except to suggest changes in bone structure which might nevertheless occur in the absence of any serious change that could cause tethering - like an incomplete closure of the bones in the back of the spine. We obtain x-rays of the spine only in special circumstances, although occasionally we request CT scans of the low back if the bone anatomy on the MRI appears very unusual and surgery is being planned.
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The bladder nerve supply comes from the very bottom of the spinal cord and is often one of the earliest affected when tethering occurs. In young children, it is very difficult to determine whether these nerves are working normally, particularly in a child who is too young to talk and not yet toilet-trained. We therefore will frequently ask our urologists to obtain a series of urodynamic studies on our patients. These tests are designed to determine how effectively the nerve supply from the spinal cord to the bladder is working. In the hands of experienced urologists, patterns of abnormal nerve impulses to the bladder can be detected and signs of spinal cord tethering diagnosed. Having these studies is particularly helpful in planning surgery, in anticipating future problems, and in counseling families about potential long-term follow-up issues.
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The basic goal of the neurosurgeon when operating on a child with a tethered spinal cord is to release the abnormal attachments to the spinal cord and reconstruct the normal anatomy of its coverings. The operation ranges from a relatively easy and quick procedure to a very difficult one with potentially serious consequences for the child. One of the most common tethering lesions - a thick fibrous or fatty filum terminale attached to the end of the spinal cord - can be treated by making a small opening between two bones of the lower spine through a small incision in the lower back, exposing the thickened filum, and simply cutting it. In these children, the risks of the surgery - in terms of healing problems, injury to normal nerves, etc -- are extremely low. In some children, the tethering lesion is a complex fatty and fibrous mass that grows through the tissues of the back into the back of the spinal cord, and replaces or enwraps nerve roots that might be supplying strength or sensation to the legs, bowel, or bladder. The surgery could therefore potentially interrupt normal nerves, causing new neurological deficits. The healing of the incision could be compromised by the congenital absence of the muscles and ligaments overlying the spinal cord, leading to poor healing, leakage of cerebrospinal fluid from the incision, meningitis, and other complications. It is important for parents to review these potential complications in detail with their neurosurgeon to be sure that they understand the risks and benefits of the proposed operation as completely as possible.
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Many surgeons monitor the function of the nerves of the legs and bowel and bladder by various monitoring techniques during the operation, and constantly stimulate structures in the area of the surgery to make sure that they are identified and that no normal structures are divided during the surgery. We monitor the electrical signals coming from the muscles around the rectum during surgery - since nerves that supply the rectum also supply the bladder -- and drape our patients with transparent drapes so that we can see and feel contractions of their muscles while we operate. Certain technical advances, such as the contact YAG laser, can help to reduce the bulk of fatty masses while limiting harmful traction and manipulation of the spinal cord. The operating microscope is used for virtually all of these untethering operations.
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This answer also depends on what type of operation is done. In the case of the section of a filum terminale, the children are in the hospital only 2 to 3 days. The patients have pain after the operation and often need narcotic medication for a day or two to keep them comfortable. A day or two of fever is quite common and the children often have no real appetite during this period. Many neurosurgeons also prefer to keep their patients flat for a day or two so that the healing of the incision is promoted and the surgical incision is not stressed. In the case of surgery on a large fatty mass (lipomeningocele, spinal lipoma, etc.), much more caution regarding wound healing must be observed because of the risk of cerebrospinal fluid leak through areas where the dura was reconstructed with a graft or through layers of back tissue that could only be closed tenuously. Many of these children are in the hospital for at least a week and occasionally go home to lie in bed for an extended period after discharge.
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In the case of a simple and straightforward operation - like the section of a filum - many neurosurgeons follow these youngsters yearly until they are walking and toilet trained and then discharge them. There is usually very little risk that scarring will cause the spinal cord to retether in these children. In complicated lesions, however, there is a certain risk that scarring may occur and lead to retethering. This likelihood is strongest when there is a complex lipoma at the base of the spinal cord or when there are bony changes in the spine canal that split the spinal cord in two (diastematomyelia or split cord malformation) or other similar rare complex lesions. In our own data, this risk of retethering can be as high as 15 to 20% over the first two decades of the child's life in the more complicated lesions. There appear to be two peak periods when this retethering tends to occur in our patient population - between ages 4 and 6, and from ages 8 to 13 - probably because of growth spurts during these ages. We follow children with complex lesions yearly or every other year until they are adults, often in a clinic (spina bifida clinic) where other specialists, such as urologists, orthopedic surgeons, and pediatricians are present to also help monitor the child's progress.
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Neurosurgeons at The Children's Hospital Boston have extensive experience treating children with these congenital disorders of the spinal cord, and take care of hundreds of these children every year.
Please feel free to contact any of us in the Pediatric Neurosurgical Department if you have additional questions.
R. Michael Scott, M.D.
Edward R. Smith, M.D.
Liliana C. Goumnerova, M.D.
Joseph R. Madsen, M.D.
Mark R. Proctor, M.D.
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Children's Hospital Boston
Department of Neurosurgery
300 Longwood Ave
Boston, MA 02115
PHONE: 617 355-6008
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R. Michael Scott
Edward Smith
liliana gourmnerova
joseph madsen
mark proctor
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