The Amphitheater
On-line Lectures
Tethered Cord Syndrome: Questions and Answers
(To view our previous lectures, click
here)
by Joseph R. Madsen,
MD
A recent On-line Lecture by Dr. Joseph Madsen on the treatment of
spasticity generated a large amount of e-mail from a news group interested in
adult tethered cord syndrome. Prompted by this response, Dr. Madsen has written
a lectureon the topic in general and to addresses those questions.
In human develop, the spinal cord begins as a tube made from the surface
layer of the embryo called the ectoderm. This tube buds off, sinks below the
surface of the skin and is surrounded by connective tissue which becomes the
spinal covering (dura) and the bones of the spine. The tube closes from head to
tail, much like a zipper. The very tail end of the spinal cord forms somewhat
differently by small bits of tissue coming together to form a solid mass.
Tethering abnormalities generallly occur in this part of the spinal cord.
As the embryo develops, the spinal cord and the bones surrounding it grow at
different rates and, over time, the bones grow longer than the spinal cord.
While the base of the bones and the tail end of the spinal cord start out
together, by the time of birth the end of the spinal cord is at the first or
second level of the lumbar vertebrae, just a bit below the rib cage. Tethered
cord syndrome, however, occurs if the spinal cord becomes caught, or tied down
during this bone growth by scar tissue, a fatty mass (lipoma) or a developmental
abnormality. Effectively, this stretching of the cord can cause damage.
Patients usually experience problems with tethered cord syndrome after a
growth spurt. They may have difficulty with urinary, bowel or bladder control,
feet deformities, difficulty walking or low back pain. If lower nerve roots of
the patient are involved it can cause a Òlower motor neuron problemÓ.
In this case the muscles controling the bladder or legs, for example are weak
and relatively flaccid. If the damage is mostly in the spinal cord there may be
an Òupper motor neuron problem,Ó which results in spasticity.
Visible symptoms of tethered cord syndrome include abnormalities on the skin at
the base of the cord such as a tangle of blood vessels (hemangioma), a hairy
patch or an abnormally placed dimple. Sometimes the mass of fatty tissue or
lipoma is evident right under the skin. MRI scans may reveal fat deposits in the
tiny filament that usually comes out of the end of the spinal cord.
Evaluating patients with these problems begins with a detailed neurological
examination and often includes an MRI scan which shows the the cord tissue and
lipomas, a CT scan to show bones which may also be abnormal, a pressure study or
electrical study of the bladder, and sometimes specialized studies of the anal
sphincters. In small children, we often obtain electrical studies of the bladder
sphincters which outline very specific reflexes because these indicators can
tell something about how well the neurological machinery is working, even in a
child not yet toilet trained. If there are abnormalities in the legs or feet,
orthopedic evaluation is also recommended.
The surgical treatment for the tethered cord syndrome is generally to
untether the cord whenever there is evidence that the neurological situation can
be improved or stabilized by doing the surgery. It is therefore quite important
to have a sense of whether the symptoms are getting worse, are stable, or are
getting better with time prior to making a decision about surgery. These can be
some of the most complex and vexing problems in neurosurgery.
With this introduction, we will go on to some of the questions raised by the
adult tethered cord interest group.
Q: Is laser surgery an option in removing the lipoma?
JRM: Lasers can sometimes vaporize the fat tissue which makes up a
spinal lipoma and they can be quite useful in debulking a large mass or in
melting the lipoma around the nerve roots without retracting on them. This is
probably one of the most advantageous uses of lasers in neurosurgery. However, I
would note that many people think that Òlaser surgeryÓ is a
noninvasive procedure, perhaps mixing it up with radiosurgery, a method of
giving radiation therapy which does not involve cutting the skin. Laser surgery
in this case is an adjunct used in the operating room during a normal surgical
procedure.
Q: Is there anything that would assist the doctor during surgery so
nerves wonÕt be damaged?
JRM: Depending on the nature of the case, several techniques can be
used to identify the nerve roots and try to preserve them. Some of the most
useful techniques involve electrically stimulating the nerve. These tests are
similar to those used in rhizotomy (see prior on-line lecture) but in addition
to electrical signals from muscles, direct observation of movements in the legs
and feet can be very useful. Special anesthesia techniques need to be done to
allow this kind of testing. In addition, some protocols involve more extensive
use of tools to gather information from the urinary and rectal sphincters at the
time of surgery.
Q: I would like to know how the surgeons choose between mesh and
tissue transplants for closing the dura during untethering surgery.
JRM: A range of materials have been suggested and tested to close
the defect while preventing spinal fluid (CSF) leakage or the risk of the cord
retethering. CSF leakage, which can cause serious infection, can occur when the
tissue patch over the dura is not Òwater-tightÓ. Retethering, or
restriction of the normal movement of the cord within its covering, results from
scar tissue between the remnant of the spinal cord tissue and the patch used to
close the dura. It is certainly safe to say that there is no single answer to
these complicated problems and no single material which will prevent them.
Tissue taken from the patientÕs own body (such as other connective tissue
surfaces or the soft tissue right outside the skull) is often well tolerated but
may involve additional complications or separate incisions to obtain them. Other
products are available including protein containing materials from human
cadavers, animal tissues, synthetic polymers and plastics. Each individual
surgeon will make a decision on the patch material based on his or her
experience. It is quite reasonable to discuss how these choices will be made
with the surgeon prior to the surgery. It is also important to remember that not
every untethering operation leaves a hole in the dura which requires a graft,
and sometimes the tissues of the dura can just be closed by suturing them
together.
Q: What are the percentages of patients who are better after
surgery? Worse?
JRM: This is another very difficult question and would depend on
what kind of patients we are talking about. Certainly more complicated
operations and multiple re-untetherings make it more likely that the outcome
will be less favorable. Also, the more complicated the abnormality in terms of
the relationship of nerve roots to, for example, a large lipomeningocele, makes
it more difficult to achieve a satisfactory outcome. For an individual patient,
the physicians and surgeons responsible for care should be able to give an
opinion about the risks and benefits of surgery.
Q: Are problems like diastematomyelia hereditary? If this is not
hereditary, what is the cause?
JRM: For almost all of these syndromes, there is a very low
probability that someone else in the family will be affected. However, these
disorders must logically result from some combination of genes and the
environment of the developing spinal cord. The availability of antenatal
diagnosis, including ultrasound and now special sequences of MRI scanning that
create images of the developing fetus, give both the family and the surgeon an
opportunity to be prepared for the abnormalities which may occur.
Q: Are frequent bending and lifting something to be concerned about
if the cord is still tethered? If the cord is untethered, would frequent gentle
stretching and bending exercises keep the cord from retethering?
JRM: We actually received several questions pertaining to techniques
patients might utilize to avoid further injury to the cord. The retethering
process is unpredictable and poorly understood making it very difficult to
obtain data on whether a particular type of exercise or activity could affect
the outcome. Some patients, however, may develop pain while doing to specific
actions. My advice would be to consult with your neurosurgeon to try to
determine the exact cause of the pain. Some possible causes could be spinal
deformities, wear and tear damage to the joints in the spine, orthopedic
deformities in the extremities or to retethering of the cord itself. It is
always very difficult to know what a reasonable activity load may be but it is
quite likely that gentle and nonpainful stretching is good for the spine
including the untethered spinal cord. It is probably not damaging and may be
helpful whether or not it actually inhibits retethering.
Previous On-Line Lectures
Letter from John Shillito, M.D.
Potential Cost of Non-Invasive Telemetric
Monitoring in Patients with Shunted Hydrocephalus, by David Frim, M.D.,
Ph.D.
Neurosurgical Treatment of Spasticiy, by
Joseph R. Madsen, M.D.
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