Key
Points
1. Only Non-ionic contrast can be
injected into the thecal sac. We use
Omnipaque. Injection of ionic contrast into the thecal sac can
result in death.
2. While
performing the procedure remain aware of the patient's condition. Vasovagal reactions are fairly common
with myelograms, especially in young muscular males (football player
types). By intervening early one can
avoid a potentially life‑threatening reaction. See the discussion later in this handout.
3. Proper
labeling of the vertebral bodies is a critical aspect of the myelographic
examination. Surgeons rely on correct
labeling and communication of the lesion location.
4. When
performing Cervical Myelograms, take great care when extending the patient's
neck. Prolonged extension or
over-extension of the neck in a patient with a high-grade cervical canal
stenosis can result in permanent cord damage, even quadriplegia. Obtain and review any previous imaging
studies prior to performing the procedure.
5. Avoid
passing a needle through an epidural abscess into the thecal sac. This could result in meningitis. This also applies to any abscess or infected
decubitus ulcer, etc.
6. During a
cervical myelogram via a cervical needle placement, avoid injecting contrast
directly into the cord by never injecting contrast unless there is good flow of
CSF out through the needle.
General
Myelography refers to the examination of the
contents of the thecal sac after administration of intrathecal radiographic
contrast. The examination is done with
both plain films and CT.
Keep in mind that you will be doing multiple
examinations during your Neuroradiology rotation; therefore, it is important to
limit your exposure to radiation during each examination. Stand away from the tube and limit your
fluoroscopy time.
Basic
Anatomy and Physiology
The total adult CSF volume is about 150 ml (50%
intracranial, 50% spinal).
About 500-750 ml of CSF is produced each day (0.4 ml/min, 20-30
ml/hr). Adult opening pressure is
normally 7-15 cm fluid, >18 abnormal (although young adult can be slightly
higher with normal <18-20).
According to Dr. Hodges: The AP diameter of the cord is 7 mm down to
C7, 6 mm from C7 to the conus, then 7 mm at the conus. The cord size can be considered abnormal if
it is over 8 mm or under 6 mm.
There are normally 7 cervical vertebral bodies, 12
thoracic vertebral bodies, 5 Lumbar vertebral bodies, the sacrum and the
coccyx. There are corresponding nerve
roots: 8 Cervical, 12 Thoracic, 5
Lumbar, 5 Sacral, and the coccygeal nerve.
The position of the tip of the conus at birth is
debated. By 3 months it is usually at
the normal adult level of mid L1 to mid L2.
It is considered abnormal if it is below the L2-L3 disk space level
(ref. Barkovitch).
Indications
for Myelography
This examination is usually performed to assess
for HNP or spinal stenosis.
Less often it is used to determine the level of spinal cord
compression from metastatic disease or trauma.
Myelography often yields better information about
the bony structures than does MRI.
Alternative Examinations
MRI of the spine or a noncontrast CT can also yield useful
information.
Steroid
Premedication Regimen
Patients with a history of reaction to iodinated
contrast should receive premedication with steroids and Benadryl
(diphenhydramine) prior to contrast administration. However, contrast reaction is extremely rare
following myelography. The usual
premedication regimen (Manual on Contrast Media, 4th Ed. ACR, 1998) is: prednisone
50 mg PO 13, 7, and 1 hour before contrast administration; Benadryl 50 mg PO
(or IM or IV) one hour before contrast administration. If Benadryl is given make sure someone else
is available to drive the patient home.
For patients who can not take oral medication, substitute
hydrocortisone 200 mg IV for each prednisone dose and give diphenhydramine
IV. A period of at least 6 hours between the onset of corticosteroid administration
and the injection of contrast medium is recommended, regardless of the route of
steroid administration.
H2 blockers can be used for patients with a history
of severe reaction; cimetidine (Tagamet) 300 mg
In emergency situations, intravenous medications
can be administered: hydrocortisone (Solu-Cortef) 200 mg IV stat and q 4 hour
until the examination is complete.
Benadryl 50 mg IV 1 hour before contrast administration. Premedication with Epinephrine can also be
considered, but caution is advised in patients with unstable angina, arrhythmia
or hypertension (Manual on Contrast Media, ACR). A period of at least 6 hours between the onset of corticosteroid administration
and the injection of contrast medium is recommended, regardless of the route of
steroid administration.
ref: Greenberger PA, et al. (Oral) J Allergy Clin Immunol 1991; 87:867-872 and (IV) J
Allergy Clin Immunol 1986; 77:630-634.
Manual on Contrast Media, 4th Edition, ACR monograph,
1998.
Contraindications
and Acceptable Lab Values
Lab
values
PT (nl 10-12) acceptable < 15.0
seconds
Platelets (nl 150,000-450,000)
(bleeding time nl for platelets >100,000,
Transfuse < 50,000)
Coagulation parameters should be within normal limits. Check PT and PTT (and platelets) if there is
a clinical condition that predisposes the patient to bleeding. It is preferable to cancel or delay the
examination if PT > 15.0. If
possible, heparin should be held for 4 hours prior to the procedure. It can be restarted 2 hours after the
procedure. Coumadin should be held
for 3-4 days, until PT is normal. If platelets are below 50,000 (some prefer
70,000), a platelet transfusion can be given prior to LP (this situation occurs
especially in patients in whom an LP is being performed for administration of
intrathecal chemotherapy). Transfusion
of one unit of platelets raises the platelet count by 10‑20,000. Check the platelet count before continuing
with the LP.
Creatinine
is usually not checked prior to the myelogram.
If the patient has very poor renal function you could time the myelogram
to precede dialysis, or perform an MRI.
If a normal healthy
outpatient arrives without recent laboratory results it may be possible to
continue the examination at the discretion of the staff. Ask the patient about history of renal
disease or bleeding abnormalities before proceeding.
Medications that lower
the seizure threshold should not be administered for 48 hours prior to or
following the procedure. The patient
should be informed during the consent procedure that their risk of seizure is
higher than if they were not taking the medication. This mostly applies to tricyclic
antidepressants. Check the PDR if
uncertain whether the medication lowers the seizure threshold. (Many of these medications have half-lives
well over 48 hours; however, usually we still hold the medication for 48
hours.)
Drugs that lower seizure
threshold
(not an exhaustive list)
(source: Neuroradiology,
The Requisites, R.I. Grossman, D.M. Yousem):
Phenothiazines
(chlorpromazine [Thorazine], prochlorperazine [Compazine], perphenazine
[Etrafon, Trilafon], thioridazine [Mellaril])
Antipsychotics
(thiothixene [Navane], haloperidol [Haldol], droperidol [Fentanyl])
Tricyclic antidepressants
(amitriptyline [Elavil], desipramine [Norparmin], imipramine [Tofranil],
nortryptyline [Pamelor], doxepin [Sinequan])
CNS stimulants
(methylphenidate [Ritalin], ephedrine, pseudoephedrine)
Monoamine oxidase
inhibitors (tranylcypromine [Parnate], procarbazine [Matulane])
Others (lithium,
reserpine, isoniazid)
If the patient has a
history of seizures or is taking seizure medications, there is no premedication
for seizures. Discuss with the referring
physician and the patient that there is a higher risk of the contrast inducing
a seizure than in a patient without a seizure history. The patient should continue to take their
usual seizure medications prior to the myelogram.
Caution must be
exercised in patients taking the oral antihyperglycemic agent Glucophage
(metformin) because of the risk of renal failure or lactic acidosis after
receiving iodinated contrast. The FDA
package insert states that Glucophage should be withheld temporarily in
patients undergoing radiological studies using intravenous iodinated contrast media. We apply this to intrathecal iodinated contrast media also.
The Manual on Contrast
Media, 4th Ed. by the ACR (1998) states that "metformin should be
discontinued before or at the time of the procedure, withheld for 48 hours
after the procedure, and be reinstated only after renal function has been
re-evaluated and found to be normal."
Be sure to call the patient's physician so that he/she can manage the
patient's diabetes while off Glucophage.
Call the patient's physician before the procedure to verify that the
proposed plan to manage the diabetes is acceptable and discuss with the
physician instructing the patient as to when to resume taking Glucophage.
Low Molecular Weight Heparin
(Fragmin, Lovenox, Normiflow, Orgaran) are a contraindication to LP or
Myelogram.
Of course, never pass a
needle through an epidural abscess into the thecal sac. If a patient has a suspected lumbar epidural
abscess, an MRI is usually the best means of evaluation. If a myelogram must be done, introduce the
contrast into the thecal sac using the cervical
approach.
A complete CSF Block is
a contraindication to collecting CSF below the block. Reduction in CSF volume and pressure below
the block can cause downward herniation of the cord. The risk versus benefit of the procedure must
be considered in each case individually.
A Complete CSF Block is
a also a contraindication to injecting contrast below the block (of course, it
is acceptable to inject contrast above the block). This is because the block prohibits
resorption of the intrathecal contrast by the arachnoid villi in the head and
leaves neurotoxic contrast in contact with the spinal cord and nerve roots. Resorption through the ependyma is only
minimal and will not suffice in this situation.
If a complete block is
suspected, one can inject two cc of contrast below the suspected level of the
block as a test. Run the contrast up
into the head to assess whether a block is present at any level. If no block is present, inject the remainder
of the contrast and continue with the study.
If a block is present, do not inject any more contrast. The two cc of contrast already injected
should be visible on the CT examination and can help define the lower extent of
the block.
If the patient has
immediate pain during the contrast injection it might be due to distention of
the thecal sac below an unsuspected block.
Stop injecting and investigate whether a block is present.
Other general
contraindications include medical conditions that might lead to
complications. For instance, a patient
with bacteremia from a tooth abscess should not undergo myelography because of
the risk of meningitis.
Possible Complications
The most common
complications are due to meningeal reactions, spinal headache, vomiting,
vertigo, and neck pain. This is partly
the result of CSF loss due to dural injury from the puncture. This complication is minimized by using a
small needle. It also helps to orient
the bevel of the needle parallel to the longitudinal fibers of the thecal sac
during puncture (to separate the fibers rather than cut them). The limiting factor for needle caliber is the
viscosity of the injected contrast material.
The typical headache
after puncture can be distinguished from migraine or other types of headache by
the increased severity in the upright position and the spontaneous improvement
in recumbency. It has its onset
immediately after puncture or within a few hours.
Other complications
include nerve root damage, meningitis, epidural abscess, contrast reaction, CSF
leak, or hemorrhage,
Unlikely complications
include damage to the spinal cord, such as due to a low conus or tethered cord
with a lumbar approach or direct cord damage in a cervical approach. Other complications include death or
paralysis from cord damage due to injection of contrast into the cord or
hemorrhage in the cord from needle damage.
If it is discovered
during the injection that a large fraction of the contrast has gone into the
subdural space it is usually best to discontinue the study and reschedule it
for two weeks later. This is because the
enlarged (contrast containing) subdural space fills the region of the canal
that previously contained subarachnoid space.
It is thus difficult to reposition the needle tip into the subarachnoid
space.
If a small subdural
injection is discovered early, it may be possible to reposition the needle and
continue with the study.
Post
Procedure Instructions
The routine post procedure orders are:
Strict bedrest for 4-8h with HOB elevated 30
degrees, at discretion of the physician, then bathroom privileges the rest of
the day.
Light activity for 24-48 h after discharge.
Force Fluids.
No phenothiazines, tricyclic antidepressants or Tigan
for 48 hours after study.
Also, the
patient should be told that if there are any signs of meningitis (severe
headache with stiff neck, fever) within 48 hours he or she should contact their doctor or go to the
emergency room.
Post Myelogram Headache
Tylenol, horizontal position, forced fluids, and
caffeine all help relieve the headache.
The headache can persist up to a week after the procedure. If headache persists over 24 hours after the
myelogram or if there is a fever or signs of meningitis the patient should
contact his referring clinician or go to the emergency room.
It may be necessary for
the patient to receive a blood patch to alleviate the headache. Blood patches are effective at stopping post
myelogram headaches anytime between 24 hours and several weeks after the
procedure. The first blood patch is
effective in 70% of patients, a second blood patch increases the effectiveness
to 95%. If a headache persists at
48 hours after the procedure a blood patch should be considered. In the case of a severe headache, a blood
patch should be considered at 24 hours.
This involves an injection of 10-15 cc of autologous blood into the
epidural space. The Neuroradiology
Service performs the blood patch procedure on our post‑myelogram
patients. See Dr. Wippold's monograph
about the blood patch procedure, included here as an Appendix. The headache usually stops immediately after
the injection of blood. This suggests
that the mechanism of headache is not simply CSF leak. The procedure is effective even if the
epidural blood injection is not at the same level as the original myelogram
needle puncture. (The Pain Service also
performs the blood patch procedure, 362-8840.)
Equipment
Spinal needles come in 3.5-, 4.5- and 6‑inch
lengths. The standard needle is 22- or
25-gauge 3.5 inch. The longer needles
are larger-gauge (20-gauge 4.5 cm; and 18-gauge 6 cm). The use of smaller gauge needles has been
shown to reduce the incidence of spinal headaches. The flow of CSF through a 25-gauge needle is
insufficient to allow for CSF collection.
If a CSF sample is to be obtained, use a 22 gauge or larger needle.
Before starting the procedure, estimate the
necessary length of needle. It is far
preferable to start with a 4.5-cm needle than to find out that you are slightly
short after the attempted placement of a 3.5-cm needle.
Table
Weight Limits
According to the Special Procedures Supervisor,
Roberta McQueen-Eads, the published table weight limits are:
Rooms 321 and 326 (Siemens Angio Rooms): 330
pounds.
Room 309 (Philips Myelo Room): 297 pounds (135
kg).
CT on 3rd floor:
400 pounds (according to Roberta).
CT Somatom Plus 4 on 2nd floor: 500 pounds (according to Roberta).
Iodinated Contrast
Nonionic
contrast must be used for the examination. Intrathecal
administration of Ionic iodinated
contrast can cause death.
We use Omnipaque (Iohexol). It comes in 20-ml vials with concentrations
of 180 mg I/ml and 300 mg I/ml. The
adult dose limit for myelography is 3 g total of iodine (i.e., 17 ml of 180 mg
I /ml; or 10 ml of 300 mg I/ml). Use 180
for lumbar myelograms and 300 for cervical, thoracic, or combined
myelograms. (Some prefer to use 180 for
cervical myelograms with a cervical approach).
Consult the contrast material package insert for pediatric dose limits.
Before drawing the contrast into the syringe, the
technologist should show you the bottle.
Verify that (1) non -ionic
contrast is being used (Omnipaque), (2)
the expiration date has not passed (the date will appear, for example, as 07 02
indicating July 2002), and (3) the desired concentration of contrast (180 or
300 mg I/ml) is being used.
Admonition
Procedures in neuroradiology are based on finesse,
not brute force. Plan what you want to
do, set it up, recheck it, then do it. Avoid
multiple passes with the myelography needle by knowing ahead of time what you
want to do and how to do it.
LUMBAR MYELOGRAPHY
Preliminary
steps
Before beginning, talk to the patient. Obtain a history and learn what information
is desired from the test. Explain the
risks, benefits, and alternatives to the patient. Obtain written informed consent. The post myelogram orders should be explained
to the patient.
Write a short note in the chart before the
procedure including: indication for examination, labs, allergies, documentation
of the consent, planned procedure.
Check the lab values. Check whether the referring clinician has any
special requests concerning the myelographic examination or the CSF analysis.
Obtain old MR, CT, plain films and myelograms and
reports. It is important to look at the
old films prior to starting the procedure.
Determine the level of the suspected pathology; usually you should avoid
placing the needle at this level.
Exclude tethered cord or low-lying conus. Count ribs from chest x-rays and old
myelograms.
Place the patient prone on the table. It is useful to have a pillow under the
abdomen producing a slight flexion of the L-spine. Using fluoroscopy, carefully verify the
number of ribs and the number of vertebrae.
Document with plain films.
Have everything needed for the procedure set up
before beginning. Have the contrast
drawn up and flushed through the long connection tube. The short connection tube is used for CSF
collection. The long connection tube
holds 1.9 cc and the short connection tube holds just over 1.0 cc.
Locate the desired entry point with fluoroscopy
and place an ink mark on the skin. Prep
and drape the patient. Position the
patient in true prone, such that the transverse processes project in the
midline between the pedicles on fluoroscopy.
Locate the desired level for needle placement. (See Figures 1 and 2 at the end of this
section.) The usual level is L2-3. Above this, at L1-2, there is a risk of
damaging the conus (which normally lies at L1-2 or above). Degenerative disease is usually below this
level, and the presence of a large disk herniation or bulge can make it
difficult to place the needle tip in the thecal sac. The thecal sac is also smaller at the lower
levels, especially if there is epidural lipomatosis. The normal lumbar lordosis makes the L2-3
spinous processes and inter laminar space relatively perpendicular to the table
for easier needle placement than at other levels.
Estimate the approximate depth of the thecal sac
(i.e., is it superficial in a thin patient or deep in a large patient?). Anesthetize the skin with lidocaine. Deep lidocaine may not be necessary, a single
pass of a 22- or 25-gauge spinal needle is less painful than multiple passes
with a 22-gauge lidocaine injection needle and lidocaine injection.
Lidocaine mixed with bicarbonate is less painful
than straight lidocaine. Use a mixture
of 10 cc of 1-% lidocaine and 1 cc of 8.4% sodium bicarbonate. (ref: Hospital Pharmacy, 31(10), p.
1275-1282, (1996).
The attending spine neuroradiologist must be
present for the surgical procedure portion of the examination, i.e. needle
placement and contrast injection. This
is because a procedure surgical code is used in billing in addition to the film
interpretation code.
The two most common approaches for lumbar needle
placement are midsagittal and parasagittal.
It is useful to be proficient at both approaches because in some
difficult cases one may work better than the other.
In the midsagittal approach the needle is
usually placed between the L2 and L3 spinous processes, through the
interspinous ligament. (See Figures 1
and 2 at the end of this section.) The
needle should be positioned during placement such that the fluoroscopy beam
looks "down the barrel." The
needle should appear to be a dense dot projected between the transverse
processes on AP fluoroscopy. Hold the
needle with two hands; one index finger should hold the stylet in place, the
other hand should be at the skin.
AP fluoroscopy should be used periodically to
verify the needle trajectory. It is
often not necessary to move the fluoroscopy unit back and forth, completely out
of the way; just reach under the unit to advance the needle (for large patients
this may not be possible). Insert the
needle to the estimated depth of the thecal sac. Check the depth on lateral fluoroscopy. Check for CSF return by tilting the table
slightly head up and removing the stylet.
Move the image intensifier out of the way to remove the stylet. Check for CSF return. (Note: It is very important that the head of the
table is tilted up so that the column of CSF rises above the hub of the needle
before withdrawing the stylet, otherwise there will be no CSF return. This might lead you to erroneously believe
that the needle tip is not in the thecal sac, leading to unnecessary
repositioning.) With a 25‑gauge
needle the CSF return might be minimal and/or slow.
The needle can be "steered" slightly by
using the bevel. The bevel side is
indicated by a raised mark on the hub.
By rotating the needle, the bevel can be used to deflect the needle away
from obstructions.
The advantage of the mid sagittal approach is that
it is less painful than the parasagittal approach because the ligament is not
innervated to the same degree as the paraspinal muscles.
The disadvantage of the midsagittal approach is
that in a severely degenerated back it may be difficult to place the needle
between the spinal processes. The space
between the processes may be diminished, and the ligament may be severely calcified. This, along with the normal caudally oriented
spinous process and interspinous space, makes it difficult to access the thecal
sac with a needle that is oriented perpendicular to the table. Do not negate the advantages of fluoroscopy
by trying to place the needle at an angle other than parallel to the
fluoroscopic x-ray beam.
The oblique parasagittal technique is
performed by placing the needle on either side of the spinous process. The side with the greatest interlaminar space
is chosen. The patient is
positioned with the knee slightly turned outward on the side of desired needle
placement. This rotates the spine a
minimal amount (about 10 degrees) to demonstrate the interlaminar space just to
the side of the spinous process. Proceed
as in the midsagittal needle placement, being sure to use the fluoroscopy beam
correctly by looking "down the barrel" of the needle and seeing that
it is directly superimposed on the desired target space.
The advantage of the oblique parasagittal
technique is that the needle is not forced through the interspinous
ligament. It need not negotiate a
narrowed obliquely oriented interspinous space.
The disadvantage of the oblique parasagittal
approach is that it may be more painful than the midsagittal approach because
the needle passes through muscle instead of through ligaments. However, if the needle can be placed more
quickly and with fewer passes, the overall patient discomfort is less than with
the other technique.
Figure 1.
An AP view of the lumbar spine showing the osseus structures. The needle is oriented parallel to the
fluoroscopy beam in a midsagittal approach.
The fluoroscopic beam also has caudal angulation.
Figure 2. A
lateral view of the lumbar spine showing the relationship between the osseus
structures, the needle and the image intensifier. The x-ray beam is parallel to the path of the
needle. The image intensifier is angled
to optimally demonstrate the space between the spinous processes and laminae of
L2 and L3.
Vasovagal
Reaction
Occasionally a patient may have a vasovagal
reaction during placement of the needle.
This occurs most often in large young physically fit men (football
player types). Be aware of the patient fidgeting and sweating. Stop the procedure, place the patient in
Trendelenburg position and place a cool wet towel on the back of his or her
neck and head before the reaction becomes severe. Assess their pulse rate and blood
pressure. Let the patient recover
for an extra few minutes after they seem to have recovered. Trendelenburg position and smelling salts are
useful in moderate reactions (vials of smelling salts are taped to the image
intensifier). A severe reaction
(hypotension, bradycardia) may require IV Atropine and rapidly infused IV
normal saline. The Atropine comes
in premeasured syringes containing 1 mg.
The usual Atropine dose is 0.8 - 1.0 mg IV slow push. It can be repeated in 3-5 minutes, up to 2 mg
total. But the key point is to notice
the early signs, attend to the patient and avoid a severe reaction. After the patient recovers from a vasovagal
reaction they usually will not have another during the remainder of the
procedure.
Once the needle is placed and there is CSF return,
gently spin the needle around 180 degrees (with the stylet in place). This clears the needle from the dura and
helps avoid subdural or epidural injections.
Starting October 20, 1997 we will collect CSF for
laboratory analysis only when it is requested by the referring clinician. If CSF is to be collected, collect at least 1
cc in each of the 3 test tubes in the order of the test-tube label (1, 2, then
3). The rate the CSF collects can be increased
by having the patient periodically cough or bear down. Slightly more than 1 ml of fluid fills
the short connection tube. Collect the
CSF in the collection tubing when filling test-tube 3 by holding it at a
downward slope and gently disconnecting the tube from the needle and allowing it
to drain into the test-tube by gravity and siphon action. Tightly close the tubes and give them to the
technologists for labeling. The
technologists will transport them to the laboratory. The samples are analyzed for: cell count and differential, VDRL, glucose,
and protein. Patients tend not to like
to have CSF drip onto their backs; try to avoid it.
Sometimes there is a request to collect a large
volume of CSF. Neurosurgeons suggest
that we do not collect more than 30 cc.
Removal of larger volumes tends to cause subdural hematomas.
Connect the contrast syringe. Note that if 20 ml are drawn up initially,
and 2 ml are flushed through the tube, there remains 18 ml contrast in the
syringe. Thus the maximum allowable dose
of 3 gm contrast can be administered without flushing through the contrast in
the connection tube. (Note that the
maximal dose of 17-cc contrast is seldom necessary, 13 to 14 cc are usually
sufficient.) The goal is to administer
sufficient contrast so that the thecal sac is completely filled below the level
of the midbody of L3 when the patient is upright.
The contrast is injected under fluoroscopic
observation to avoid subdural or epidural injections. The table should be tilted with the patient's
head slightly upward. Lateral
fluoroscopy should be used initially to clearly see the first puff of
contrast freely fall away from the
needle tip to form a dense horizontal line of contrast along the ventral side
of the canal. A subdural or epidural
injection can be identified by accumulation of contrast at the needle tip or in
the dorsal (non-dependent) part of the spinal canal.
After one or two tests puffs are injected, then a
steady slow injection can be performed.
During this time, periodic lateral (or AP) fluoroscopy shows
filling of the caudal portion of the sac, with no accumulation of contrast near
the needle tip. Fluoro periodically
throughout the injection to verify that the needle tip does not migrate and
cause a subdural or epidural injection.
If contrast starts to accumulate near the needle tip during the injection
it usually indicates that the injection has become subdural. Stop the injection and consult the staff
or fellow.
Usually 13 to 14 cc of intrathecal contrast are
sufficient. This dose reduces the rate
of complications relative to the highest allowable dose of 17 cc. If the patient has a patulous thecal sac the
highest allowable dose of 17 cc may be necessary. The tubing is then disconnected and the
stylet is replaced. The needle and
stylet are left in place (or withdrawn slightly so that the tip is in the soft
tissues of the back) during filming to document its location and to help
localize lumbar vertebral levels.
Digital plain film images are obtained. Make
sure that the entire extent of the very distal caudal thecal sac is filled with
contrast before imaging. This may
require standing the patient almost completely upright (at least 45 degrees of
table tilt should be done in all patients).
If there is a tight stenosis that impedes passage of the contrast into
the lower lumbar/sacral canal, stand the patient up and have him or her flex
and extend. This usually opens the
canal sufficiently to allow for some passage of contrast. It is very rare to have such a tight stenosis
that insufficient contrast passes for adequate CT evaluation, even if the plain
films do not show adequate contrast.
AP, lateral, shallow oblique and steep oblique
images are obtained for the lower L Spine.
(The shallow and steep obliques are obtained at about 15 degrees and 25
degrees off AP, respectively.) The
Tavaras View profiles the L5 and S1 nerve roots. Head of the bed is elevated 30 degrees so
that the contrast accumulates in the lower thecal sac. An image is obtained with the tube angled
30 degrees relative to the patient (so that it is perpendicular to the floor).
The patient is then positioned to move the
contrast column higher and the same images are obtained for the upper L
spine. The lower images should include the sacrum and the upper images should
include the lowest rib to provide unequivocal landmarks for localization of
levels (this is a good habit to adopt even though the needle is also in place
for localization.)
Supine and weight-bearing flexion and extension
lateral views are obtained.
Finally, a conus view is obtained with the patient
supine so that the contrast accumulates near the thoraco-lumbar
junction.
During the plain film examination note levels of
pathology so that these can be included in the CT examination. This is especially true for pathology that is
outside of the usual limits of the CT examination (i.e., low thoracic or
sacral).
A short note is left in the chart documenting the
procedure, and describing any preliminary fluoroscopic findings.
The patient is transferred off of the myelogram
table onto a gurney and transported to the CT scanner. While waiting for the CT scan, the patient
should remain basically in the prone position so that the contrast stays
dependent in the lumbar lordosis (unless he or she is unable to tolerate this
position). The patient is then turned
supine for the CT scan.
If there is a long delay before the CT scan (10
minutes or more), the contrast might settle too much in the spinal canal
causing layering. If the delay between
the myelogram and the CT is longer than 10 minutes, the CT technologist should
tell the patient to alternately roll gently and slowly toward one side, then
toward the other side, etc.
This mixes the contrast and helps avoid layering. (You can have the patient wait for the CT in
the prone position; this ensures that he or she will turn over at least once
into the supine position for the CT.
Also, in the prone position, the contrast collects in the lumbar
lordosis--where you want it--rather than pooling in the sacrum.)
The technologists should also check the scanogram
at the beginning of the CT scan. If the
contrast is seen layering in the lumbar or sacral regions, the patient should
be rolled from side to side or completely around to mix the contrast before
proceeding with the CT scan.
CT is performed.
For the "disk protocol" the images cover L1-S1 with 3-mm
slices. The disk protocol slices are
grouped in sets (L12, L23, L34, L45, L5S1), each parallel to the disk
space. For the "stenosis protocol"
the images also cover L1-S1 but 5-mm slices are used and the images are all parallel
and contiguous over the imaged region.
For suspected pathology outside of the usual levels, instruct the
technologists to obtain images at additional levels.
CT images are photographed at a "myelographic
window" between usual CT bone and soft tissue windows (W 2000/C 0). This window is optimal for viewing the
contrast in the thecal sac.
The films are hung on the myelogram board in the
spine reading room along with comparison old examinations. The examination must be read and dictated on
the day of the procedure since many patients will have surgery the following
morning. The films are left up on the
myelogram board after dictation until the following morning. The procedure and findings should be
documented in the myelogram book in the reading room.
The dictation must include as the last line of the
procedure section, "Dr. Smith, the attending neuroradiologist, was present
during the procedure."
The findings portion of the report is best
organized level by level, i.e. all of the findings at L12 are described, then
L23, etc.
At North Campus, Dr. Cho does his own
puncture and dictates his own procedure note.
The neuroradiologist performs the fluoroscopy during needle placement
and then interprets and dictates the findings of the examination.
Lumbar
Myelogram with Congenital Lumbar Anomaly
These patients should usually be evaluated by MRI
before the myelogram in order to delineate the exact nature of their
anomaly. Often a lumbar myelogram is
obtained by injecting the contrast in the cervical region and running it down
to the lumbar region. This approach
avoids placing the needle through a region of anomaly. However, many of these patients have
associated cervical anomalies such as low lying cerebellar tonsils. Before placing a needle into the cervical
region you must be sure that there is no accompanying cervical lesion. A cervical MRI is the best and most positive
proof. If you are sure that the
patient's particular lumbar anomaly is not associated with a cervical anomaly
you might proceed without an MRI.
Cervical
Approach for Lumbar Myelogram
Occasionally it is necessary to do a cervical
approach for lumbar myelogram. Perform
the puncture as described below. It is
usually best to use 300 mg I/ml contrast so that adequate opacification will be
obtained after the contrast dilutes on its way down to the lumbar region. Inject the contrast with the head of the bed
up and allow the contrast to flow into the lumbar region (and not into the
head).
Note that only Neuroradiology Fellows and Staff
are allowed to perform C1-2 punctures and injections.
CERVICAL MYELOGRAPHY
Cervical
Myelography--Lumbar Approach
The history, consent, and old films are as
described above.
Using the lumbar approach for cervical
myelography, the contrast is administered in the lumbar region and manipulated
under gravity to the cervical region.
The patient can be positioned either prone or in the lateral decubitus
position while the contrast flows to the cervical region.
Beware, spinal cord damage can result if a patient
with severe cervical canal stenosis is over extended. Look at previous imaging studies before
positioning the patient to assess for cervical spinal canal stenosis. If there is
severe stenosis consider either a cervical approach for introduction of
contrast or use the lateral decubitus position for running the contrast up from
a lumbar introduction. Note that a
severe stenosis will impede passage of the contrast so there is no need to
extend the neck to create a lordotic depression to trap the contrast.
Patient in Prone Position: Pillow supports are placed around the head to
gently extend the neck and produce a lordotic cervical curvature. The contrast will collect in this lordotic
depression rather than running into the head.
Access to the thecal sac is as was described above
for the lumbar myelogram. 10 cc of
300-mg I/ml contrast are administered.
During administration the table is tipped with the patient's head
slightly downward. Care is taken to
avoid too steep of an angle, which would send the contrast beyond the cervical
lordosis and into the head. However, the
angle must be steep enough to allow the contrast to flow over the normal
thoracic kyphosis. The contrast can be
observed either with lateral or AP fluoro.
First verify the subarachnoid injection in the lumber region, then move
to the cervical region to monitor the contrast accumulation. Proceed with imaging as below.
Patient in Lateral Decubitus Position: By having the spine horizontal, this position
avoids the problem of getting the contrast over the thoracic kyphosis without
having it flow into the head. This
method is most useful in patients with an exaggerated thoracic kyphosis and
least useful in patients with scoliosis.
Access the lumbar thecal sac.
With the table level, administer the contrast. Adjust the angle of the table to avoid having
the contrast flow into either the sacral or thoracic region.
Position the patient in the lateral decubitus
position facing away from you.
Have the patient turn his/her face toward the ceiling and tip their
upper ear toward the upper shoulder to create a cervical depression. Using LATERAL fluoro observe the contrast as
it flows cephalad while tilting the table.
Once the contrast is in the cervico-thoracic region have the patient
turn prone with his/her head extended.
Adjust the table tilt to maximize the contrast in the cervical region.
Images are obtained: AP, lateral, steep and
shallow obliques. A swimmer's view of
the cervical-thoracic junction is obtained.
The plain film images should be acquired expeditiously while the
contrast is well concentrated in the cervical region.
CT of the cervical spine is obtained with 4-mm
slices from the foramen magnum to C4, and 2-mm thick images from C4 to T1. Additional levels can be obtained if
necessary.
Cervical
Myelography--Cervical Approach
The cervical approach should be performed only by Neuroradiology Staff or
Fellows. Residents are encouraged to
observe.
The cervical approach shares the same risks and
complications as the lumbar approach. In
addition, there is also the risk of direct trauma to the cord by the
needle. Contraindications to the
procedure include chiari malformation with low-lying cerebellar tonsils or a
low course of the posterior inferior cerebellar artery (PICA). If the CSF cistern posterior to the cord at
C1-2 is too small for safe puncture, a lumbar approach should be used. If previous MR or myelograms are available
they should be studied to exclude the presence of these entities. When filling out the consent form, remember
to include the risks that are unique to cervical myelography.
Ankle braces or a body harness should be used to
avoid the patient slipping off the table.
There are two approaches for cervical puncture,
the horizontal needle approach and the vertical needle approach. In the horizontal needle approach the patient
is positioned prone on the table, whereas for the vertical needle approach the
patient is positioned in the lateral decubitus position. Both involve placement of the needle at the
C1-C2 level.
In the horizontal needle approach, the
patient is placed in the prone position with the neck positioned such that the
contrast introduced into the C1-C2 area will pool in the cervical region (i.e.
so that it will not run into the head or down into the thoracic spine). This does NOT usually require extending the
neck, the normal lordosis of the neck in neutral position usually suffices. The important aspect is to tilt the table so
that the cervical spine is overall horizontal (between C1 and C7) with the
lowest point in the mid‑cervical region.
Use of a head-extending device is usually NOT
necessary (and not desirable). When the
neck is extended the cord is moved into the dorsal spinal canal where the
needle will be placed. The extended neck
position also closes the C1-C2 interlamina space where the needle is to be
placed. Finally, extending the neck
accentuates stenosis; this could potentially injure the cord in a patient with
severe stenosis or a large disk herniation.
Care is taken to position the patient such that
horizontal fluoroscopy views the spine in a true lateral projection. Line up the right and left external auditory
canals in the head and the right and left sides of the arch of C1 in the
cervical spine.
The horizontal needle is placed between the
pedicles of C1 and C2 at the junction of the ventral 2/3 and the dorsal 1/3 of
the spinal canal. Lateral fluoroscopy is
used. The needle is positioned so
that a "down the barrel" view is projected directly over the target
point. Estimate the depth from skin to
thecal sac (the needle can be placed over the patient's neck for direct
estimation). Insert the needle. Check the depth of the needle tip by AP
fluoroscopy. A characteristic
"pop" is felt when entering the dura.
Do not rotate the needle to clear it from the dura, as is commonly done
in the lumbar region. If the needle
happens to be in the cord this maneuver would increase the damage.
Common mistakes include: Placing the needle too far posteriorly; this
can cause one to pass posterior to the thecal sac. Another common mistake is to not advance the
needle slightly after the dura is entered; this may lead to a mixed
epidural/subdural/subarachnoid injection because the needle does not completely
clear the dura.
Either 10 cc of 300 (or 17 cc of 180 contrast) can
be used. Verify the location of the
needle in the thecal sac by fluoroscopy and by ample CSF return before
injecting contrast. Do not inject contrast if there is any chance of the needle being in
the cord. The first injection should
be a small puff viewed under lateral fluoroscopy. The contrast should be seen to cascade down
away from the needle tip, over and around the cord, and into the ventral side
of the thecal sac. Epidural and subdural
injections are identified by contrast pooling around the tip of the
needle. During the injection, care is
taken to avoid contrast running into the head (which may cause a seizure). Periodically fluoroscopic observation is used
throughout the injection to verify that the needle tip does not migrate and
cause a subdural or epidural injection.
As contrast begins to accumulate in the cervical
region the patients usually experience a crampy pain in the neck, across the
back and down the arms. This is probably related to direct irritation from the
contrast. The patient will want to move
his/her neck to relieve the cramp. If
you are satisfied that the pain is due to this and not some other cause, tell
the patient that this is a common but transient effect. It usually lasts about 10-15 minutes. Advise that changing positions will not help
and that soon the pain will lessen on its own.
Ask the patient to remain still for the filming.
Filming is as described in the lumbar
approach/cervical myelogram section.
The plain film images should be acquired expeditiously while the
contrast is concentrated in the cervical region.
The vertical needle approach for cervical
myelography involves placement of the needle at C1-C2 under vertical
fluoroscopy. This approach is most
useful when horizontal beam fluoroscopy is not available, such as when using a
"GI" x-ray table.
The patient is positioned in the lateral position. The needle is again parallel to the
fluoroscopy beam, but both are vertical, rather than horizontal as above. The contrast can be injected with the patient
in the lateral position, then the patient is rolled prone with head extended
after the needle has been removed.
Alternately, the patient can be rolled prone with the needle in place,
then the contrast can be injected (care must be exercised to avoid cord damage
from the needle during patient repositioning).
The dictation must include as the last line of the
procedure section, "Dr. Smith, the attending neuroradiologist, was present
throughout the procedure".
THORACIC MYELOGRAPHY
Thoracic myelography is relatively rare compared
to lumbar and cervical myelography.
A critical aspect of the thoracic examination is
documentation of location.
Before beginning the examination, document the number of ribs
so that later the location of any lesions can be unambiguously determined by
counting ribs either from the top or the bottom.
Contrast is placed in the thecal sac, usually with
a lumbar approach. In the rare instance
of a complete spinal block in the thoracic region, it may be necessary to also
place contrast above the block by the cervical approach to delineate the
superior extent of the block.
The patient is then placed supine with the head
elevated on a pillow to allow the contrast to pool in the thoracic region.
Images are obtained. It is critical that each image allows
unambiguous determination of the rib levels.
If it is not possible to include either the top or bottom rib on the image,
it may be necessary to use a radiodense pointer to point to a particular rib in
the image.
The CT portion of the examination is usually done
with contiguous 5-mm-thick images from T1 through T12. If pathology is seen on the plane films or on
another examination, obtain 2-mm images over the area of pathology.
Total
Spine (not for AVM)
The CT is usually done as:
Routine Cervical
5 mm contiguous slices through the T spine
Stenosis L spine (i.e., also 5-mm contiguous
slices).
Total
Spine Myelogram to Assess for AVM
If possible, determine the anatomic level of
clinical concern, or at least an uppermost level of concern. Statistically, the most common location of a
spinal AVM is in the lower thoracic region.
However, they can occur anywhere in the thoracic region. They are distinctly rare in the cervical
region. If no clinical level can be
determined, concentrate the examination on the lower thoracic region.
Theory:
Speed is of the essence in the myelogram in order to keep the contrast
bolus together. Obtain wide field of
view AP and Lateral films only. Do not obtain obliques as one would for a
routine myelogram. Obtain Lateral views
of the lumbar/conus region with the patient both supine and prone so that the
contrast layers are dependent in both the ventral and dorsal canal. In order to obtain a lateral of the thoracic
spine with the patient supine it may be necessary to build a spacer cushion
between the table and the patient (Important: do this before the contrast is
administered). By the time the contrast
is in the thoracic region it should be mixed enough that both supine and prone
lateral views are not necessary.
Procedure:
Use a lumbar approach to administer the contrast (10 cc of 300). Immediately remove the needle completely so
that the patient is free to roll supine.
Do not let the contrast pool in the sacrum, try to keep it in the
mid and upper lumbar region. Obtain AP
and Lateral plain films of the lumbar/conus region. Turn the patient supine and obtain another
Lateral of the lumbar/conus region. Keep
the patient supine and manipulate the contrast into the thoracic region. Obtain AP and Lateral plain films of the
thoracic region. Tip the patient
slightly head down for views of the upper thoracic region, including a
swimmer's view. Then turn the patient
prone with neck extended while manipulating the contrast into the cervical
region. The contrast bolus might be too
diffuse by this time for good plain films of the cervical spine.
Send the patient to CT. Obtain CT scans from the foramen magnum to
the sacrum (5 mm thick through, 8 mm in cervical regions, contiguous).
Summary: Non-magnified images for AVM of Thoracic
spine:
Prone
1. AP/Lat upper lumbar/conus
Supine
1. Lat
upper lumbar/conus
2. AP/Lat
mid lumbar
3.
AP/Lat/Swimmer upper lumbar
Prone
AP/Lat cervical
Have the patient lie supine while waiting for the
CT so that the contrast pools in the thoracic region.
CT (Supine)
8 mm cervical, contiguous
5 mm thoracic/lumbar, contiguous
2 mm over areas of concern, contiguous
RELATED PROCEDURES
Lumbar
Puncture under Fluoroscopy
If an LP can not be performed by the clinicians,
the patient can be sent for LP under fluoroscopy. Before beginning, check whether the referring
clinician has special instructions for the CSF analysis so that it is collected
and handled in the proper manner. CSF is
obtained. If access is not possible in
the lumbar spine, a cervical approach may be necessary.
In order to ensure that the proper laboratory
tests are ordered on the CSF sample, the collected CSF is given to the
referring clinician for disposition.
LP for Meningitis:
It is a good idea to start with a 20-gauge needle. In frank meningitis the purulent CSF may be
too viscous to flow through a 22-gauge needle.
LP for Multiple Sclerosis: When collecting CSF to examine for the
diagnosis of MS (usually cell count and differential, total protein, gamma
globulin, and oligoclonal bands), a minimum
of 8 cc of CSF must be collected.
LP for cells:
CSF is often collected to diagnose cells in a malignancy. If there is a large intrathecal or
intramedullary mass, the removal of CSF below the mass might cause it to
herniate downward. Previous images are
helpful to assess for risk of herniation.
One might consider a C1-2 or cisterna magna tap if there is a great risk
of herniation of a spinal lesion from lumbar puncture.
The dictation needs to explicitly state the staff
member's name and that he or she was present for the procedure.