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Arteriovenous
Malformations (AVMs)
An arteriovenous malformation (AVM)
is a tangle of abnormally connecting arteries and veins. An arteriovenous
fistula (AVF) is also a combination of vessels with abnormal connections.
These two entities are very similar differing only in the type of
connection between the artery and the vein.
As normal vessels course towards the region of brain that they supply,
they divide into smaller and smaller branches. By the time they reach
their destination, they have branched into many tiny vessels called
capillaries. AVMs have abnormal connections between arteries and veins,
with no capillaries between. The blood coursing through the abnormal
vessels of an AVM is under high pressure. Veins are not used to such
high pressure–they usually have the capillaries between them and the
arteries to buffer that high pressure. Therefore there is the risk
of rupture at this high pressure interface or the abnormality may
exert pressure against the adjacent brain, resulting in seizures.
A stroke can occur if blood that is supposed to supply a portion of
the brain instead gets diverted through the AVM.
AVM Treatment
AVM’s can be treated from outside the blood vessels using surgery
or radiation therapy. Alternatively the AVM may be treated from inside
the blood vessels using endovascular embolization. Sometimes doctors
use combinations of these three techniques.
A surgical approach requires brain surgery through an opening in the
skull through which the surgeon’s instruments can enter. The AVM is
removed, and any vessels supplying it are disconnected.The radiation
therapy mode is called "radiosurgery" which is confusiong since no
surgery is actually performed. Radiosurgery tightly focuses a beam
of radiation on the abnormal vessels and after a period varying between
six months and two years the vessels gradually close off and are replaced
with scar tissue. Radiosurgery is an option that is limited to AVM’s
which are small.
Endovascular techniques can also be used to treat an AVM without brain
surgery. The treatment is performed in the angiography suite with
a catheter (a long thin tube) similar to that used during the arteriogram.
Through the catheter, the AVM is blocked off (embolized) so that blood
no longer flows through it. A variety of different materials may be
used to close off the AVM, including types of biosafe glues and particles.
Endovascular embolization of an AVM can be performed to cure the AVM
by itself or before surgery to minimize blood loss, making the operation
safer and shorter. It can also be performed before radiosurgery to
make the AVM smaller and increase the chance that radiosurgery will
be successful. The endovascular treatment of AVM’s is a relatively
new procedure and requires specialized training. Most endovascular
therapists are neuroradiologists who have completed additional training–ranging
from one to three years–in endovascular techniques.
We should make sure you understand that multiple embolization procedures
may be necessary to completely block off the AVM, or to block off
as much as possible before surgery or radiosurgery. It is not unusual
for you to have 2,3 or more trips to the neuroradiologist as he or
she embolizes different areas of the abnormal connections between
vessels. This is to ensure your safety. In general there are fewer
abnormal connections with arteriovenous fistulas (AVFs) than arteriovenous
malformations (AVMs).
How to Prepare: A Checklist
If you are an outpatient, one of our staff will call you several days
before your procedure to review your preparations and answer any questions.
You may also call (410) 955-8525 at any time. If you are an inpatient,
one of our staff will visit you the night before your procedure.
Please notify us several days prior to your procedure if:
You have allergies to x-ray contrast ("dye") or iodine.
You have a history of asthma or kidney disease
You take insulin, oral hypoglycemics (for diabetes) such as glucophage,
or blood thinners such as Coumadin, Persantine or Aspirin.
You are, or suspect you are, pregnant.
Take your medications as usual, unless told not to do so by your physician.
Take liquids as desired up to the time of your procedure. Take no
solid food within eight hours of your procedure.
If you are to receive general anesthesia for your procedure you must
have no food or drink after midnight the night before your procedure.
If you are an outpatient and you are to receive general anesthesia,
you will be scheduled to come to Johns Hopkins within a 2-week period
prior to your procedure for a "pre-anesthesia’ physical. If you are
an inpatient, the anesthesiologist will visit you the evening before
your procedure.
Do not bring jewelry or other valuables with you.
If you are an outpatient, arrange for someone to drive you home after
the procedure.
What to bring:
Bring any existing CT, MRI, myelogram, and angiogram films and reports.
If you have had a prior arteriogram bring those films or arrange to
have them sent to us in advance of your test.
Bring information about existing conditions and medications.
Bring appropriate medical insurance materials.
What to Expect:
Prior to Your Procedure
When you arrive, you will be greeted by a member of our staff and
registered for your procedure. A physician will explain your procedure,
answer any questions, and have you sign a consent form. An intravenous
line will be started in your arm to give you fluids and medications
to relax you if you require them. You will be taken to the procedure
room, where you will lie on your back during your angiogram. Cushions
and pillows will be used to make you comfortable. The skin where the
catheter will be inserted, which is usually in the upper thigh-groin
region, will be cleansed, and you will be covered from the shoulders
down with a sterile drape.
During your Procedure
The neuroradiologist will give you local anesthetic in your groin
which may cause slight discomfort for a few seconds before going numb.
A catheter will be inserted through a small incision in the skin.
You will feel minimal pressure in the area. The catheter will be guided
into the vessels to be examined.
When the neuroradiologist has placed the catheter in the correct position,
contrast dye will be injected which may cause a warm, but not painful,
feeling for a few seconds. During this time, you will also hear an
x-ray machine taking pictures. It is important to remain still, without
breathing or swallowing, while the dye is injected and the pictures
are taken. A nurse will be with you at all times. Please tell us if
you become uncomfortable.
You will probably not feel the effects of the occlusion of the AVM
when it is embolized. We will be checking on you constantly to make
sure you are feeling OK and are not having any neurologic problems
during the procedures. You may be asked to perform simple tasks to
ensure that the procedure is safely performed.
After your Procedure
In general, diagnostic procedures require about two hours of time
to perform; therapeutic procedures typically require more. When your
procedure is completed, pressure will be applied to the incision site
for 10-20 minutes, after which a small bandage will be placed over
the incision. No stitches are required. You will then need to lie
on your back with your leg straight and still for four to six hours.
A meal will be provided during this time.
After this procedure, you will be admitted to the hospital. This is
so that we can monitor you and make sure that the proceudre was succesful
and that you will have no problems thereafter.
If you are already an inpatient, you will be returned to your room
for observation by your floor nurse.
The neuroradiologist will communicate the results of your examination
to your physician, who will discuss the results with you at an appropriate
time. The referring physicians often prefer that we refrain from discussing
the findings with the patients, particularly before they have been
notified.
After you Leave
You may resume your usual diet after the procedure. Fluid intake of
48-64 ounces during the next 24 hours is recommended as this aids
in x-ray dye elimination.
Do not exert yourself for 24 hours following the procedure, after
which normal activity may be resumed. If you are an outpatient, a
family member or friend should drive you home and stay with you during
the 24-hour period.
It is not unusual to have minor bruising around the incision, but
if you experience bleeding or swelling there, or develop a cold or
painful leg, contact us immediately.
We try to call our patients (outpatients) or visit them (inpatients)
the day after the procedure. Please contact us at any time if you
have concerns.
X-Rays
We are trained in the use of x-rays and every effort is taken to use
the minimum of radiation. The small amount of x-rays used during routine
neuroangiography will not be harmful to you. If you notice that the
staff wear leaded aprons, it is because they work with x-rays everyday
and their occupational exposure is high.
Additional Information
For additional
information on the web, we recommend you click on the link below to
visit the ACR and RSNA patient information site:
Billing
If you are a self-pay patient, a bill will be issued at time of service
and mailed to your home.
If you are covered by a commercial health insurance carried, please
bring your cards or proof of coverage should be brought with you the
day of your study. We will file your claim for you. If you are covered
by Blue Shield of Maryland Major Medical or Medicare Part B, we will
also file your claim for you. Please note that you will be billed
for any balance not covered by your plan. If you are covered by Maryland
Medical Assistance, we will verify your eligibility and bill them
directly. If you belong to a Health Maintenance Organization (HMO)
or Preferred Provider Organization (PPO) with which we have a contract,
you must bring the referral and authorization form for the procedure
to be covered.
If your visit is due to an accident (work-related, automobile, etc.),
you must provide us with an authorization from the guarantor of your
bill.
Note that separate bills are issued by the Johns Hopkins Hospital
(to cover facilities, equipment, and support personnel) and The Johns
Hopkins University School of Medicine (to cover the services of the
physician neuroradiologists). So expect to see two bills for your
study.
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