Stroke is generally thought of in the medical community as the presence
of severe brain ischemia, which may lead to death of brain tissue. Ischemia
occurs when the brain, or an area of it, does not have enough oxygen
(blood flow) to supply the demand. If the blood flow to a given area
decreases low enough, infarction -- or death of tissue -- occurs, (i.e., a
stroke). Surgery can sometimes prevent a stroke in patients at risk, and
can also alleviate the symptoms of ischemia in an area of the brain before
infarction occurs.
The other type of disease that is sometimes thought of as stroke is the
occurrence of a brain hemorrhage.
When a blood vessel ruptures, bleeding may occur in the brain, or in the
space between the brain and skull. Brain injury may result, and the
situation can be life-threatening. Surgery may in some instances be
life-saving, or in other circumstances, prevent the occurrence of
additional hemorrhages.
Extracranial
Carotid Endarterectomy
Narrowing of the carotid artery in the neck is nearly always caused by
atherosclerosis, fatty deposition in the wall of an artery that may cause its
narrowing. Pieces of this plaque material may break off and flow downstream,
where blood flow may be disturbed, or clot may form on the surface and lead to
complete blockage of the artery. Less often, the artery may be narrowed due to
dissection, which can be spontaneous or due to trauma. The flow of blood
'dissects' into the wall of the artery, which narrows the channel available
for blood flow.
If a person has symptoms such as brief inability to speak or inability to
move one arm or hand, such episodes, may be termed Transient Ischemic Attacks,
or TIAs. They may herald an increased risk for stroke, and merit urgent
evaluation by a neurologist or neurosurgeon. In other instances, one might
experience a sudden transient loss of vision in one eye, often described as the
sensation of a curtain being pulled down in that eye. If the carotid arteries
are examined using ultrasound, and the narrowing is subsequently proven to be
greater than 50%, surgery is often helpful in preventing a stroke from
occurring.
Carotid endarterectomy involves
surgically exposing the carotid artery, temporarily clamping it, removing the
atherosclerotic material, and stitching the artery closed (Figure
1). Following removal of
the clamps, flow is restored. Sometimes, narrowing of the carotid is discovered
in the absence of symptoms. In certain circumstances, it is helpful to perform
endarterectomy for non-symptomatic narrowing.
Figure 1.
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a. Here, an angiogram demonstates significant
narrowing of the carotid artery |
b. An operative photo showing the carotid artery and
its branches dissected out. Incision at artery being extended with
scissors.
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c. Closure of the artery
following removal of the plaque
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d. Completion of the artery closure
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Intracranial
Cerebral Revascularization
In rare circumstances, one or both carotid arteries become 100% blocked, the
brain being fed variably by alternative 'collateral' pathways. In some
instances, the amount supplied is inadequate, and TIA's result. Very severe
cases may progress on to stroke. Typically this situation is managed by
long-term anticoagulation with Coumadin, in hopes that more collateral
circulation may develop in time. If a patient is refractory to this treatment,
he or she may benefit from cerebral revascularization via a surgery called Extracranial
to Intracranial (EC-IC) Bypass. This is optimally accomplished by dissecting
the superficial temporal artery (STA) from the scalp, and 'plugging it in'
to a brain vessel, usually a branch of the middle cerebral artery (MCA). These
grafts directly provide new blood flow to the ischemic area of brain, and may
reverse the symptoms that are occurring (Figure 2). They may also prevent stroke. The
latter point is somewhat controversial, in that a large study was done in the
early 1980's, assessing the surgery's ability to prevent stroke, the
conclusion of which was that the surgery did not prevent stroke. The
conclusion of this study led to Medicare and insurance companies no longer
providing reimbursement for this procedure. Hence, there are very few surgeons
today who know how to perform it. Recently, data have been published to indicate
a method of selecting out those patients who are most at risk for stroke. As a
result, efforts are under way to organize a newer study to evaluate the results
of this procedure for stroke prevention.
Sometimes, it is necessary to intentionally sacrifice, or occlude, a carotid
artery, usually in the case of otherwise inoperable giant brain aneurysms. Prior
to actually occluding the vessel, a temporary balloon occlusion test is
performed to assess the patient's response to losing a carotid artery. The
majority of the time, this is well tolerated, but occasionally, severe ischemia
results. If occlusion is not tolerated, it is necessary to perform EC-IC bypass
prior to carotid sacrifice.
As noted above, the usual method for revascularization is superficial
temporal to middle cerebral artery bypass (STA-MCA). On occasion, the situation
may mandate the use of a vein graft, which is harvested from elsewhere, usually
the leg, as in coronary bypass surgery.
Figure 2
a. Preoperative Brain SPECT scan showing markedly
reduce flow to the brains right hemisphere (arrow). |
b. Postoperative Brain SPECT scan showing
near-normalization of flow in the right hemisphere (arrow). |
c. Postoperative angiogram showing the bypass graft
(arrow)
delivering flow to the brain. |
|
Brain Parenchyma
Hypertension
Hemorrhage, or bleeding inside the cranium is frequently devastating and
often fatal. The most common cause of bleeding into the brain substance, or parenchyma,
is uncontrolled hypertension. Blood pressures in excess of 200 are
usually seen, and usually the patient is unable to move one side of the body.
Treatment is directed best at prevention. When a large clot is present, a
life-threatening situation exists which requires emergent removal of the blood (Figure
3).
Unfortunately, such surgery cannot reverse the damage that has already been
done, and severe deficits, such as paralysis on one side, likely will persist.
Figure 3
a. Brain CT scan showing a large
hematoma (blood clot) deep within the brain |
b. Postoperative CT scan showing removal of the
hematoma |
Vascular Malformations
Bleeding into the brain substance may also be caused by malformed blood
vessels, called vascular malformations. These may be high pressure, high
flow lesions called arteriovenous malformations (AVM's), or smaller, low
pressure ones called cavernous malformations. Surgery to remove the malformation
is preventative in nature, but the malformation may also be removed if a
life-threatening hemorrhage is present and surgery is required to remove the
blood clot (Figure 4). Surgery for removal of an AVM is often performed
in conjunction with embolization to reduce the blood inflow. Embolization
is performed at CNI by the Interventional Radiology Service.
Figure 4
a .CT scan demonstrating a large
hematoma
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 b. Preoperative angiogram showing
the AVM in the dark, round mass as the top.
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c. Postoperative CT scan showing
removal of the hematoma
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d. Postoperative angiogram
following removal of the AVM
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Subarachnoid Hemorrhage
Intracranial Aneurysms
Aneurysms are a common cause of intracranial bleeding. An aneurysm is a
balloon-like dilation or pouch which usually occurs at the branch point to an
artery. They enlarge until the wall becomes so thin that there is a hemorrhage
(Figure 5). The blood usually fill the grooves on the brain's surface.
This space is called the subarachnoid space. The bleeding continues until the
body's mechanisms for stopping the bleeding take effect, or until the pressure
inside the cranium reaches the blood pressure, and blood flow to the brain
ceases. A significant portion of the patients sustaining a subarachnoid
hemorrhage die immediately, and significant portion of those who make it to the
hospital will eventually die as well.
When possible, surgery is performed to prevent further re-bleeding episodes.
Surgery is the established standard for direct treatment of brain
aneurysms. The aneurysm is dissected out using microdissection
techniques, and a metal clip is placed across the aneurysm neck (Figure
5), so that no more blood flows into it. The aneurysms subsequently
shrivels up and scars down. The current standard clips are made from
titanium and are safe for use with MRI scanning machines. Even if
surgery is carried out without any complications, the patient is still
at risk for 14 days following the initial hemorrhage. The blood that
leaked out is very irritating to the major arteries supplying the
brain, and in approximately 35% of patients, these vessels narrow
down due to spasm. If the spasm is severe enough, stroke or death
may result. Vasospasm may be treated by a variety of techniques ranging
from fluid management to catheter-based angioplasty (Figure
6). The latter is the most state of the art treatment and is available
at the CNI. Learn
more about aneurysms.
Figure 5
Figure 6
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a. This patient suffered a subarachnoid hemorrhage;
the aneurysm was
treated by platinum coils.
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b. On day 5, spasm ensued, which resulted in
inability to speak or move
the right side of the body.
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c. Following angioplasty, most of these symptoms reversed.
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On rare occasions, hemorrage and ischemia may affect the spinal cord. Hemorrhage
usually results from a vascular malformation, such as an AVM or a Cavernous
Malformation. Such hemorrhagic events are usually heralded by the sudden onset
of weakness of both legs or all four extremities. Surgical principles are
similar to those applied to vascular malformations of the brain.
Ischemia involving the spinal cord may result from a vascular entity
called a Dural Arteriovenous Fistula. Symptoms typically include progressive
weakness and spasticity of the legs. With a fistula, an abnormal connection
develops in which high-pressure arterial flow connects into a vein, which
isn't accustomed to such high pressures. This abnormal pressure can actually
reduce blood flow to the area of the of the spinal cord that is otherwise
normally drained by that vein. Surgery for these entities is not generally
complex, and involves dividing the abnormal vein.
