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- Saving brains
from the inside: endovascular neurosurgery for
the
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prevention of
stroke
Currents
6-27-01
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- John C. Chaloupka, M.D.
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- Highlights:
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Cerebral endovascular revascularization is
now rapidly emerging as a
selective therapeutic
modality for stroke prevention
Contemporary
endovascular techniques include the Guglielmi
Detachable Coil (GDC) for preventing
hemorrhagic stroke and
percutaneous transluminal
angioplasty (PTA) and stenting for
preventing
ischemic stroke
A group in UI Hospitals and
Clinics increasingly uses these
techniques with
a success rate ranging from 98.7% (for
extracranial
PTA and stenting) to 93% (for
intracranial PTA and stenting)
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History:
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Until the early 1990s, stroke preventive
strategies were limited to
anti-atherosclerotic medical
regimens or surgical interventions for
revascularization
of the cerebrovascular system. However, both
approaches produced unsatisfactory
results and presented
excessive risks of perioperative neurologic
morbidity and
mortality. That is why, during the 1980s,
neurointerventionalists started
experimenting with a variety
of endovascular methods for prevention of both
hemorrhagic and
occlusive cerebrovascular disease.
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- These
minimally invasive techniques are now rapidly
emerging as the
state-of-the-art therapeutic modality
for brain revascularization. Endovascular
surgery
minimizes the risks associated with
craniotomy, brain retraction, and
surgical vessel
manipulation as well as complications, such
as vessel perforation,
postoperative infections, or
epilepsy.
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Occluding intracranial aneurysms is the most
common problem in hemorrhagic
stroke prevention,
followed by repairing cranial arterio-venous
(AV) malformations
and dural AV fistulas. Ischemic
stroke prevention, on the other hand,
includes
revascularization of acute thrombotic or
thromboembolic arterial occlusions and
athero-occlusive
disease and eliminating vasospasm.
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- Most
of intracranial aneurysms remain asymptomatic
until they rupture. The
primary purpose of endovascular
surgery for ruptured aneurysms is to prevent
a fatal
rebleeding. The purpose of treating cerebral
thrombotic, embolic, or low-flow
disease is to minimize
the effects of incipient cerebral ischemia.
Thanks to a
well-developed collateral compensation,
cerebrovascular occlusion is not
synonymous with
cerebral infarction. The latter occurs when
cerebral ischemia is
prolonged and compensation becomes
inadequate. Therefore, in the treatment of
all these
cases time and precision are of the essence.
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- New
facts: The first devices used to occlude
intracranial aneurysms were balloon
catheters. Early
attempts centered on sealing off giant or
fusiform aneurysms, but
later, the application was used
to treat smaller aneurysms with the aim of
keeping
parent artery patency. Next, intravascular
platinum coils with various thrombogenic
attachments
were introduced to thrombose intracranial
lesions. However, the coils
proved to be uncontrollable
once expelled from the catheter. To overcome
this flaw,
an electrically detachable coil was developed
by Guglielmi (known as the Guglielmi
Detachable Coil or
GDC). GDC is radio-opaque and verysoft,
making it
adjustable under radiologic control and
adaptable to the size and shape ofthe
aneurysm. A small
positive electric current applied to it helps
a thrombus to form
inside the aneurysm. The current also
dissolves the delivery wire, allowing the
coil to
detach from the catheter and further serve as
a dense mesh that prevents the
thrombus from displacing
into the parent artery and the distal
vascular tree.
Currently, there are also attempts to use
injectable liquid polymers to fill aneurysms
instead of
coils.
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- The
endovascular treatment of cerebral
athero-occlusive disease includes
percutaneous
transluminal angioplasty (PTA) and stenting.
Angioplasty is the
technique of physical dilation of
arteries that have become stenosed.
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- PTA
is designed to maintain blood flow by
increasing the cross-sectional diameter
of arteries
narrowed by atheromatous plaques. It may also
favorably alter rheology,
thereby reducing thrombus
formation. Finally, PTA may in the long term
slow the
progression of plaques. PTA is performed
using a balloon catheter that is inserted
through a
peripheral artery or vein and guided under
radiologic control to the
occluded vessel.
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Stents are metallic "sleeves" that are
delivered using an angioplasty balloon. They
reconstruct
the vessel wall while excluding the lesion.
Stents have been used mostly
in extracranial arteries,
such as the carotids, but they are becoming
increasingly
used for intracranial arteries as well.
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Although so far clinical trials have
documented only the efficacy of the
conventional carotid
endarterectomy for preventing stroke in
properly selected
patients at risk, there is cumulating
evidence (including that from ongoing
clinical
trials) that endovascular techniques are
likely to become an important alternative
primary
therapeutic modality for stroke prevention.
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Practice: The group using extra- and
intracranial endovascular surgery for stroke
prevention
in UI Hospitals and Clinics has noted a
dramatic rise in caseload within
the past two years.
This is due to a combination of enhanced
technical capabilities
and refined technological
equipment as well as to the willingness to
consider
cerebral endovascular revascularization in
patients with poor alternative therapeutic
options.
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review of 90 consecutive extracranial PTA and
stenting cases shows a technical
success rate of 98.7%.
There have been no deaths or major strokes
and only two
minor strokes. These results have been
achieved without the use of distal protection
devices
designed to minimize downstream embolization.
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recent experience with 40 consecutive cases
of intracranial PTA and stenting has
also shown a high
overall technical success rate of 93%, with
one death and two
major perioperative strokes. One
angiographic restenosis has been detected in
a patient
undergoing intracranial PTA alone.
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from curtailing the importance of open
endarterectomy, cerebral endovascular
revascularization
is gaining momentum as a modality of choice
in patients with
high risk for serious perioperative
morbidity and mortality. These include
patients
with contralateral carotid occlusion, severe
coronary artery disease, chronic
obstructive pulmonary
disease, obesity, unstable neurologic status,
and recurrent
stenosis after carotid endarterectomy.
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neurointerventional group at UI Hospitals and
Clinics has been selected to
participate in several
cutting-edge clinical trials evaluating new
devices and
techniques for the treatment of both
hemorrhagic and ischemic stroke. These
include: 1) The
U.S. Onyx Aneurysm Trial (liquid polymer
obliteration of
aneurysms); 2) The U.S. Onyx AVM Trial
(liquid polymer embolization of
AVMs; 3) SHELTER trial
(carotid stenting); 4) SSYLVIA trial
(intracranial
stenting); and 5) RPM mechanic reperfusion
device for acute stroke.
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Referral service: Patients at risk of
hemorrhagic or ischemic stroke can be
referred
to John C. Chaloupka, M. D., by calling
UI
Consult at 1-800-322-8442.
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