Advancements in Endovascular Neurosurgery
A subspecialty bridging the fields of neurosurgery
and radiology, endovascular neurosurgery (a.k.a. interventional
neuroradiology) involves the management and treatment
of complex neurologic lesions using minimally invasive
techniques.(i) For patients suffering from the neurovascular
disorders of arteriovenous malformation, intracranial
aneurysm, carotid artery disease and acute ischemic
stroke, an endovascular neurosurgeon considers three
modes of potential treatment: conventional surgery,
endovascular surgery and radiosurgery. The treating
physician’s grasp of all three areas is becoming
more and more essential as new technologies blur the
lines between disciplines to provide safer, more effective
means of treatment.
Within the greater metropolitan Chicago area there
are two endovascular neurosurgeons and a handful of
interventional neuroradiologists, Demetrius Lopes, MD,
a neurosurgeon trained in all three modes of neurovascular
treatment previously described, is the director of the
Cerebrovascular Surgery program at Chicago Institute
of Neuroresearch and Neurosurgery (CINN), and an assistant
professor of neurosurgery and radiology at Rush Medical
College. Dr. Lopes is involved in many ongoing studies
to advance the diagnosis and treatment of neurovascular
diseases.
In the rapidly evolving field of endovascular neurosurgery,
the past two years have brought dramatic improvements
in device technology.(ii) Through prudent application,
Dr. Lopes and his team are playing an active role in
developing these technologies and incorporating them
into new methods of neurovascular treatment.
ARTERIOVENOUS MALFORMATION
 |
| Fig.
1: Guglielmi Detachable Coils (GDCs) |
Arteriovenous Malformation (AVM) is an exceedingly
complex disorder. It consists of a nidus of coiled and
tortuous vascular channels shunting blood from arterial
feeders to draining veins.(iii) Unlike aneurysm or stenosis,
which can occur and be cured at any given point in one’s
life, AVMs are developmental; they are part of the brain
from birth. As such, a neurosurgeon must treat or extricate
a part of the brain itself. Obliterating the vascular
nidus completely is the only way therapy can remove
the risk of hemorrhage.(iv) To carry out this delicate
task, the neurosurgeon must possess an expertise in
the latest techniques and have access to the most advanced
tools.
“AVM is so complex, all appropriate tools or approaches
can be applied, depending on the individual case,”
observes Dr. Lopes. “It’s the only disorder
that requires the neurosurgeon to have expertise in
all three areas of treatment (i.e., conventional microsurgery,
endovascular surgery and radiosurgery). The key is to
be able to use the technology wisely.”(v) A multidisciplinary
team must consider the anatomical, functional and dynamic
information of an AVM patient before formulating a strategic
treatment plan.(vi) This involves weighing the relative
risks and benefits of a conservative approach vs. surgery
vs. radiosurgery vs. embolization, or some combination
thereof.(vii) The practice of embolization has advanced
the treatment of AVM notably in recent years.(viii)
Embolization is an endovascular technique that consists
of placing a microcatheter inside the AVM and injecting
an embolic agent under x-ray guidance to occlude the
AVM.
Embolization may be an effective stand-alone treatment
or may be used as a precursor to conventional microsurgery
or radiosurgery. To date, the technique of preoperative
embolization has been proven capable of gradually reducing
flow to an AVM, reducing intraoperative blood loss,
and reducing operative time—but risks still do
abound.(ix) Because an AVM’s clinical course, treatment
and final outcome are subject to the AVM’s location,(x)
a multidisciplinary approach will help determine if
this practice is appropriate for a particular patient.
ANEURYSM
“We are having a great impact on the disease,”
reports Dr. Lopes. “We are improving aneurysm outcomes
by acquiring the latest technologies, such as magnetic-guided
neurosurgery, gaining unparalleled experience with those
technologies, and tracking clinical results through
databases that enable us to evaluate our performance.”
Dr. Lopes and his team are engaged in ongoing clinical
work to develop more and better aneurysm treatment options
at each stage of the disease. The methods derived from
such trials help to identify aneurysms faster and fix
them more effectively, without negatively impacting
quality of life.
Historically, the treatment of aneurysms has been almost
as dangerous as the disease itself. The outlook is much
more promising today, given a neurosurgeon’s ability
to weigh all available treatment options fully. As with
AVMs, treatment of aneurysm requires a multidisciplinary
approach. Both endovascular technique as well as conventional
microsurgery are used in treating aneurysms. Optimally,
a specialist is comfortable applying either approach
or jointly with the other.
For every improvement in imaging systems, aneurysm
treatment—and endovascular techniques as a whole—gets
safer. Among the most exciting recent developments is
a radically new navigational system in which magnets
are used to direct magnetized catheters precisely to
their anatomic target.xi Rush University Medical Center
has joined Washington University in St. Louis and the
University of Oklahoma in Oklahoma City as one of only
three centers in the country equipped with an interventional
device from Stereotaxis, named Telstar. Telstar substantially
reduces the need to open the skull surgically and disrupt
brain tissue in order to repair aneurysms and deliver
stroke therapies, resulting in more effective treatment,
reduced costs and swifter recovery times.
“Magnetically-guided neurosurgery enables us to
go after problems we couldn’t touch, even two years
ago,” says Lopes. As the principal investigator
of the CINN clinical study with Telstar, Lopes has reported
great success with the system thus far. He expects his
clinical research with the technology to lead beyond
coiling to repair weakened blood vessels with stents
(metallic tubes).(xii) But for the moment, coils still
serve as invaluable instruments.
Since Guglielmi introduced endovascular coiling for
intracranial aneurysms in 1991 [Guglielmi Detachable
Coils (GDCs) (Fig. 1)], coiling has presented a minimally
invasive, non-surgical treatment option that achieves
the dual treatment goals of aneurysm occlusion and parent
artery preservation.(xiii) Coil embolization, thoroughly
demonstrated to be effective, is now established as
first-line treatment for many patients with ruptured
intracranial aneurysms.(xiv) One of the largest studies
to date has recently confirmed the high success rate
and good safety record of coil occlusion therapy, citing
82 percent of its coil procedures devoid of complications
and 86.5 percent of them resulting in complete or near
complete occlusion.(xv) These numbers suggest that the
early results of coil treatment are at least as good
as those reported for open surgery.xvi And it’s
getting better all the time. Neurosurgeons have begun
using coils that are coated with a biologically active
material to enhance the healing process by creating
scar and connective tissue within the aneurysm. Endovascular
specialists are also using hydrocoils (coated with expanding
gel), which allow increased packing of cerebral aneurysms.
 |
| Fig
3: Depiction of stent across the neck of aneurysm. |
 |
| Fig
2: Depiction of stent and coil technique. |
For the relatively few cases of wide neck intracranial
aneurysm, the Neuroform™ Microdelivery Stent from
Smart Therapeutics, Inc., can make placement of coils
within the aneurysm sac safer (Figs. 2 & 3). It
is the only stent marketed in the United States for
the treatment of wide neck intracranial aneurysms and
has recently been granted a Humanitarian Use Designation
by the FDA. This designation recognizes the fact that
the device is used to treat a disorder that affects
fewer than 4,000 individuals in the United States per
year and for which no comparable device is available.
Dr. Lopes is the principal investigator in an ongoing
study and one of the most experienced physicians in
the country with this device.xvii
In those instances when coils and other minimally invasive
techniques are not plausible for aneurysm patients,
conventional surgery, or “clipping” to seal
the aneurysm off from the rest of the blood circulation,
may be the only option—but this risky procedure,
too, is getting safer. Rush Medical Center is one of
five centers around the country and the only one in
the Chicago area participating in the first phase of
a study for a new cooling method. The ChillerStrip System,
designed by Seacoast Technologies, Inc., circulates
fluid to disposable silicon “strips” which
cool an aneurysm’s surrounding brain tissue to
about 63 degrees F while surgery is being performed.
“The idea of cooling is to diminish the metabolic
demands of the brain,” explains Dr. Lopes. “By
reducing the metabolic demand, you’ve reduced the
need for blood.” This technique prevents what can
otherwise be irreversible or fatal swelling action.(xviii)
There is no single definitive answer for aneurysm treatment.
The current overall trend has been to consider endovascular
treatment first, reserving surgical therapy only for
aneurysms with unfavorable geometry or other clear surgical
indications, such as intraparenchymal hematoma.(xix)
Endovascular therapies may be especially appropriate
for elderly patients and for patients with medical conditions
that might increase the risks of surgery.(xx) Some of
the other determining factors of treatment include aneurysm
size, number, location, parent vessel characteristics
and patient preference.(xxi) Additionally, as aneurysm
treatment evolves, new weight is being given to considerations
of patient age, health and whether or not a prophylactic
treatment will enable the patient to enjoy the same
activities he or she enjoyed prior to diagnosis. “It
is no longer a question of survival, but more a question
of how to restore the patient’s quality of life
as soon as possible,” observes Dr. Lopes.
CAROTID ARTERY DISEASE
Treatment methods of carotid artery disease (a.k.a.
carotid artery stenosis, or carotid atherosclerosis)
are advancing quite rapidly. Neurosurgeons are working
through smaller incisions, using smaller—and smarter—devices
to widen the narrowed arteries. Because the breadth
of treatment options can be daunting, it is important
for patients to receive comprehensive advice from physicians
who can discuss each available treatment at length.
Recent advances have been remarkable but are not appropriate
for every patient.
“Three years ago, we would need to do open surgery
to treat carotid stenosis,” recalls Dr. Lopes.
“Now, we do angioplasty, using balloons to place
stents. This is an appealing, minimally invasive way
to take care of the problem.”(xxii) Officially
termed Carotid Angioplasty and Stenting (CAS)—otherwise
referred to as carotid artery stenting—this new
technique was approved by the FDA in 2004 for use on
certain patients.(xxiii) CAS has emerged as a viable
intervention for critical, medically refractory, symptomatic
stenoses. It provides a less-invasive alternative to
the procedures of endarterectomy and bypass—open
surgeries that may lead to complications in high-risk
patients.(xxiv)
Dr. Lopes is co-investigator in an ongoing study, titled
“Carotid Revascularization Endarterectomy vs. Stenting
Trial (CREST).” He and his team will assess the
relative effectiveness of each treatment option. CAS
may avoid some of the perioperative complications associated
with endarterectomy, including wound complications,
cranial nerve damage and the risks of general anesthesia.
It also results in significantly less hemodynamic ischemia
than endarterectomy, since there is minimal, if any,
carotid occlusion time.(xxv) Despite these advantages,
research has shown that CAS has roughly the same rate
of complications as endarterectomy. However, it may
be safer than surgery in high-risk patients.(xxvi) Additionally,
three recent technological advances show promise of
making the less invasive procedure safer and reducing
the rate of CAS-related periprocedural morbidity: 1)
embolic protection devices for preventing thromboembolic
complications; 2) carotid artery-specific self-expanding
stents; and 3) the reduction in size and increase in
flexibility of the crossing profile for these stents
in their constrained state.(xxvii)
The first and most significant among these advancements
has been the emergence of distal protection devices.
Most are still being investigated, including those in
a clinical trial at Rush University Medical Center,
but preliminary data support their routine use in all
carotid stenting procedures.(xxviii) “Distal protection
devices enable us to prevent plaques from flooding the
bloodstream during a stent procedure,” describes
Dr. Lopes. The incidence of these embolic plaques during
CAS is 80 to 90 percent. Distal protection devices use
filtration or occlusive methods to prevent the embolic
debris from causing complications or stroke. (xxix)
In studies, the devices have lead to a reduction in
the incidence of periprocedure-related neurological
events, and since their advent, a five- to nine-percent
incidence has become a zero- to two-percent incidence.(xxx)
These results are very encouraging. Further confirmation
of the efficacy of such devices is expected shortly
as a Boston Scientific-sponsored trial concludes the
investigational study of a carotid stent combined with
an embolic protection system. Dr. Lopes has served as
a principal investigator in the trial, titled “Boston
Scientific EPI: A Carotid Stenting Trial for High-Risk
Surgical Patients (BEACH Trial) and co-investigator
in the SECURITY trial and CAPTURE registry.”(xxxi)
The second improvement in CAS technology has been the
introduction self-expanding stents, specifically designed
for delivery in carotid vessels. These stents have provided
a more durable alternative to those used elsewhere in
the body, while reducing the incidence of bradycardia
and hypotension. Stents with tapering sizes are currently
being investigated. They are expected to conform better
to the native anatomy of the internal carotid artery,
thus preventing spasm or vessel injury. Also under investigation
are closed-cell nitinol stents, designed to prevent
the release of embolic debris during stent deployment.(xxxii)
The fabrication of smaller delivery devices has been
the third recent advance in CAS. The new smaller sheaths
allow for easier negotiation of the aortic arch and
can be placed routinely without wire placement across
the carotid bifurcation. Because arterial access is
possible with a smaller puncture, the new sheaths also
allow for improved hemostasis in conjunction with the
use of currently available closure devices. Alternative
access points, such as the radial or brachial artery,
are also possible with the new devices.(xxxiii)
In addition to these recent advances, the ongoing development
of drug-coated stents is gaining momentum as a means
to inhibit restenosis in the coronary circulation.(xxxiv)
Restenosis following stent placement was once a common
occurrence, but that may be a thing of the past. The
growing use of eluting substrates and coating materials
such as polytetrafluorethylene (PTFE), titanium-nitrade-oxide
(TiNOX), heparin, Rapamycin, Taxol and phosphorylcholine,(xxxv)
bodes well for the future of carotid artery disease
treatment.
ACUTE ISCHEMIC STROKE
Stroke is the third leading cause of death in the United
States and a leading cause of adult disability and institutionalization.xxxvi
Ischemic stroke, caused by an interrupted blood supply
to the brain, is one of the most common and devastating
neurological disorders,(xxxvii) accounting for 88 percent
of all strokes.(xxxviii) Fortunately, it is patients
within this majority population that stand to benefit
most from ongoing advancements in neuroendovascular
technology.(xxxix)
“Time makes all the difference,” says Dr.
Lopes of stroke treatment. Case in point: an intravenous
agent, tissue Plasminogen Activator (t-PA), has proven
to be a very effective endovascular thrombolytic therapy
for acute ischemic stroke, but the agent can only be
administered within a three-hour window from symptom
onset.(xl) Responses are seldom that quick. The alternative
to pharmacological recanalization is mechanical arterial
recanalization(xli)—an area of constant progression
but nevertheless still limited to a six-hour window.
Current clinical trials of promising new devices and
techniques could expand the window of opportunity to
eight hours.
Presently, investigations are underway to develop mechanical
methods of arterial recanalization by disruption or
retrieval of thrombus. Endovascular physicians are testing
the Concentric Merci Retriever—the first device
for removing blood clots from the brains of stroke victims.
Very similar to a plumber’s snake for household
blockages (but miniaturized and more sophisticated),
the Concentric Merci Retriever snags stroke-causing
clots inside large arteries of the brain and removes
them. In testing, endovascular neurosurgeons and interventional
neuroradiologists are using balloon angioplasty to block
the blood flow, so that when the clot is taken out,
it won’t be sent through the blood stream. The
device may treat as many as 300,000 of the 700,000 Americans
who have strokes each year.xlii It is particularly promising
for patients who reach the hospital too late for standard
therapy with clot-busting medications or for those who
cannot tolerate clot-busters.(xliii)
 |
| Fig.
4: NOVA software 3D capabilities provide 3D and
4D rotatable images to visualize stenosis along
with noninvasive quantitative measurement of blood
flow. |
Another new technology being used is designed to expedite
the diagnosis/treatment process. Traditionally, a patient
would have to be symptomatic before diagnosis or treatment
could take place; there has been no way of determining
the volume of blood flow in vessels outside the operating
room. This tragic limitation may soon be overcome through
VasSol, Inc.’s Non-invasive Optimal Vessel Analysis
(NOVA) system—the first and only system in the
world that non-invasively quantifies the volumetric
blood flow rate in vessels of the brain (Fig. 4). In
essence, it allows neurosurgeons to obtain pictures
and information about the physiology of a blood flow
problem, diagnose neurovascular disease and take appropriate
actions to prevent the onset of stroke.xliv
Designed to work with any state-of-the-art MRI, NOVA
incorporates interactive 3D images that provide a fully-rotatable,
360-degree view of vessels. Physicians can visually
inspect all angles of a vessel and then select a precise
point for calculation of the volumetric blood flow within
that vessel. The system is flexible enough to be used
for evaluation of entire vasculatures or for pinpointing
specific areas of concern within a vessel. Working with
MRI data, NOVA provides a previously unattainable level
of information, which can be used to diagnose neurovascular
disease and develop better courses of treatment. Because
of its predictive qualities and completely non-invasive
methods, NOVA might even prove a worthwhile component
of annual physical exams for high-risk patients.(lxv)
CONCLUSION
A breadth of new treatment options is available for
patients suffering from AVMs, intracranial aneurysms,
carotid artery disease and acute ischemic stroke. Embolization
of arteriovenous malformations is rapidly growing safer
and more effective as liquid embolic agents yield promising
results. Radically innovative techniques involving magnetically-controlled
navigation systems and thoroughly proven coils and stents
are taking the treatment of aneurysm to new levels of
effectiveness. Carotid artery disease is being treated
through smaller incisions with smarter devices using
advanced CAS techniques, while the risk of restenosis
is diminishing with the development of drug-coated stents.
Additionally, the majority of stroke victims now stand
to benefit from devices that may provide earlier diagnosis
and an expanded timeframe for treatment.
Endovascular neurosurgical techniques are making therapies
for neurovascular diseases more effective and recovery
times shorter. Their minimally-invasive nature also
helps to address growing quality-of-life concerns for
a population that is living longer. Leading programs
are developing and applying such therapies through a
coordinated, multidisciplinary approach involving neurosurgeons,
neurologists, interventional neuroradiologists, cardiologists,
neuro-anesthesiologists, nurses, and a full-service
rehabilitation team. “As neurosurgeons, we must
decide the best approach—the one that will solve
the problem and have minimal impact on a patient’s
quality of life,” reflects Dr. Lopes. “And
the only way to ensure that your patients get that kind
of care is to rely on a facility equipped with the latest
technology and a large, experienced team.”
A special thanks to Demetrius
Klee Lopes, M.D. for providing clinical commentary
and editing the preceding article.
|
