Update
on Interventional Neuroradiology |
to pdf >>
By
Amon
Y Liu, MD
Introduction
Interventional
neuroradiology--a relatively new medical subspecialty known also as
endovascular neurosurgery--treats cerebrovascular, head and neck,
and spinal disease by using minimally invasive techniques. Interventional
neuroradiology was originally developed in the 1980s by neuroradiologists
and neurosurgeons. Since that time, dramatic advances in interventional
neuroradiology have been made possible by similarly rapid advances
in medical technology, such as neuroimaging (particularly digital
subtraction cerebral angiography and angiographic road-mapping), and
development of revolutionary medical devices. Many medical conditions
which could not be treated effectively 15 years ago can now be treated
curatively using current endovascular techniques. Indeed, even within
the field of interventional neuroradiology, new technology and devices
introduced within the past five years have allowed interventional
neuroradiologists to increase the number of life-threatening cerebrovascular
diseases which can be treated effectively.
This
article provides a brief overview of the historical basis for interventional
neuroradiology, current treatment options for different types of cerebrovascular
disease, and anticipated future developments in the field. This article
also discusses current status and future plans for the Interventional
Neuroradiology program at Kaiser Permanente (KP) Medical Center in
Redwood City, California.
Historical
Basis of Interventional Neuroradiology
Diagnostic
Neuroradiology
Diagnostic
neuroradiology is a subspecialty of radiology. The first report
of cerebral angiography (visualization of the cerebral vascular anatomy)
in a living human subject, in 1927,1 described a small
surgical incision made in the neck to puncture the common carotid
artery, after which radiopaque contrast material was injected as a
bolus for serial filming of the cerebral arteries and veins. In the
ensuing decades, cerebral angiography advanced considerably in accuracy,
efficacy, and safety. Direct surgical incision was replaced by percutaneous
direct carotid puncture, a procedure which has subsequently been supplanted
by percutaneous transfemoral catheterization (ie, insertion of a catheter
through the common femoral artery after percutaneous needle puncture)
and use of safer radiopaque contrast materials for cerebral angiography.
In addition, modern mechanical devices for injecting contrast material,
advent of digital subtraction angiography, new techniques for obtaining
high-speed serial films, and manufacture of modern high-performance
catheters also have contributed to the evolution of cerebral angiography
as an imaging modality which is safe and effective when used by experienced
operators.
Concurrent
with these developments, noninvasive advanced technology such as ultrasound,
computed tomography (CT), and magnetic resonance imaging (MRI) have
sometimes allowed interventional neuroradiologists to make more accurate
diagnoses and to plan endovascular interventions without making a
skin incision to see inside the body. Further improvements in noninvasive
imaging equipment and powerful computer processors have led to new
techniques for visualizing the cerebral vasculature using CT or MRI.
These techniques--computed tomographic angiography (CTA) and magnetic
resonance angiography (MRA)--are now often used to screen patients
for suspected cerebrovascular disease. These techniques reduce (but
do not eliminate) the need for diagnostic cerebral angiography, which
currently has greatest sensitivity for detecting subtle abnormalities
or diseases of the small and distal cerebral vessels.
Interventional
Neuroradiology
Interventional
neuroradiology is a radiologic subspecialty which was introduced
in the 1980s to help neuroradiologists and neurosurgeons to find effective
techniques for treating patients for whom traditional treatments (ie,
open brain surgery) were neither possible nor feasible. Conditions
precluding traditional treatment included giant cerebral aneurysm,
surgically inaccessible aneurysm, large arteriovenous malformation,
clinically significant medical comorbidity, or a combination of these
conditions. Introduction of cerebral angiography provided an avenue
for achieving more effective treatment for patients with these conditions.
Through
the 1980s, neurointerventional techniques were considered largely
experimental and were done only for patients who had no other treatment
options. In the late 1980s and early 1990s, two key developments in
angiographic equipment--digital subtraction angiography and roadmap
fluoroscopic imaging--permitted dramatic growth of interventional
neuroradiology. Digital subtraction angiography initially had resolution
inferior to that of cut-film angiography but allowed more rapid decision
making during angiographic procedures by eliminating the need for
using time-consuming, conventional film processing after each angiographic
injection of contrast material. Roadmap fluoroscopic imaging has allowed
interventional neuroradiologists to obtain angiographic images of
a blood vessel, lesion (eg, cerebral aneurysm), or both by injecting
only a small amount of contrast medium and to maintain this angiographic
image on the fluoroscopic monitor while superimposing live fluoroscopic
(x-ray) images on the angiographic image. In essence, by giving interventional
neuroradiologists a "roadmap" of the blood vessel and lesion,
this imaging technique has enabled these specialists to treat the
lesion. For example, a "roadmap" can be used to guide a
catheter to the proper location within a blood vessel so that materials
can be deployed to treat a cerebral aneurysm. The "roadmap"
also enables interventional neuroradiologists to then inflate and
deploy a balloon within the aneurysm to occlude it. Indeed, interventional
neuroradiology would be impossible without the advent of roadmapping.
Equally
important for advancement of interventional neuroradiology were the
rapid technological improvements in each successive generation of
medical devices and materials. In general, therapeutic procedures
in interventional neuroradiology are done through a microcatheter
measuring between .013 and .021 inches in diameter. The microcatheter
is inserted coaxially through a larger catheter (the "guide"
catheter, measuring approximately 2 mm in diameter) placed in the
groin. Under fluoroscopic (x-ray) guidance, the microcatheter is threaded
through the blood vessels leading into the brain. Depending on the
disease process being treated, any of several devices or materials
may be deployed or injected through the microcatheter.
Despite
its strong roots in the field of radiology, interventional neuroradiology
has evolved into a distinct medical discipline that combines elements
of radiology and neurosurgery. Emergence of interventional neuroradiology
has marked a transition from the radiologist's traditional role as
a consultant: Interventional neuroradiologists serve not only as consultants
but as clinicians who assume an active role and responsibility in
treatment. As interventional neuroradiology continues to evolve, radiologists
as well as a growing number of neurosurgeons have entered the field.
The American Society of Interventional and Therapeutic Neuroradiology
was formed in 1992 as the governing body for this multidisciplinary
field.
Current Treatment
Options in Interventional Neuroradiology
The minimally
invasive procedures used by interventional neuroradiologists accomplish
a wide variety of treatments (some of which are described in this
article) designed to provide pain relief as well as to correct life-threatening
conditions. Such conditions include aneurysm (treated by inserting
platinum coils into the aneurysm bulge to promote clotting and to
prevent rupture), abnormal, enlarged cerebral arteries (treated by
injecting embolic material into a arteriovenous malformation to prevent
life-threatening hemorrhage), and stroke (treated either by delivering
"clot-busting" drugs directly to the site of blockage or
by using microdevices specifically designed to retrieve clots). As
alternatives to invasive surgery, these forms of therapy are often
advantageous because they can lower the risk to patients, shorten
hospital stays, and hasten recovery. Endovascular techniques also
allow treatment of many lesions which could not be treated with open
surgery.
Similarly,
interventional neuro-radiologists use endovascular and other percutaneous
techniques to treat some types of head and neck disease (for example,
embolic or sclerosing agents are injected to treat carotid blowout
syndrome, epistaxis, and facial hemangioma) and some types of spinal
disease (for example, a "glue" is injected to treat spinal
arteriovenous malformation, or cement is injected into a fractured
vertebra to treat pain caused by fracture).
Treatment
of Cerebral Aneurysms
Initially,
only aneurysms described as giant (> 2.5 cm) or otherwise inoperable
were treated using endovascular techniques. These aneurysms were treated
by inflating and detaching small silicone or latex balloons within
the aneurysm in the hope that filling the aneurysm would prevent its
rupture. Other aneurysms were treated, where possible, by using balloons
to deliberately occlude the blood vessel both proximal and distal
to the aneurysm.
The early
1990s brought a revolutionary advance to interventional neuroradiology:
the Guglielmi Detachable Coil, GDC (Boston Scientific, Natick, MA).
This device is an electrolytically detachable platinum coil which
can be delivered into a cerebral aneurysm to promote clotting within
the aneurysm. If satisfactory positioning of the coil cannot be achieved,
it can be withdrawn through the microcatheter. Currently, interventional
neuroradiologists planning treatment of aneurysms can choose from
among several types of FDA-approved coils: bare platinum coils, 2-
and 3-dimensional coils, aneurysm-conforming coils, bioactive coils,
and hydrogel-coated coils. These coils differ from one another in
performance characteristics, advantages, and disadvantages. When used
in the appropriate setting, these newer-generation coils are expected
to improve the stability of aneurysm coiling and thereby reduce the
need for repeat embolization.
The International
Subarachnoid Aneurysm Trial (ISAT)2 was designed to compare
the efficacy of aneurysm coiling versus open surgery in patients with
ruptured aneurysms. In 2002, investigators showed that patients who
were treated with coil embolization had improved outcomes compared
with patients who received open surgery.2
The next
revolutionary advance in endovascular treatment of cerebral aneurysms
came in 2003 with the introduction of the first stent approved by
the FDA for intracranial use. The Neuroform stent (Boston Scientific,
Natick, MA) facilitates treatment of wide-necked cerebral aneurysms
by bridging the neck of the aneurysm with a very thin meshwork which
prevents coil loops from prolapsing into the parent vessel and thereby
reduces the risk of a treatment-related stroke.
Treatment
of Cerebral Vasospasm
Interventional
neuroradiologists are also frequently called upon to treat cerebral
vasospasm, one of the devastating sequelae of aneurysmal subarachnoid
hemorrhage. Endovascular treatment of vasospasm may include use of
a microcatheter for intraarterial injection of vasodilating agents,
or balloon angioplasty of the intracranial vessels.
Treatment
of Cerebral Arteriovenous Malformations and Dural Arteriovenous Fistulae
These
types of vascular malformations can often cause debilitating symptoms
such as headaches or pulsatile tinnitus ("ringing or buzzing
in the ears") and can cause life-threatening intracranial hemorrhage.
Depending on the type of arteriovenous vascular malformation involved,
interventional neuroradiologists can very effectively treat these
lesions by injecting embolic agents such as polyvinyl alcohol (PVA)
and n-butyl cyanoacrylate (colloquially known as "glue"
and approved by the FDA in 2003) into arteries supplying the lesions.
In August 2005, the FDA approved Onyx (Micro Therapeutics, Irvine,
CA), a nonadhesive liquid embolic system composed of ethylvinyl alcohol
dissolved in dimethyl sulfoxide, for preoperative and radiosurgical
embolization of arteriovenous malformations. Other types of vascular
malformation can be treated using platinum coils placed through a
transvenous approach.
Treatment
of Intracranial and Extracranial Atherosclerosis
Increasingly,
interventional neuroradiologists are also treating these conditions
by using endovascular techniques, such as balloon angioplasty, stenting,
or both techniques. In patients who have symptomatic intracranial
atherosclerosis and who have suboptimal results of medical management
using antiplatelet agents or anticoagulants, stroke is highly likely
to develop shortly after this medical treatment;3,4 in
such cases, use of intracranial angioplasty, stenting, or a combination
of these techniques can make the disease less debilitating by improving
cerebral perfusion, by reducing the risk of thrombotic/embolic events,
or by both actions. The FDA has recently approved the first intracranial
stent, the Wingspan (Boston Scientific, Natick, MA), for use in atherosclerotic
disease, further raising the prospects for improved outcomes in affected
patients. Stenting of the extracranial carotid and vertebral arteries
has also advanced greatly. Carotid endarterectomy done by an experienced
surgeon remains a highly effective method of treating symptomatic
carotid stenosis, and most interventional neuroradiologists reserve
stenting for patients who are poor candidates for carotid endarterectomy.
(In these patients, the procedure is precluded by recurrent postendarterectomy
stenosis, radiation-induced stenosis contralateral carotid occlusion,
high-cervical stenosis, or clinically significant medical comorbidity).
However, multicenter randomized clinical trials, such as the Carotid
Revascularization Endarterectomy vs Stenting Trial (CREST),5
are well underway to determine whether carotid stenting done by experienced
operators is superior, equivalent, or inferior to endarterectomy for
treating carotid stenosis. Early results of this study have been encouraging
for stenting.
Vertebroplasty
In many cases, painful spinal compression fracture (osteoporotic or
traumatic), isolated vertebral bone metastasis, and vertebral hemangioma
can be treated effectively with vertebroplasty when the pain is not
relieved by analgesic medications. In such cases, a large spinal needle
is guided percutaneously into the fractured bone under x-ray guidance,
and a bone cement mixture is then carefully injected into the bone
to treat the fracture. In approximately 90% of appropriately selected
patients, the pain is either partially or completely relieved after
completion of this procedure.6 Many patients who receive
the procedure can safely eliminate or substantially reduce their use
of pain medication.
Future Developments
in Interventional Neuroradiology
The rapid
pace of technological innovation in interventional neuroradiology
makes this a very exciting field. Although we cannot precisely predict
what new devices may become available in the next five years, we can
certainly expect continued improvement in successive generations of
the coils and stents used for treating aneurysms. The Onyx liquid
embolic system (Micro Therapeutics, Irvine, CA) has also been used
successfully in clinical trials to treat selected cerebral aneurysms,7,8
and the manufacturer is expected to seek FDA approval for this indication
within the next two to three years. This embolic material may ultimately
be used in conjunction with coils or may in some cases replace use
of coils for aneurysm treatment.
In August
2004, endovascular treatment of acute ischemic stroke was advanced
substantially by FDA approval of the Merci Retriever device (Concentric
Medical, Mountain View, CA). The device is designed to restore flow
to the brain by retrieving embolic material (or blood clot) within
an occluded cerebral vessel. Nonetheless, the device is only approximately
50% effective in appropriately selected patients.9 Further
improvement in this and other similar devices is anticipated.
Continuing
improvement in imaging technology is also expected to enhance the
capabilities of interventional neuroradiologists. Angiographic equipment
improvements in image resolution, 3-D imaging, and imaging of soft
tissue all will help interventional neuroradiologists to make more
effective treatment decisions.
The Interventional
Neuroradiology Program at the KP Redwood City Medical Center
The Interventional
Neuroradiology program at the KP Redwood City Medical Center is led
by Amon Y Liu, MD; Gwinette Cowan, RN (Manager, Interventional Services);
and Beverly Land, RN (Interventional Neuroradiology Nurse Coordinator)
and includes a team of six angiography technologists and five staff
nurses. In September 2005, the team was joined by a second neurointerventionalist,
Sean P Cullen, MD.
The goals
of the Interventional Neuroradiology program at the KP Redwood City
Medical Center are
-
to extend the range of cerebrovascular and head and neck diseases
that can be effectively treated;
-
to improve rates of morbidity and mortality associated with treating
cerebrovascular and head and neck disease; and
-
to improve continuity of care and to reduce treatment delays in
the KP Northern California Region.
As the
regional service center for the neurosciences, the KP Redwood City
Medical Center has been able to form this cohesive team, which uses
a multidisciplinary approach to treating patients diagnosed with neurological
disease. With regard to patients with cerebrovascular disease in particular,
specialists in interventional neuroradiology, neurosurgery, and neurology-critical
care work closely with each patient to determine the best course of
treatment and management. At present, the Interventional Neuroradiology
service can provide all FDA-approved treatments that do not require
participation in clinical trials (except treatments for acute ischemic
stroke, which are treated on a case-by-case basis). Participation
in selected clinical trials is considered if a potential benefit to
a patient can be established. The service expects to offer complete
coverage for acute ischemic stroke upon certification by the American
Stroke Association as a comprehensive stroke center.
References
- Lowis
GW, Minagar A. The neglected research of Egas Moniz of internal
carotid artery (ICA) occlusion. J Hist Neurosci 2003 Sep;12(3):286-91.
- Molyneux
A, Kerr R, Stratton I, et al; International Subarachnoid Aneurysm
Trial (ISAT) Collaborative Group. International Subarachnoid Aneurysm
Trial (ISAT) of neurosurgical clipping versus endovascular coiling
in 2143 patients with ruptured intracranial aneurysms: a randomized
trial. Lancet 2002 Oct 26;360(9342):1267-74.
- Hass
WK, Easton JD, Adams HP Jr, et al. A randomized trial comparing
ticlopidine hydrochloride with aspirin for the prevention of stroke
in high-risk patients. Ticlopidine Aspirin Stroke Study Group. N
Engl J Med 1989 Aug 24;321(8):501-7.
- Thijs
VN, Albers GW. Symptomatic intracranial atherosclerosis: outcome
of patients who fail antithrombotic therapy. Neurology 2000 Aug
22;55(4):490-7.
- Hobson
RW 2nd, Brott T, Ferguson R, et al. CREST: carotid revascularization
endarterectomy versus stent trial. Cardiovasc Surg 1997 Oct;5(5):457-8.
- Hacein-Bey
L, Baisden JL, Lemke DM, Wong SJ, Ulmer JL, Cusick JF. Treating
osteoporotic and neoplastic vertebral compression fractures with
vertebroplasty and kyphoplasty. J Palliat Med 2005 Oct;8(5):931-8.
- Song
DL, Leng B, Zhou LF, Gu YX, Chen XC. Onyx in treatment of large
and giant cerebral aneurysms and arteriovenous malformations. Chin
Med J (Engl) 2004 Dec;117(12):1869-72.
- Molyneux
AJ, Cekirge S, Saatci I, Gal G. Cerebral Aneurysm Multicenter European
Onyx (CAMEO) trial: results of a prospective observational study
in 20 European centers. AJNR Am J Neuroradiol 2004 Jan;25(1):39-51.
- Smith
WS, Sung G, Starkman S, et al; MERCI Trial Investigators. Safety
and efficacy of mechanical embolectomy in acute ischemic stroke:
results of the MERCI trial. Stroke 2005 Jul;36(7):1432-8. Epub 2005
Jun 16.
Suggested
Reading
-
Nelson PK, Kricheff II, editors. Neuroimaging Clin N Am 1996 Aug;6(3)
[entire issue].
-
Rosenwasser RH, editor. Neurosurg Clin N Am 2000 Jan;11(1) [entire
issue].
