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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
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| 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.
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| Fig 3: Depiction of stent across the neck of aneurysm. |
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| 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)
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| 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.
i University of Pittsburgh, Department of Neurological Surgery, “Center for Endovascular Therapy,” <http://www.neurosurgery.pitt.edu/endovascular/> (January 8, 2005).
ii Alan S. Boulos, et al., “Evolution of Neuroendovascular Intervention: A Review of Advancement in Device Technology,” Neurosurgery 54, no. 2 (2004): 438.
iii Aman B. Patel and David M. Johnson, “Endovascular Treatment of Neurovascular Disorders,” The Mount Sinai Journal of Medicine 71, no. 1 (2004): 32.
iv Aman B. Patel and David M. Johnson, “Endovascular Treatment of Neurovascular Disorders,” The Mount Sinai Journal of Medicine 71, no. 1 (2004): 33.
v Ibid.
vi Aman B. Patel and David M. Johnson, “Endovascular Treatment of Neurovascular Disorders,” The Mount Sinai Journal of Medicine 71, no. 1 (2004): 32-33.
vii Ibid, 33.
viii Alan S. Boulos, et al., “Evolution of Neuroendovascular Intervention: A Review of Advancement in Device Technology,” Neurosurgery 54, no. 2 (2004): 446.
ix C.L. Taylor, et al., “Complications of preoperative embolization of cerebral arteriovenous malformations,” Journal of Neurosurgery 100, no. 5 (May 2004): 809.
x A. Mahmood, et al., “Dural arteriovenous malformations of the skull base,” Neurological Research 25, no. 8 (2003): 860-864.
xi Alan S. Boulos, et al., “Evolution of Neuroendovascular Intervention: A Review of Advancement in Device Technology,” Neurosurgery 54, no. 2 (2004): 447.
xii “Rush Begins Use of Magnetic Guided Navigation System Designed for Safer, More Precise Access to the Brain and Heart,” <http://www.cinn.org/news/stereotaxispressrelease.html> (December 12, 2002).
xiii Ibid.
xiv Leigh Atkinson and Martin Wood, “Coil Embolization of Intracranial Aneurysms,” ANZ Journal of Surgery 73 (2003): 674.
xv Ibid, 674-675.
xvi “Alfried Krupp Krankenhaus: Study confirms good results of coil treatment for aneurysms,” Hospital Business Week via IncRx.com (February 15, 2004).
xvii Ibid.
xviii “Humanitarian Use Device: Neuroform Microdelivery Stent,” (January 20, 2005).
xix “Neurosurgeons testing cooling method to treat brain aneurysms,” Pain & Central Nervous System Week via NewsRx.com (July 12, 2004): 27.
xx Demetrius K. Lopes, MD, and L. Nelson Hopkins, MD, “New Paths in Endovascular Surgery,” CINN Report (Winter 2003): 2.
xxi “Aneurysm: Nonsurgical treatment may be most beneficial for older adults,” Medical Devices & Surgery Technology Week via NewsRx.com and NewsRx.net (January 25, 2004).
xxii Leigh Atkinson and Martin Wood, “Coil Embolization of Intracranial Aneurysms,” ANZ Journal of Surgery 73 (2003): 674.
xxiii Ibid.
xxiv George A. Petrossian, MD, FACC, and Wesley S. Moore, MD, FACS, “Carotid Artery Disease,” Heart Center Online, <http://www.heartcenteronline.com/myheartdr/common/artprn_rev.cfm?filename=&ARTID=457> (January 8, 2005).
xxv Ibid.
xxvi Alan S. Boulos, et al., “Evolution of Neuroendovascular Intervention: A Review of Advancement in Device Technology,” Neurosurgery 54, no. 2 (2004): 439.
xxvii Aman B. Patel and David M. Johnson, “Endovascular Treatment of Neurovascular Disorders,” The Mount Sinai Journal of Medicine 71, no. 1 (2004): 35.
xxviii George A. Petrossian, MD, FACC, and Wesley S. Moore, MD, FACS, “Carotid Artery Disease,” Heart Center Online, <http://www.heartcenteronline.com/myheartdr/common/artprn_rev.cfm?filename=&ARTID=457> (January 8, 2005).
xxix Alan S. Boulos, et al., “Evolution of Neuroendovascular Intervention: A Review of Advancement in Device Technology,” Neurosurgery 54, no. 2 (2004): 439.
xxx Ibid.
xxxi Alan S. Boulos, et al., “Evolution of Neuroendovascular Intervention: A Review of Advancement in Device Technology,” Neurosurgery 54, no. 2 (2004): 439.
xxxii Ibid, 439-440.
xxxiii “Boston Scientific EPI: A Carotid Stenting Trial for High-Risk Surgical Patients (BEACH Trial),” (January 20, 2005).
xxxiv Alan S. Boulos, et al., “Evolution of Neuroendovascular Intervention: A Review of Advancement in Device Technology,” Neurosurgery 54, no. 2 (2004): 440-441.
xxxv Ibid, 441.
xxxvi Ibid, 438.
xxxvii Alan S. Boulos, et al., “Evolution of Neuroendovascular Intervention: A Review of Advancement in Device Technology,” Neurosurgery 54, no. 2 (2004): 444-445.
xxxviii George A. Petrossian, MD, FACC, “Stroke,” Heart Center Online, http://www.heartcenteronline.com/myheartdr/common/artprn_rev.cfm?filename=&ARTID=614> (January 8, 2005).
xxxix Alan S. Boulos, et al., “Evolution of Neuroendovascular Intervention: A Review of Advancement in Device Technology,” Neurosurgery 54, no. 2 (2004): 438.
xl Petrossian GA: Stroke. Heart Center Online, http://www.heartcenteronline.com/myheartdr/common/artprn_rev.cfm?filename=&ARTID=614: January 8, 2005.
xli Alan S. Boulos, et al., “Evolution of Neuroendovascular Intervention: A Review of Advancement in Device Technology,” Neurosurgery 54, no. 2 (2004): 438.
xlii Aman B. Patel and David M. Johnson, “Endovascular Treatment of Neurovascular Disorders,” The Mount Sinai Journal of Medicine 71, no. 1 (2004): 38.
xliii Alan S. Boulos, et al., “Evolution of Neuroendovascular Intervention: A Review of Advancement in Device Technology,” Neurosurgery 54, no. 2 (2004): 441.
xliv Paul Jacobs, “Concentric Medical gets OK for blood clot device,” MercuryNews.com, <http://www.mercurynews.com> (August 17, 2004).
xlv Ibid.
xlvi “Critical Information for Clinical Decisions,” VasSol, Inc. (2004).
xlvii Ibid.