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46 JAAPA VOL.19, NO. 11 NOVEMBER 2006
Although aneurysms occurring anywhere in the body
can be problematic, ...
48 JAAPA VOL.19, NO. 11 NOVEMBER 2006
objective is to prevent aneurysm rupture, which can be
accomplished us...
coils after they are placed into the aneurysm. If the neck
is too wide, it may be difficult to prevent prolapse of the
52 JAAPA VOL.19, NO. 11 NOVEMBER 2006
introducer wire by electrolysis following discharge of a
small electri...
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  1. 1. 46 JAAPA VOL.19, NO. 11 NOVEMBER 2006 Although aneurysms occurring anywhere in the body can be problematic, aneurysms within the cere- brovasculature are especially problematic because the brain is the end organ. Subarachnoid hemorrhage (SAH) caused by rupture of an intracranial aneurysm occurs at a rate of 6 to 8 per 100,000 population,1 and aneurysms that rupture cause significant disability or mortality in up to 50% of affected patients.2 The effects of blood flow disruption within the brain vary according to the vascu- lar territory affected. Aneurysm size and location are important variables in that morbidity and mortality rates are higher when the aneurysm is larger or when it is located within the posterior circulation.3 Aneurysms arising within the intracranial circulation occur in the general population with an incidence of 0.2% to 8.1%.4-7 Men and women are affected almost equally.8 Most aneurysms are diagnosed when patients are 40 to 59 years old.9 Intracranial aneurysms are un- common in the pediatric population and rare in those younger than 5 years.10 The etiology is not well understood, but epidemiolog- ic studies have identified certain factors that may con- tribute both to incidence and to risk of rupture. Uncon- trolled hypertension and current cigarette smoking are associated with an increased risk of rupture.8 There appears to be a genetic predisposition as well, especial- ly in persons with two or more family members who have had an intracranial aneurysm.11 Diseases such as Ehlers-Danlos syndrome, Marfan syndrome, and polycystic kidney disease can increase the likelihood.12 Patients who have had one aneurysm have a 15% to 45% chance of having additional aneurysms.13 Treatment is aimed at removing the aneurysm while preserving blood flow in the parent vessel. The primary Bryan Walker works in the Section of Interventional Neuro- radiology, Georgetown University Hospital, Washington, DC, and has no relationships to disclose relating to the content of this arti- cle. John Deveikis works in the Section of Interventional Neuro- radiology, Medical University of South Carolina, Charleston, and is a consultant for Boston Scientific. Steve Wilson works in cardiac, thoracic, and vascular surgery at the Heart Center, Peninsula Regional Medical Center, Salisbury, Md, and is a member of the editorial board of JAAPA. THE SURGICAL PATIENTTHE SURGICAL PATIENT Steve Wilson, PA-C, DEPARTMENT EDITOR An endovascular approach to the treatment of intracranial aneurysms Bryan D. Walker, MHS, PA-C; John P. Deveikis, MD FIGURE 1 This cerebral angiogram in the anterior-posterior (AP) projection (left internal carotid artery injection) shows an aneurysm at the anterior communicating artery. In and around the OR FIGURE 2 A cerebral angiogram in the AP projection (vertebral artery injection) demonstrates an aneurysm at the summit of the basilar artery.
  2. 2. 48 JAAPA VOL.19, NO. 11 NOVEMBER 2006 objective is to prevent aneurysm rupture, which can be accomplished using a traditional neurosurgical approach (craniotomy followed by placement of a clip across the base of the aneurysm) or using an endovascular ap- proach (filling the aneurysm sac with metallic coils). This article discusses the endovascular treatment of intracra- nial aneurysms as an emerging option. Pathophysiology and diagnosis The structural composition of the arterial wall in ves- sels within the dura is different from that of vessels elsewhere in the body. Vessels within the dura lack an external elastic lamina, and the adventitia and media are thin. Congenital thinning may be present at vessel branch points. These structural differences render ves- sels within the dura at increased risk for aneurysm for- mation due to an altered hemodynamic state, including those resulting from hypertension, arteriovenous mal- formation, and polycystic kidney disease. Other risk fac- tors for aneurysms include smoking, IV drug use, dam- age caused by radiation therapy, atherosclerosis, trau- ma, and infection.2 Approximately 90% of aneurysms occur within the anterior (carotid) circulation; the remainder occur within the posterior (vertebrobasilar) circulation. In the anterior circulation, ruptured aneurysms are most commonly found at the anterior communicating artery (see Figure 1, page 46), then at the posterior communi- cating artery, the middle cerebral artery bifurcation, and the internal carotid artery bifurcation. In the pos- terior circulation, most aneurysms are seen at the basi- lar artery bifurcation (see Figure 2, page 46), then at the vertebrobasilar junction and the posterior-inferior cerebellar artery.14-16 The most common clinical manifestation of a rup- tured aneurysm is SAH; 70% to 80% of cases of non- traumatic SAH are due to a ruptured aneurysm.2,17 Patients may present with severe headache, neurologic deficits, or seizures. Emergent noncontrast CT of the head is usually ordered because this test has a high sen- sitivity (around 90%) for subarachnoid blood.13 Once SAH is diagnosed, the suspicion of intracranial aneurysm is high and further neuroimaging is done. Catheter cerebral angiography is the gold standard for the diagnostic assessment of aneurysmal SAH; it pro- vides a high degree of anatomic resolution and allows the angiographer to obtain the best angles and images to sort out the aneurysmal morphology. Noninvasive CT angiog- raphy (CTA) or magnetic resonance angiography (MRA) may be useful as well. CTA can easily be used in the hyperacute setting when surgery is urgently required and provides images comparable to those obtained with conventional angiography (see Figure 3). Endovascular treatment options Until a little more than 10 years ago, the only treatment option for an intracranial aneurysm was open neuro- surgery with placement of a clip on the aneurysm neck. With new interventional neuroradiology techniques, however, many aneurysms can now be treated using an endovascular approach. Digital fluoroscopy, micro- catheters, and coils are increasingly being used to embolize aneurysms. Morphology must be determined before an aneurysm is treated using an endovascular technique. Aneurysms are most commonly saccular, with a single, definable opening to the parent vessel, referred to as the neck of the aneurysm. The ratio of the top, or dome, of the aneurysm to the neck determines the stability of the The surgical patient FIGURE 3 A posteriorly projected aneurysm is seen using CT angiography with 3D reconstruction (A). The same aneurysm is seen on a cerebral angiogram (B). A B
  3. 3. coils after they are placed into the aneurysm. If the neck is too wide, it may be difficult to prevent prolapse of the coils into the parent artery. A soft balloon may be employed to serve as a temporary neck to hold coils in position during placement. Once the coils are properly positioned, the balloon is deflated and is removed when the procedure is completed. More recently, stents have been used to create a scaffold that maintains the coils positioned in the aneurysm and keeps the parent artery patent, even in cases of wide-necked aneurysms. After the morphology, size, location, and number of aneurysms are known, treatment is planned. In the angiography suite, the patient is placed in a supine position on the table, and the femoral artery area is exposed bilaterally. Biplane fluoroscopy equipment is mandatory because it allows data acquisition in both the posterior-anterior and lateral projections simultaneous- ly. Diagnostic angiography is routinely performed with local anesthesia and sedation. If the patient is unstable or unable to cooperate, general anesthesia may be employed. For endovascular procedures, general anes- thesia is most commonly used. The femoral artery is accessed using a modified Seldinger technique, and an arterial sheath is placed to aid in catheter placement and exchange. A number of diagnostic catheter shapes (Berenstein, Simmons, H1H [Cook], and Newton) are available, depending on vascu- lar anatomy, to aid in vessel selection. Guidewires are also used within the catheter to select vessels. The use of fluoroscopy aids the angiographer in determining the catheter or guidewire position. The catheter is moved up the femoral artery to the iliac artery and up the aorta to the arch, where the great vessels of the neck origi- nate. The side where the lesion is suspected to be is usu- ally selected first. Radiographic contrast is injected, multiple biplane radiographic views are obtained, and then the rest of the vessels are studied. The entire intracranial circulation must be examined to determine whether multiple aneurysms exist.18 Aneurysms in the posterior circulation are more diffi- cult to approach surgically; therefore, the tendency is to treat them by coiling.19 Those in the middle cerebral or posterior communicating territories are easier to access surgically and have usually been treated with open sur- gical clipping. Until recently, when experience with bal- loon-assisted or stent-assisted coil embolization had im- proved, aneurysms with wide necks tended to be treated surgically. Patients who are too unstable for craniotomy and microsurgical clipping are more likely to be able to tolerate the less invasive endovascular treatment. When endovascular treatment is chosen, various coils and delivery systems are available. In 1991, the Guglielmi detachable coil (GDC) system became avail- able, allowing safe, effective endovascular occlusion of aneurysms.20 The coils now come in a variety of gauges (0.010-0.015 inch), lengths (2-30 cm), shapes (helical, 2D, 3D), and compositions (bare platinum or with bio- active coatings). A 5 or 6 French guide catheter is first positioned at a stable area within the parent artery in the neck (the common or internal carotid artery or the vertebral artery). Under fluoroscopy, a microcatheter-microwire delivery system is introduced through the guide catheter; the tip of the microwire, and ultimately the catheter, is placed within the aneurysm. The coil is attached to a stainless steel introducer wire or to a thin hypotube, which runs the length of the microcatheter. The coil is introduced into the catheter and delivered into the aneurysm sac. When deployed, the soft platinum coil conforms to the shape of the aneurysm. Once in position, the coil is detached from an VOL.19, NO. 11 NOVEMBER 2006 JAAPA 51 The surgical patient FIGURE 4 In these four images, coils are delivered sequentially into an aneurysm in the anterior communicating artery until the aneurysm no longer fills with contrast. Aneurysms in the posterior circulation are more difficult to approach surgically and tend to be treated by coiling. A B C D
  4. 4. 52 JAAPA VOL.19, NO. 11 NOVEMBER 2006 introducer wire by electrolysis following discharge of a small electrical current through the introducer wire. Coils mounted on a hypotube are detached by injecting small quantities of fluid into the tube. Multiple coils are sequentially delivered into the aneurysm sac until the flow of blood into the aneurysm has ceased or until no more coils can be introduced (see Figure 4, page 51). Complications of diagnostic cerebral angiography and endovascular treatment include thromboembolic stroke, aneurysm rupture, bleeding or infection at the access site, and allergic reactions to the contrast agent. Overall, major complications from diagnostic cerebral angiography occur at a rate of 2%.21 Aneurysm rupture during embolization has been reported to occur in 2% to 5% of cases.22 To minimize the risk of thromboembolic complica- tions, patients are anticoagulated during the procedure and for 24 hours after. Those with SAH are kept in the neurosurgical ICU for continued monitoring and treat- ment. Patients with unruptured aneurysms often go home the day after the procedure. Follow-up care con- sists of clinic visits along with neuroimaging to monitor whether the aneurysm remains completely occluded. The usual protocol includes follow-up arteriography at 6 months and high-resolution MRA annually. Discussion Although early neurosurgical intervention was known to reduce overall mortality in patients with acutely rup- tured aneurysms,23 until recently, there had been no ran- domized prospective studies to ascertain the usefulness of endovascular coil treatment of an acutely ruptured aneurysm. The International Subarachnoid Aneurysm Trial (ISAT), which compared neurosurgical clipping ver- sus endovascular coiling of ruptured aneurysms, demon- strated encouraging results for the use of endovascular coil treatment, especially at 1 year.24 ISAT was a multicenter, prospective, randomized trial conducted at centers offering both neurosurgical and endovascular treatment. Patients were evaluated by both neurosurgical and endovascular specialists and were enrolled if patients and specialists agreed that an aneurysm could be treated by either means. Patients were then randomized into a surgical or endovascular arm for treatment. Follow-up evalua- tions occurred at 2 months and 1 year to determine the rates of rebleeding and clinical outcomes. This study showed that at 1 year, patients who received endovas- cular coil treatment for a ruptured aneurysm had fewer poor clinical outcomes (23.7% dead or disabled) than did those treated with surgical clipping (30.6% dead or disabled, P = .001). There was a trend toward more delayed rebleeding in the endovascular group, but it was not statistically significant. In summary, endovascular coiling is an evolving ther- apy that provides new, less invasive treatment options for patients with intracranial aneurysms. The decision to treat an aneurysm with coiling or surgical clipping should be made on a case-by-case basis, after careful review by the neurosurgical and interventional neuro- radiology teams, to maximize patient safety and ensure the best outcomes. ■■ REFERENCES 1. Linn FHH, Rinkel GJE, Algra A, van Gijn J. Incidence of subarachnoid hemorrhage. Role of region, year, and rate of computed tomography: a meta-analysis. Stroke. 1996;27:625-629. 2. Byrne J. Review article: endovascular treatments for intracranial aneurysms. Br J Radiol. 1996;69:891-899. 3. Chen PR, Frerichs K, Spetzler R. Current treatment options for unruptured intracra- nial aneurysms. Neurosurg Focus. 2004;17(5):E5. 4. Inagawa T, Hirano A. Autopsy study of unruptured incidental aneurysms. Surg Neurol. 1990;34:361-365. 5. McCormick WF, Acosta-Rua GJ. The size of intracranial saccular aneurysms: an autopsy study. J Neurosurg. 1970;33:422-427. 6. Du Boulay GH. Some observations on the natural history of intracranial aneurysms. Br J Radiol. 1965;38:721-757. 7. Nakagawa T, Hashi K. The incidence and treatment of asymptomatic, unruptured cerebral aneurysms. J Neurosurg. 1994;80:217-223. 8. Weir B. Unruptured intracranial aneurysms: a review. J Neurosurg. 2002;96:3-42. 9. Weir B, Disney L, Karrison T. Sizes of ruptured and unruptured aneurysms in relation to their sites and the ages of patients. J Neurosurg. 2002;96:64-70. 10. Proust F, Toussaint P, Garnieri J, et al. Pediatric cerebral aneurysms. J Neurosurg. 2001;94:733-739. 11. Kim DH, Van Ginhoven G, Milewicz DM. Incidence of familial intracranial aneurysms in 200 patients: comparison among Caucasian, African-American, and Hispanic pop- ulations. Neurosurgery. 2003;53:302-308. 12. da Costa LB, Gunnarsson T, Wallace MC. Unruptured intracranial aneurysms: natu- ral history and management decisions. Neurosurg Focus. 2004;17(5):E6. 13. Latchaw RE, Silva P, Falcone SF. The role of CT following aneurysmal rupture. Neuroimaging Clin N Am. 1997;7(4):693-708. 14. Lasner TM, Raps EC. Clinical evaluation and management of aneurysmal subarach- noid hemorrhage. Neuroimaging Clin N Am. 1997;7(4):669-678. 15. Kasner SE, Liu GT, Galetta SL. Neuro-ophthalmologic aspects of aneurysms. Neuro- imaging Clin N Am. 1997;7(4):679-692. 16. Johnson MH. Vascular emergencies of the head and neck. In: Kandarpa K, Aruny JE, eds. Handbook of Interventional Radiologic Procedures. 3rd ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2002. 17. Salcman M. Diagnosis and management of subarachnoid hemorrhage. In: Salcman M, ed. Neurologic Emergencies. 2nd ed. New York, NY: Raven Press; 1990:73-95. 18. Setton A, Davis AJ, Bose A, et al. Angiography of cerebral aneurysms. Neuroimaging Clin N Am. 1996;6(3):705-738. 19. Lempert TE, Malek AM, Halbach VV, et al. Endovascular treatment of ruptured pos- terior circulation cerebral aneurysms: clinical and angiographic outcomes. Stroke. 2000;31:100-110. 20. Guglielmi G, Vinuela F, Sepetka I, Macellari V. Electrothrombosis of saccular aneu- rysms via endovascular approach, I: electrochemical basis, technique, and experi- mental results. J Neurosurg. 1991;75:1-7. 21. Guglielmi G, Vinuela F, Sepetka I, Macellari V. Electrothrombosis of saccular aneu- rysms via endovascular approach, II: preliminary clinical experience. J Neurosurg. 1991;75:8-14. 22. Cooperative study between the ASNR, ASITN, and the SCVIR. Quality improvement guidelines for adult diagnostic neuroangiography. Am J Neuroradiol. 2000;21:146-150. 23. Kassell NF, Torner JC, Haley EC Jr, et al. The International Cooperative Study on the Timing of Aneurysm Surgery. Part 1: overall management results. J Neurosurg. 1990;73:18-36. 24. 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;360:1267-1274. The surgical patient ISAT showed that at 1 year, patients who received endovascular coil treatment for a ruptured aneurysm had fewer poor clinical outcomes.