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Intracranial arterial stenoses: current viewpoints, novel approaches, and surgical perspectives

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Abstract

Ten percent of all strokes occurring in the USA are caused by intracranial arterial stenosis (IAS). Symptomatic IAS carries one of the highest rates of recurrent stroke despite intensive medical therapy (25 % in high-risk groups). Clinical results for endovascular angioplasty and stenting have been disappointing. The objectives of this study were to review the contemporary understanding of symptomatic IAS and present potential alternative treatments to resolve factors not addressed by current therapies. We performed a literature review on IAS pathophysiology, natural history, and current treatment. We present an evaluation of the currently deficient aspects in its treatment and explore the role of alternative surgical approaches. There is a well-documented interrelation between hemodynamic and embolic factors in cerebral ischemia caused by IAS. Despite the effectiveness of medical therapy, hemodynamic factors are not addressed satisfactorily by medications alone. Collateral circulation and severity of stenosis are the strongest predictors of risk for stroke and death. Indirect revascularization techniques, such as encephaloduroarteriosynangiosis, offer an alternative treatment to enhance collateral circulation while minimizing risk of hemorrhage associated with hyperemia and endovascular manipulation, with promising results in preliminary studies on chronic cerebrovascular occlusive disease. Despite improvements in medical management for IAS, relevant aspects of its pathophysiology are not resolved by medical treatment alone, such as poor collateral circulation. Surgical indirect revascularization can improve collateral circulation and play a role in the treatment of this condition. Further formal evaluation of indirect revascularization for IAS is a logical and worthy step in the development of intracranial atherosclerosis treatment strategies.

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Acknowledgments

This study received funding from the American Heart Association Science Innovation Award (NRG) and the Ruth and Raymond Stotter Chair Endowment (NRG).

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Authors and Affiliations

  1. Department of Neurosurgery, David Geffen School of Medicine at UCLA, 10833 LeConte Ave., Rm 18-251 Semel, Los Angeles, CA, 90095-7039, USA

    Nestor R. Gonzalez & Joshua R. Dusick

  2. Department of Radiology, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA

    Nestor R. Gonzalez & Fernando Mayor

  3. UCLA Stroke Center, Los Angeles, CA, USA

    Nestor R. Gonzalez, David S. Liebeskind & Jeffrey Saver

  4. Department of Neurology, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA

    David S. Liebeskind & Jeffrey Saver

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  1. Nestor R. Gonzalez
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Comments

Jan-Karl Burkhardt, Zurich, Switzerland

In this review article entitled “Intracranial arterial stenoses: current viewpoints, novel approaches, and surgical perspectives”, Gonzalez et al. provide an overview of intracranial arterial stenosis and report about their experiences with encephaloduroarteriosynangiosis (EDAS) as an indirect revascularization technique. Despite the results of the Carotid Occlusion Surgery Study (COSS), which were not able to show a risk reduction of ischemic stroke in patients with symptomatic atherosclerotic internal carotid artery occlusion and hemodynamic cerebral ischemia after bypass surgery compared to medical therapy alone, surgical revascularization is still indicated in highly selected cases [1, 2]. Besides the optimization of direct revascularization surgery (bypass) to decrease the operative complication rate, which was higher than expected in the COSS study, and to ensure that the entire area of hypoperfused brain tissue has been adequately revascularized, indirect techniques such as EDAS can be useful to improve revascularization (e.g., by increasing collateral formation). However, this technique needs further investigation in patients with symptomatic atherosclerotic internal carotid artery occlusion to assess the benefit as an adjacent to direct revascularization surgery or to medical treatment only.

Refernces

(1) Powers WJ, Clarke WR, Grubb RL Jr, Videen TO, Adams HP Jr, Derdeyn CP; COSS Investigators: Extracranial–intracranial bypass surgery for stroke prevention in hemodynamic cerebral ischemia: the Carotid Occlusion Surgery Study randomized trial. JAMA 306:1983-92, 2011

(2) Amin-Hanjani S, Barker FG 2nd, Charbel FT, Connolly ES Jr, Morcos JJ, Thompson BG: EC-IC bypass for stroke—is this the end of the line or a bump in the road? Neurosurgery. 2012 71(3):557–561

William W. Ashley and Christopher M. Loftus, Chicago, USA

In the paper entitled “Intracranial arterial stenoses: current viewpoints, novel approaches, and surgical perspectives”, the authors offer a well-written and basic review of intracranial arterial stenosis (IAS). They discuss its etiology as well as the underlying pathophysiology. They pay special attention to the relationship of angiogenesis and collateral circulation to intracranial arterial stenosis and subsequent stroke. Finally, they discuss the current treatment of symptomatic intracranial arterial stenosis in the shadow of the recent publication of the Carotid Occlusion Surgery Study (COSS) [1] and the Stenting and Aggressive Medical Management for Prevention of Recurrent Stroke in Intracranial Stenosis (SAMMPRIS) [2] trial data. They suggest that encephaloduroarteriosynangiosis (EDAS) and other adjunctive indirect revascularization procedures may offer a safe and effective alternative to direct and endovascular techniques.

Gonzalez et al. did an excellent job of providing an overview of IAS. They correctly indicate the multifactorial nature of the process. They also highlight the importance of hemodynamic factors in the development of the disease. Unfortunately, we still do not have a reliable way to predict which patients will ultimately go on to become symptomatic. Indeed, it may be that they are many subsets of patients with important, but yet unknown hemodynamic, genetic, or other factors that predispose them to certain disease phenotypes. There has been some promising work on biomarkers related to IAS and ischemia, but our understanding of the cell and molecular biology that leads to symptomatic IAS is still in its infancy. However, our ability to study flow and hemodynamic alteration is advancing rapidly and, in our opinion, offers an excellent opportunity to study and understand IAS. Moreover, careful case-by-case hemodynamic analysis is our best hope to correctly select patients for revascularization procedures.

That being said, there is still a great deal that we do not know, and more than anything else, this submission asks us to continue searching for a way to help IAS patients. We agree with the underlying premise that symptomatic IAS is a serious problem and medical therapy alone has unacceptably high rates of recurrent stroke and associated morbidity and mortality. Therefore, alternatives to medical therapy alone must be defined. The review suggests that EDAS may be useful for the treatment of IAS based on a small retrospective pilot study by most of the same authors [3]. In this study, 13 patients underwent unilateral EDAS plus or minus burr holes for symptomatic unilateral stenosis. There were no serious complications, 10 out of 13 total patients had angiographic evidence of increased vascularity and/or direct anastomosis after EDAS, there were no strokes in the follow-up period, and all but two had durable resolution of symptoms by 3 months. These are encouraging results and are on par with data from some other groups who have used EDAS for the treatment of intracranial steno-occlusive disease that is not classically defined as moyamoya disease [4, 5] and better than that seen when used for complete intracranial arterial occlusion [5].

This calls into question our implicit assumptions about IAS itself. Intracranial steno-occlusive disease is difficult to divide into clean boxes. As mentioned, it is multifactorial and usually overlapping. Moyamoya disease is classically defined as bilateral, progressive, idiopathic steno-occlusive disease affecting basal intracranial arteries. Moyamoya phenomenon has a much broader definition and can include unilateral findings and finding that are associated with other pathologies including atherosclerotic disease [4, 6]. Indeed as the authors themselves point out, “in only three patients could a definitive etiology of intracranial atherosclerosis be determined” [3]. It is possible that the patients mentioned in the study by Dusick et al. did have a phenotype of moyamoya. Indeed, Hallemeier et al. suggest that moyamoya phenomenon in North American adults is quite different from the classic Asian phenotype, is often unilateral, and can present like many of the patients in the pilot study by Dusick et al. Therefore, we still may not really know whether EDAS is really useful for atherosclerotic disease. But it is still very exciting to think that a procedure like EDAS may hold some promise. In order to further delineate the underlying pathologic process and better inform possible treatments, it may be beneficial to utilize advanced imaging techniques such as direct evaluation of the blood vessel wall using high field strength MRI [7] in addition to perfusion studies, PET, or quantitative MRI.

This is a timely submission that in light of the “disappointing results” of the recent COSS and SAMMPRISS data, forces us to think carefully about intracranial steno-occlusive disease and how we decide who will benefit from the treatment. Based on the SAMMPRIS and COSS data, some could take the pessimistic and, in our opinion, premature view, that direct surgical and endovascular cerebral revascularization should not be offered as treatment for symptomatic intracranial atherosclerosis disease. SAMMPRIS and COSS were both well done studies that required a great deal of hard work by a great many. But the data must be interpreted with the underlying assumptions in mind. Multiple groups have opined on the meaning of both studies and cited many valid reasons why they are not definitive [8–10]. One concept that most will agree upon is that medical therapy is more efficacious than expected and we as practitioners have a much higher procedural standard to uphold if we hope to see any benefit from intervention for this difficult disease. Thus, instead of wholesale abandonment of direct bypass and stenting, we must re-evaluate and refine our patient selection techniques and improve our procedural outcomes. So we applaud the author’s efforts to offer an alternative efficacious means of bypass that potentially addresses some of the pathophysiologic downfalls of direct bypass and stenting, while at the same time having a more favorable complication profile. We agree that further study must be done to elucidate whether EDAS can actually be useful for patients with symptomatic intracranial atherosclerotic stenosis. This will require careful consideration of clinical, hemodynamic, and imaging characteristics in order to select the right patients. We along with others in the cerebrovascular community look forward to the challenge. We are hopeful that EDAS along with other tools including direct bypass and intracranial stenting will offer some hope for the unfortunate group of patients with IAS that fail modern medical therapy.

References

1. Powers, W.J., et al., Extracranial–intracranial bypass surgery for stroke prevention in hemodynamic cerebral ischemia: the Carotid Occlusion Surgery Study randomized trial. JAMA, 2011. 306(18): p. 1983-92.

2. Chimowitz, M.I., et al., Stenting versus aggressive medical therapy for intracranial arterial stenosis. N Engl J Med, 2011. 365(11): p. 993-1003.

3. Dusick, J.R., Liebeskind, D.S., Saver, J.L, Martin, N.A, Gonzalez, N.R. Unpublished data.

4. Hallemeier, C.L., et al., Clinical features and outcome in North American adults with moyamoya phenomenon. Stroke, 2006. 37(6): p. 1490-6.

5. Komotar, R.J., et al., The role of indirect extracranial–intracranial bypass in the treatment of symptomatic intracranial atheroocclusive disease. J Neurosurg, 2009. 110(5): p. 896-904.

6. Goyal, M.S., et al., Clinical features and outcome in North American adults with idiopathic basal arterial occlusive disease without moyamoya collaterals. Neurosurgery, 2010. 67(2): p. 278-85.

7. Ashley, W.W., Jr., et al., Moyamoya phenomenon secondary to intracranial atherosclerotic disease: diagnosis by 3 T magnetic resonance imaging. J Neuroimaging, 2009. 19(4): p. 381-4.

8. Amin-Hanjani, S., et al., Extracranial–intracranial bypass for stroke—is this the end of the line or a bump in the road? Neurosurgery, 2012. 71(3): p. 557-561.

9. Qureshi, A.I., Interpretation and implications of the prematurely terminated Stenting and Aggressive Medical Management for Preventing Recurrent Stroke in the Intracranial Stenosis (SAMMPRIS) trial. Neurosurgery, 2012. 70(1): p. E264-8.

10. Wong, G.K. and W.S. Poon, Time to reflect on surgery and neuro-intervention for intracranial atherosclerotic diseases. J Clin Neurosci, 2012. 19(2): p. 222-3.

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Gonzalez, N.R., Liebeskind, D.S., Dusick, J.R. et al. Intracranial arterial stenoses: current viewpoints, novel approaches, and surgical perspectives. Neurosurg Rev 36, 175–185 (2013). https://doi.org/10.1007/s10143-012-0432-z

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