Extracranial-Intracranial Bypass and the Versatile Vertebral Artery

Accepted Manuscript EC-IC Bypass and the Versatile Vertebral Artery Peter Nakaji, MD Evgenii Belykh PII:

S1878-8750(14)00455-0

DOI:

10.1016/j.wneu.2014.04.071

Reference:

WNEU 2351

To appear in:

World Neurosurgery

Received Date: 28 March 2014 Accepted Date: 30 April 2014

Please cite this article as: Nakaji P, Belykh E, EC-IC Bypass and the Versatile Vertebral Artery, World Neurosurgery (2014), doi: 10.1016/j.wneu.2014.04.071. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT Nakaji & Belykh 1

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EC-IC Bypass and the Versatile Vertebral Artery

Evgenii Belykh2

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Division of Neurological Surgery

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Peter Nakaji, MD1

Division of Neurological Research Barrow Neurological Institute

St. Joseph’s Hospital and Medical Center

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Phoenix, Arizona

Correspondence: Peter Nakaji, MD

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c/o Neuroscience Publications; Barrow Neurological Institute St. Joseph’s Hospital and Medical Center

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350 W. Thomas Road; Phoenix, AZ 85013 Tel.: (602) 406.3593; Fax: (602) 406.4104 E-mail: [email protected]

ACCEPTED MANUSCRIPT Nakaji & Belykh 2 For an operation whose death knell we constantly seem to be hearing, extracranialintracranial bypass procedures have a remarkable vitality. Naturally, it is the indication of this procedure for low-flow bypass in anterior circulation ischemia that has suffered, but it is not so

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for other applications, such as high-flow replacement for patients with tumors, aneurysms, and vertebrobasilar disease. In these latter arenas, a great deal of ingenuity has been applied to

conceive an impressive variety of donor-recipient combinations. With practice, good outcomes

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have been obtained by many surgeons in these endeavors, including our group at Barrow Neurological Institute (1,2).

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In this issue, Yang et al. provide us with an interesting and useful account of their outcomes and technique of bypass using the V2 and V3 segments of the vertebral artery. Key points of their preoperative workup and the indications for microanastomosis on the vertebral arteries are presented and discussed. In general, this series consists of two types of patients.

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Yang et al.’s first group includes 6 patients with ischemia in the posterior circulation in whom blood flow was borrowed and redirected from the carotid circulation into the vertebral artery using a short-segment vascular interposition autograft, as well as 2 patients with carotid

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territory ischemia, in whom the middle cerebral artery blood flow was augmented with flow from the vertebral circulation. This highly select group of patients presented with transient

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ischemic attacks, and they mostly started out with excellent modified Rankin Scale grades and had bypasses performed for flow augmentation in a prophylactic fashion. The second group in this series is composed of 10 patients with aneurysms of the vertebrobasilar arteries. Their aneurysms were trapped with distal flow replacement by arterial microanastomosis into the second segment of the posterior cerebral artery (PCA) (7 cases) or V4 segment (2 cases), and by posterior inferior cerebellar artery (PICA) to V2/V3 bypass (1 case).

ACCEPTED MANUSCRIPT Nakaji & Belykh 3 The aim of these treatments was to redirect blood flow and facilitate aneurysm thrombosis. Despite the 100% anastomosis patency rate in this subgroup, there was one death and some morbidity among other patients, which reflect the complexity of intervening in this kind of

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pathology. Patients with these kinds of complex aneurysms are rare enough and different enough to require creativity, a broad range of bypass skills, and considerable judgment for treatment. And, they will never be testable in a traditional controlled randomized trial environment.

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Whether high-flow bypasses as presented in these cases were the best option, or whether a lowflow bypass might have sufficed in some of these cases is unanswerable. The patients generally

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did well in the face of challenging pathology, so we know high-flow bypasses are a reasonable option.

Yang et al.’s series is also useful because it reminds us of the utility of the extracranial vertebral artery for bypass. Because the vertebral artery lies in the neck and spine and is very

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accessible endovascularly, many cerebrovascular neurosurgeons do not spend time on its open surgical anatomy. We encounter it from time to time in the V1 segment for vertebral-carotid transposition for vertebral origin stenosis; in the V2 segment, when injured due to trauma or

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during anterior cervical discectomy or corpectomy; and in the V3 segment, when injury occurs from trauma or C1-2 spine surgery. The presence of two vertebral arteries, which often makes it

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so tempting to choose endovascular sacrifice as a first option when one artery is injured, also makes it attractive as a bypass donor or recipient. Temporarily occluding one vertebral artery or even diverting it entirely is possible, making it a good high-flow donor. The choice of the bypass strategy and donor vessel should naturally be based on the individual vascular anatomy of the patient. Alternative donors for the upper basilar circulation include distal branches of the external carotid artery (superficial temporal artery or occipital

ACCEPTED MANUSCRIPT Nakaji & Belykh 4 artery) to perform anastomosis with the P2 segment of the PCA or with the superior cerebellar artery (SCA) (1). The basilar artery itself, bristling with abundant tiny, but critical, perforating arteries that provide important blood supply for the brainstem has proven unattractive for direct

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bypass. As always, the basic principles of bypass should be considered: (1) Preserve vessels where possible. (2) Perform the fewest number of anastomoses. (3) Choose the easiest bypass. (4) Where possible, prefer the shortest bypass.

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Kalani et al. retrospectively reviewed data in our institution collected between 1993 and 2011 and revealed 11 patients with giant fusiform and complex aneurysms of the basilar and

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vertebrobasilar junction who underwent 13 bypasses and flow reduction (2). The bypass strategies included low-flow bypass from the superficial temporal artery (STA) as a donor to the PCA or SCA, or double-barrel STA-to-PCA and STA-to-SCA bypasses for flow augmentation. Russell et al. reviewed bypasses to the PCA or SCA using saphenous vein conduits, and the

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outcomes for the 217 total patients reported in the literature were as follows: 135 excellent (62%), 26 good (12%), 30 poor (14%), and 26 dead (12%) (3). Published series about complex posterior fossa aneurysms tell us that we still have not found a safe satisfactory treatment for

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such patients. Nonetheless, this does not invalidate the strategy. The formidable natural history of these lesions is very poor and justifies aggressive treatment.

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The advances in endovascular options offered by flow-diverters provide new therapeutic opportunities that are further diminishing the necessity for open surgery for many kinds of complex aneurysms. However, much to the disappointment of the cerebrovascular community, flow diverters have not proven particularly successful for managing fusiform vertebrobasilar aneurysms. Combining endovascular and open approaches, bypass for distal flow reconstruction or redirection, and parent artery occlusion can still be a valuable option. Open surgery as

ACCEPTED MANUSCRIPT Nakaji & Belykh 5 described in this issue is indicated in those patients for whom maximum medical therapy has failed. Arguably, using the occipital or superficial temporal arteries as donors would be simpler, allow single bypasses, and still might supply sufficient flow, in contrast to the short vascular

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grafts from the external carotid artery (ECA) or common carotid artery (CCA) that the authors chose. Also, indirect flow measurement using quantitative magnetic resonance angiography, or direct flow measurement of the recipient vertebral artery and donor anastomotic vessel or graft

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using a microprobe before and after bypass, could arguably help to quantify the amount of blood flow needed. This would avoid hypo- or hyperperfusion, and therefore provide a better selection

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of the type of donor needed.

In general, grafts are considered only when superficial arteries are hypoplastic or unavailable for flow augmentation bypass. High rates of bypass patency using the vertebral artery as a recipient without complications, despite an increase in the number of anastomosis

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(ECA/CCA-graft-VA) as reported in this article, deserve appreciation. The vertebral artery is an attractive donor because many patients have two, so those with balanced circulation can easily donate flow, and temporary occlusion is relatively safe. However,

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the vertebral artery is not frequently used as a donor. Dissection of V2 and V3 segments requires a relatively uncommon approach, which is usually substituted by more familiar approaches for

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dissection of the superficial temporal artery, occipital artery, or carotid bifurcation as donors. Anterolateral exposure of the V2 segment between the C1 and C2 transverse processes may be advantageous, even if it requires C2 nerve root sacrifice as described in the article. This exposes about 2 cm of the vertebral artery without significant bone removal, as is otherwise needed in the mid-cervical levels of vertebral artery. Fundamental to this kind of work is the high level of skill needed to successfully accomplish the whole bypass procedure with a high long-term patency

ACCEPTED MANUSCRIPT Nakaji & Belykh 6 rate without significant morbidity. We strongly believe that to improve outcomes, various possible strategies and techniques should be published and discussed. Overall, endovascular techniques are powerful and offer great advantage in many cases;

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yet the choice of management strategy should not be hampered because a lack of expertise makes one of these more exotic options unfeasible. In the future, bypass cases may become rarer, but, in reality, this only means that the skills to do bypasses must be perfected for when they are

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needed. We do not want to come to a point when we cannot do bypasses because we are bad at them. Simulation and practice in the laboratory are highly relevant and indeed are more

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applicable to rehearsal for vascular bypass than for many other kinds of surgery. A high level of subspecialization is desirable for treating patients with these rare conditions; yet also, the skills needed should be studied and practiced by all cerebrovascular neurosurgeons, if not all neurosurgeons in general. The field of bypass is one that requires a

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creative, artistic approach; a broad and deep knowledge of regional cerebrovascular anatomy, including that outside the brain; and a high degree of skill. We applaud the innovators who do not shy from complex cerebrovascular challenges, but who are rather willing to bring their

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imagination and expertise to bear for their patients who otherwise might have few viable options.

ACCEPTED MANUSCRIPT Nakaji & Belykh 7 References 1. Kalani MY, Ramey W, Albuquerque FC, McDougall CG, Nakaji P, Zabramski JM, Spetzler RF. Revascularization and Aneurysm Surgery: Techniques, Indications and

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Outcomes in the Endovascular Era. Neurosurgery 2014.

2. Kalani MY, Zabramski JM, Nakaji P, Spetzler RF. Bypass and flow reduction for complex basilar and vertebrobasilar junction aneurysms. Neurosurgery 2013;72:763-775.

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3. Russell SM, Post N, Jafar JJ. Revascularizing the upper basilar circulation with saphenous

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vein grafts: operative technique and lessons learned. Surg Neurol 2006;66:285-297.

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