Elsevier

World Neurosurgery

Volume 107, November 2017, Pages 314-321
World Neurosurgery

Original Article
Internal Maxillary Artery to Upper Posterior Circulation Bypass Using a Superficial Temporal Artery Graft: Surgical Anatomy and Feasibility Assessment

https://doi.org/10.1016/j.wneu.2017.07.158Get rights and content

Background

Revascularization of the upper posterior circulation (UPC), including the superior cerebellar artery (SCA) and posterior cerebral artery (PCA), may be necessary as part of the surgical treatment of complex UPC aneurysms or vertebrobasilar insufficiency. The existing bypass options have relative advantages and disadvantages. However, the use of a superficial temporal artery graft (STAg) in a bypass from the internal maxillary artery (IMA) to the UPC has not been previously assessed. We studied the surgical anatomy and assessed the technical feasibility of the IMA-STAg-UPC bypass.

Methods

Fourteen cadaver heads were studied. The STAg was harvested proximally from about 15 mm below the zygomatic arch. The IMA was exposed through the lateral triangle of the middle fossa. The IMA-STAg-UPC bypass was completed using a subtemporal approach.

Results

The bypass was successfully performed in all specimens. The average length of the STAg from the donor to the recipient was 46.4 mm for the s2 SCA, and 49.5 mm for the P2 PCA. The average distal diameter of the STAg was 2.3 mm. More than 83% of STAgs had a diameter of ≥2 mm distally. At the point of anastomosis, the average diameter of the SCA was 1.9 mm, and the average diameter of the PCA was 3.0 mm.

Conclusions

The proposed bypass is anatomically feasible and provides a suitable caliber match between the bypass components. Our results provide the anatomic basis for clinical assessment of the bypass in tackling complex lesions of the vertebrobasilar system requiring revascularization.

Introduction

Complex and giant aneurysms of the vertebrobasilar system are challenging lesions.1, 2, 3, 4 If left untreated, most of these lesions can be deadly.3, 5 Neither standard microsurgical clipping techniques nor endovascular treatment methods have been successful in tackling these lesions.6, 7, 8, 9, 10, 11, 12 On the other hand, Hunterian ligation of the basilar artery is not a risk-free option to treat these lesions.1, 5 However, occlusion of the basilar artery proximal to the lesion combined with revascularization of the efferent branches may minimize neurologic complications and allow for a definitive treatment.2, 4, 13, 14, 15 When selected carefully, patients with vertebrobasilar insufficiency (VBI) syndrome may also experience favorable surgical outcomes after revascularization of the rostral brainstem.16, 17, 18, 19, 20, 21

Revascularization of the posterior cerebral circulation is technically difficult and associated with high morbidity and mortality when associated with complex aneurysms or VBI.4, 13, 17, 18, 22, 23, 24 The upper posterior circulation (UPC) vessels, including the superior cerebellar artery (SCA) and posterior cerebral artery (PCA), are accessible through the subtemporal approach, or pretemporal and orbitozygomatic modifications of the pterional approach.1, 18, 25, 26, 27, 28 However, because of narrow and deep surgical corridors, these approaches may not provide optimal access for completing a bypass to the UPC.26, 29

Generally, the bypass is targeted to the segment of the PCA and/or SCA lying anterior or lateral to the mesencephalon (i.e., the P2 or s2 segment).30 The superficial temporal artery (STA) has been commonly used for this purpose.17, 19, 20, 22, 27, 31 However, because the STA narrows progressively in its course, it may not provide sufficient flow to the recipient territories.31, 32, 33, 34 In such cases, an extracranial (EC)-intracranial (IC) bypass using an interposition graft may provide adequate flow. Interposition grafts such as the radial artery graft (RAG) or saphenous vein graft (SVG) between the external carotid artery (ECA) and SCA/PCA may be associated with caliber mismatch and complications from hyperperfusion syndrome or graft occlusion.16, 35, 36

Recently, IC-IC bypasses have gained recognition for the treatment of complex vascular lesions, including dolichoectatic vertebrobasilar aneurysms.4, 37, 38 There are several reasons that make IC-IC bypasses appealing and advantageous; for example, the short distance between the donor and recipient, protection of the entire bypass by the cranial vault, and optimal caliber match between the donor and recipient. However, IC-IC bypass to the UPC complex is limited by its anatomic complexity.37 The in situ SCA-PCA side-to-side bypass is an elegant solution,38, 39, 40, 41 but it is relatively difficult to perform, and sometimes, both arteries may need to be occluded to address a basilar apex disease. Furthermore, this technique does not work for VBI syndromes.

Recently, we have proposed the use of a proximally harvested STA graft (STAg) for intermediate-to-high-flow bypass from the internal maxillary artery (IMA) to the middle cerebral artery (MCA) territory.42, 43 We used a harvesting technique for the IMA through the lateral triangle of the middle fossa previously reported by our team, to decrease the graft length and maximize the caliber match between the graft and the MCA.42, 44 Inspired by the promising features of the IMA-STAg-MCA bypass, we conducted the present anatomic study to 1) assess the feasibility of IMA-UPC bypass using an STAg and 2) assess the caliber match and graft length to help predict long-term graft viability.

Section snippets

Methods

Fourteen cadaveric heads (28 sides) were prepared for surgical simulation using our protocol, including a customized embalming formula.45 This novel embalming formula enables realistic brain retraction, making cadaveric surgical simulation similar to real surgery. Each head was placed in a 3-pin freedom clamp (Mizuho America, Union City, California, USA) in the lateral position. The vertex was slightly tilted toward the floor. A temporal craniotomy was completed flush with the middle fossa

Measurements

The following parameters were measured: 1) diameter of SCA and PCA at the point of anastomosis; 2) diameter of distal STAg at the point of anastomosis; and 3) length of the STAg used to complete the bypass.

Results

The IMA-STAg-PCA and IMA-STAg-SCA bypasses were successfully completed in all specimens. More than 83% of STA grafts had a diameter of ≥2 mm distally. Average diameter discrepancy between the distal STAg and the recipient artery was 0.5 mm. The average required length of the STAg was <50.0 mm. The data of all the bypass features are presented in Table 1.

Discussion

This study shows that the IMA-STAg-UPC is technically feasible. We have successfully used the STAg to complete an interposition bypass between the IMA and lateral mesencephalic segments of the SCA and PCA. This technique may be added to the current armamentarium for revascularization of the UPC in cases of complex basilar apex lesions and vascular insufficiency syndromes of the posterior circulation.

Conclusions

This study shows that the IMA-STAg-UPC bypass is a feasible technique for revascularization of the UPC. It may be used in various diseases, including complex aneurysms and vascular insufficiency syndromes. Advantages include short length of the graft; total IC course of the bypass; exposure of the donor, graft, and recipient through a single craniotomy; and proper caliber match between the bypass components. This technique adds to the current armamentarium of the vascular neurosurgeon

Acknowledgments

We would like to express our gratitude to the body donors and their families, which, through their altruism, contributed to this project. We also thank Ken Probst for the illustration.

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    Conflict of interest statement: A.T.M.'s research fellowship at the Skull Base & Cerebrovascular Laboratory at the University of California San Francisco is supported by funding from Medtronic.

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