Subtemporal Transzygomatic Approach for Proximal STA to Proximal PCA Bypass Using A Radial Artery Graft

Cagatay Han Ulku 1, Aynur Emine Cicekcibasi 2, Sahika Liva Cengiz 3, Mehmet Erkan Ustun 3, Mustafa Buyukmumcu 2

Departments of 1Otolaryngology Head and Neck Surgery, 2Anatomy, 3NeurosurgerySelcuk University, School of Medicine, Konya - Turkey

Subjects and MethodsFive adult cadaveric specimens were dissected bilaterally. Cadeveric dissection protocol that was approved by the Selcuk University Institutional Review Board. In the supine position the head was turned 70° away from the side of dissection, tilted toward the floor. A preauricular vertical skin incision was used. The trunk of STA was identified easily at anterior of the tragus. As the zygomatic bone is approached, an incision is made in the deep layer of the temporal fascia. The deep fascia and periosteum are dissected from the zygomatic arch, and the zygoma is exposed 2 to 3 cm away from its root. The massetermuscle is divided from its attachment to the zygomaticbone and the temporalis muscle is elevated from the temporal bone to perform a minicraniotomy (Figure 1). 30°oblique posterior zygomatic arch osteotomy is achieved just anterior-superior of the condilar fossa and vertical zygomatic arch osteotomy is performed 1 cm posterior to the zygomaticomaxillary suture. In that way, integrity of the condylar fossa and temporomandibular function were protected. The zygomatic bone is removed and preserved for subsequent reattachment. The minicraniotomy began just above the zyomatic root, extending 2 cm superiorly and 3 cm anteriorly (Figure 2). The dura of the middle cranial fossa is then separeted under the surgical microscope. After the temporal lobe was retracted, the interpeduncular and ambient cisterns were opened, and the P2 segment of the PCA was exposed intradurally. A radial artery graft harvested from the forearm was passed through craniotomy, inside the dura, until it reached the P2 segment to which it was anastomosed in an end-to side fashion. Proximal to the zygomatico-orbital artery branch, the STA was transsected. The proximal side of the RAG was anastomosed end-to-end with the proximal STA using continuous suture with 8.0 nylon or 7.0 prolenesutures (Figure 3). The mean caliber of the STA (proximal to the zygomatico-orbital artery), PCA (P2 segment), and proximal and distal sides of the RAG and the length of the graft were measured using an electronic micrometer.

IntroductionPatients complaining with vertigo or dizziness, frequently seek treatment in neurology, neurosurgery or otolaryngology clinics. Vertebro-basilar insufficiency is one of the most common causes of central vertigo or dizziness. The most common posterior circulation bypass is between P2 segment of the posterior cerebral artery (PCA) and external carotid artery (ECA) or vertebral artery (VA)1-5. However, these techniques using graft materials have some limitations, namely they are long and tend to be associated with a low patency rate4-6. In this study, we aimed to investigate the use of a radial artery graft for bypass of the proximal STA to the proximal PCA (P2 segment) via oblique posterior transzygomatic-subtemporal approach. This surgery practiced on cadavers to make sure that this technique can be used safely on patients.

ResultsThe mean caliber of the STA at the side of anastomosis(proximal to the zygomatico-orbital artery) was 2.25±0.35 mm (range 2.0-2.55). The mean caliber of P2 segment of the PCA was 2.2±0.2 mm (range 2.0 to 2.4). The average length of the RAG was 56±3.2 mm (range 54 to 58 mm). The mean caliber of the proximal and distal side of the RAG was 2.5±0.25 mm (range 2.25 to 2.75 mm), 2.3±0.15 mm (range 2.15 to 2.45 mm) respectively.

The VA is used as the proximal vessel if it is the same size as and is well connected to the other VA. If the VA is markedly dominant and the other VA is small, the ECA is used as the proximal artery.We carried out an anatomical and a technical study to find out, whether the diameter of the proximal STA and the length of the graft are suitable to perform an anastomosis between proximal STA and proximal PCA and to see whether this surgery can be performed or not. In the present study, we performed subtemporaltranszygomatic approach. Arterial graft was used, as advised when the caliber of the recipient vessel is under 2.5 mm4. We have found that the calibers of proximal STA, radial artery and P2 segment of proximal PCA matches well, and as the mean caliber of these arteries are over 2 mm, such a bypass would provide sufficient blood flow. Before performing an anastomosis, preoperative angiography, would be useful to measure the caliber of the proximal STA and PCA. The advantages of the proximal STA to proximal PCA bypass using radial artery graft are as follows; 1. It would provide sufficient blood flow, as the mean caliber of the proximal STA is larger than 2 mm. 2. It may have a higher patency rate, as a short arterial graft was used. Short venous and radial artery grafts have been reported to have higher patency rates of 80-90%9,16. ECA or VA to proximal PCA bypasses using long venous grafts have lower patency rates (70-80%), although they provide high blood flow6,17. 3. The radial artery serves as a good interposition graft. Early occlusion of the graft itself seems to occur often with vein grafts2,17. The long-term patency of arterial grafts has been higher than with venous grafts18. 4. Such a bypass is not technically more difficult than ECA to proximal PCA bypass and does not require a second incision in the cervical region. 5. The graft makes a bending where it enters the cranium in ECA to the proximal PCA bypass. However, the graft between the proximal STA and PCA made no bending and followed nearly a straight course, which is vital in patency. Because when bending increases and kinking occurs, the blood flow diminishes and the graft may occlude6.

The disadvantages of the proximal STA to proximal PCA bypass using radial artery graft are as follows; 1. The anastomosis is in the sylvian fissure and not as simple as a single anastomosis on the surface, 2. The graft prolongs operation time and may lower the patency rate compared with a single anastomosis8. 3. To prevent cerebrospinal fluid leakage, the dura over the hole can be sealed with fibrin glue. 4. It requires a posterior oblique zygomatic osteotomy.

References1. Ausman JI, Diaz FG, Dujovny M. Posterior circulation revascularization. Clin Neurosurg 1986;33:331-43.2. Sundt TM, Piepgras DG, Houser OW, et al. Interposition saphenous vein grafts for advanced occlusive disease and large aneurysms in the posterior circulation. J Neurosurg 1982;56:205-15.3. Heros RC, Ameri AM. Rupture of a giant basilar aneurysm after saphenous vein interposition graft to the posterior cerebral artery : Case report. J Neurosurg 1984;61:387-90. 4. Sekhar LN, Wright DC, Olding M. Brain revascularization by saphenous vein and radial artery bypass graft. In: Cranial Microsurgery, Sekhar LN, Olivera ED eds. New York, Thieme; 1999. p. 581-600. 5. Sundt TM, Piepgras DG, Marsh WR, et al. Bypass vein grafts for giant anaurysms and severe intracranial occlusive disease in the anterior and posterior circulation. In: Sundt TM ed. Occlusive cerebrovascular disease, diagnosis and surgical management. Philadelphia, WB Saunders; 1987. p. 439-64.6. Diaz FG, Pearce JE, Ausman JI. Complications of cerebral revascularization with autogenous vein grafts. Neurosurg 1985;17:271-276.7. Ausman JI, Diaz FG, de los Reyes RA, et al. Posterior circulation revascularisation. Superficial temporal artery to superior cerebellar artery anastomosis. J Neurosurg 1982;56:766-76.8. Ausman JI, Nicoloff DM, Chou SN. Posterior fossa revascularization : Anastomosis of vertebral artery to PICA with interposed radial artery graft. Surg Neurol 1978;9:281-6.9. Little JR, Furlan AJ, Bryerton B. Short vein grafts of cerebral revascularization. J Neurosurg1983;59:384-8.10. Ausman JI, Diaz FG, de los Reyes RA, et al. Anastomosis of occipital artery to anterior inferior cerebellar artery for vertebrobasilar junction stenosis. Surg Neurol 1981;16:99-102.11. Ausman JI, Diaz FG, de los Reyes RA, et al. Superficial temporal to proximal superior cerebellararteryanastomosis for basilar artery stenosis. Neurosurg 1981;9:56-60.12. Hopkins LN, Martin NA, Hadley MN et al. Vertebrobasilar insufficiency. Part 2. Microsurgical treatment of intracranial vertebrobasilar disease. J Neurosurg 1987;66:662-74.13. Khodadad G. Occipital artery-posterior inferior cerebellar artery anastomosis. Surg Neurol1976;5:225-7. 14. Microsurgical anatomy of cerebral revascularization. Part II: posterior circulation.J Neurosurg. 2005;102:132-47.15. Hamada J, Todaka T, Yano S, Kai Y, Morioka M, Ushio Y. Vertebral artery-posterior inferior cerebellar artery bypass with a superficial temporal artery graft to treat aneurysms involving the PICA. J Neurosurg. 2002;96:867-71.16. Sekhar LN, Schramm Jr VI, Jones NF, et al. Operative exposure and management of the petrousand upper cervical internal carotid artery. Neurosurg 1986;19:967-982.17. Sen C, Sekhar LN. Direct vein graft reconstruction of the cavernous, petrous, and upper cervical internal carotid artery:lessons learned from 30 cases. Neurosurg 1992;30:732-743.18. Kamiyama H, Abe H, Yamauchi T, et al. Use of a radial artery graft in STA-MCA anastomosis and other recent improvements in reconstructive surgery. Jpn J Neurosurg 1992;1:4-13.

ConclusionThe proximal STA to proximal PCA bypass using a short radial artery graft can provide a sufficient blood flow, and may be a reasonable alternative over “ECA to PCA” bypass using long venous grafts. Subtemporaltranszygomatic approach was found to be suitable for such a bypass procedure.

Figure 1. STA; Superficial temporal artery,TB; Temporal bone,TM; Temporal muscle,ZA; Zygomatic arch,

Figure 2. STA; Superficial temporal artery,TB; Temporal bone,TM; Temporal muscle,ZA; Zygomatic arch, D; Dura,ZR; Zygomatic root.

Figure 3. STA; Superficial temporal artery,TB; Temporal bone,TM; Temporal muscle,ZA; Zygomatic arch,ZR; Zygomatic root, D; Dura,AS; Anastomosis side,RA; Radial artery graft.

DiscussionThe vertebro-basilar insufficiency is a common cause of central vertigo or dizziness. Several techniques are avaliable for posterior circulation bypass surgery, such as the occipital artery (OA) to posterior inferior cerebellarartery (PICA), OA to anterior inferior cerebellar artery (AICA) or superficial temporal artery (STA) to superior cerebellar artery (SCA) or PCA bypasses, a radial artery graft from the VA to the PICA or a long venous graft from the ECA or VA to PCA1-3,5,7-15. The caliber of the donor (OA and STA) and recipient (PICA, AICA or SCA) arteries are under 2 mm, so that blood flow may be insufficient. Procedures using the proximal PCA as the recipient and the ECA or VA as the donor vessel in the bypass are reported to be more protective1,2,4.