Speciality: =20 Neurology

Topic: Cerebral Revisualization

Experts: =20 Basant K Misra, Jayant Thorat, P P Ashok, Vrajesh Udani, = Department of=20 Neurosurgery, Neurology & Pediatrics, P D Hinduja National Hospital = &=20 Medical Research Centre,V S Marg, Mahim, Mumbai =

Introduction

Cerebral = revascularization, an=20 important component of neurovascular surgery, is required for (i) flow=20 replacement after = parent=20 vessel occlusion / sacrifice in the treatment of complex aneurysms, = skull base=20 tumours and (ii) flow = augmentation=20 in selected patients of cerebral ischaemia. While flow replacement = is=20 accepted as an established indication for cerebral revascularization, = flow=20 augmentation for cerebral ischaemia is still controversial. The landmark Extracranial =96 = Intracranial=20 (ECIC) bypass study addressed this question : does Superficial Temporal = Artery=20 Middle Cerebral Artery (STA-MCA) bypass actually reduce the risk of=20 stroke¹. The results of this modern, = randomized,=20 controlled trial were clear: ECIC bypass did not diminish risk of = stroke. Although, the study failed to = identify=20 any subgroup of patients who would benefit by STMC bypass over best = medical=20 therapy, there nonetheless is a finite number of patients with cerebral=20 ischaemia, patients who have persistent symptoms of cerebral ischaemia = with=20 documented hypoperfusion, without infarction or other intracranial = causative=20 mass lesions, who are refractory to optimal medical management⁼and=20 are candidates for bypass². The impact of ECIC bypass study = has been=20 dramatic. The number of patients referred and undergoing STMC for = improving=20 ischaemia, one of the commonest operation pre 1985, became few and far=20 between. Generations of=20 neurosurgeons never had an opportunity to practice this procedure. = However,=20 there has been a renewed interest in ECIC bypass as it is now recognized = that=20 there exist a limited but definite indication for this procedure. Identification of the patients = most=20 likely to benefit from ECIC bypass and the therapeutic options available = to the=20 neurosurgeon in the treatment of these patients will be discussed in = this=20 chapter - Revascularization procedures other than ECIC bypass will not = be=20 discussed.

History

Conley, a head and = neck surgeon,=20 first performed a saphenous vein graft (SVG) bypass for the cervical = internal=20 carotid artery (ICA) = during the=20 resection of a neck tumour in 1953³. The pioneering work of = Yasargil=20 in late 1960=92s including the first ECIC STMC bypass led to the = foundation of=20 revascularization in Neurosurgery^(4). The first case of SVG from = common=20 carotid artery (CCA) to intracranial ICA was reported by Lougheed and = his=20 colleagues⁵. = Over the=20 last 2 decades many authors have made significant contribution in the = field of=20 cerebral vascularization. = The=20 seminal works of Fisch, Glasscock, Miyazaki, Sekhar, Spetzler and Sundt = need=20 special mention^3,6-7.Ausmann was probably the first to use = radial=20 artery graft (RAG) for intracranial bypass, gaining from the experience = of=20 cardiac surgeons⁸ Tulleken et al. described the EXCIMER laser = assisted high flow bypass with minimal blood flow = interruption⁹. The first author has pioneered = cerebral,=20 both direct and indirect, revascularization in=20 India^10-12.

Indication of ECIC bypass

The two main = indications of ECIC=20 bypass are for :

A. = flow replacement

B. =20 flow augmentation

A. Flow Replacement : It is a = well=20 established indication to perform ECIC bypass following planned = occlusion of ICA=20 and occasionally vertebral artery which is sometimes necessitated in the = management of giant and complex aneurysm because of its inaccessible = location=20 eg. intracavernous carotid aneurysm. In patients with anticipated = cerebral=20 ischaemia after arterial occlusion, bypass grafting has been performed = with good=20 results (2-3,6-12-13). There exists controversy, however, in deciding = whether to=20 bypass every patient undergoing planned carotid occlusion, universal revascularization or = bypassing=20 only patients with inadequate collaterals, selective=20 revascularization¹³. =20 While the Spetzler group and Sekhar have advocated universal=20 revascularization, many other authors like Tew, Ojemann, Ogilvy, Crowell = and=20 Awad believe in selective revascularization^14-17. Lawton et = al.=20 advocate universal revascularization following carotid occlusion because = of the=20 following reasons¹³.

i. = ; =20 balloon occlusion test (BOT) is an invasive test with a = permanent neurological morbidity of 0.7%¹⁸

ii. = ; =20 BOT has a high false negative rate with an acute stroke = risk=20 2-22.7% and a delayed stroke risk of 0-1.9% per year^19-21 =

iii. = ; =20 in contrast, universal revascularization incurs an = acute stroke=20 risk of 7-10% and a small delayed stroke risk from symptomatic graft = failure=20 (0.2-0.3%) per year.

The Cincinnati group = favours=20 =93selective revascularization¹⁴. =20 They advocate BOT followed by permanent carotid occlusion if the = patient=20 has no clinical changes during 30 minutes of test occlusion. They reserve revascularization = in the=20 following patients:

1. who clinically = fail their BOT=20 or have CBF less than 30 cms/100g/ min based on Xenon enhanced CT = (patients who=20 pass their BOT but have asymmetry on SPECT if Xenon CT is not = performed),

2. = following SAH because of increased risk of aggravating=20 vasospasm,

3. = who have contralateral carotid aneurysms,

4. = with isolated middle cerebral artery circulation.

We have been = employing BOT to=20 select patients for cerebral revascularization. We employ BOT for 15 minutes = and if=20 there is no clinical symptoms we induce challenge hypotension by = reducing BP by=20 20% from the basal level with sodium nitroprusside. If the patient has no clinical changes and = there is no=20 delay in cerebral circulation we presume the patient is safe for permanent carotid=20 occlusion. More recently, = we tend=20 to favour revascularization even if they pass BOT especially in younger=20 patients.

The other indication = of ECIC=20 bypass has been flow replacement when an elective ICA sacrifice is = planned in an=20 attempt to achieve a total excision of a skull base tumour eg. = meningioma=20 involving cavernous sinus. = We do=20 not think this is a viable option today especially with the advent of = Gamma=20 Knife Radiosurgery (GKR) which can control residual tumour in the = cavernous=20 sinus following subtotal excision. Moreover, sacrificing the carotid in = the=20 cavernous sinus in a skull base meningioma more often than not fails to = cure the=20 tumour anyway. It may be = logical,=20 however, to resort to this strategy sometimes in a low grade malignant = tumour if=20 a radical excision can prolong life or lead to cure. Additionally, = patients who=20 fail initial surgical resection and adjuvant therapies (i.e. = radiosurgery) and=20 present with tumour growth may be candidates for parent vessel occlusion = and=20 total tumour resection in combination with ECIC bypass^{22 =}.

B. Flow Augmentation : While flow = augmentation to prevent stroke is not a routine indication following the = 1985=20 ECIC bypass study, there are special cases where bypass may be = worthwhile in=20 some patients, as one of the major limitation of ECIC bypass trial was = that=20 there was no method available at the time of trial to assess the status = of=20 cerebral haemodynamics in the distal cerebral circulation. These are patients who have = persistant=20 symptoms of cerebral ischaemia with documented hypoperfusion without = infarction=20 or other intracranial causative mass lesion, who are refractory to = optimal=20 medical management². =20 Current indication for bypass procedures in patients with = symptomatic=20 cerebral ischemia include the following^23-25

1. = patients unresponsive to optimal medical treatment with =

=B7 =20 responsible lesions inaccessible for direct = surgery eg.=20 carotid siphon stenosis

=B7 =20 a region of reduced perfusion has been = documented either=20 by direct measurement of regional CBF or by metabolic studies.

2. = moya moya disease

3. = traumatic ICA injury

Preoperative Preparation

General patient = factors taken=20 into consideration for gauging the risk are age, hypertension, diabetes=20 mellitus, smoking history, hypercholesterolemia, cardiovascular disease, = previous evidence of cerebrovascular disease and Marfan=92s syndrome. = Test for=20 protein C, protein S, Factor V Leyden in-patients with previous history = of=20 stroke should be carried out. Patients with ischemic heart disease must = undergo=20 stress thallium test or a persantin =96 thallium test evaluation of = cardiac=20 function. For patient with skull base tumours, previous history of = radiotherapy,=20 malnutrition, chemotherapy and hypercoaguable state are important.

Cerebral angiography = (DSA or=20 Digital Subtraction Angiography) displays vascular anatomy as well as = allows for=20 functional testing such as Amytal testing and balloon occlusion. It is important to study the = collateral=20 circulation with a BOT to detect patient=92s tolerance to temporary=20 occlusion. However, in = patients=20 with bilateral ICA aneurysms, this test is contraindicated. The DSA = study also=20 provides the information on the sizes of the various intracranial = vessels and=20 neck vessels, presence of atherosclerosis and Fibromuscular = Dysplasia. In case of chronic ischemia, = the pattern=20 of collateral supply can be accurately assessed with an aim to preserve = all=20 existing collaterals. = Thus it may=20 be necessary to preserve the superficial temporal artery (STA) or the = meningeal=20 artery if these are found to be providing the collaterals. The external carotid arterial = system is=20 studied carefully. The = importance=20 of the external carotid system may require establishment with amytal = injection=20 in selective cases. BOT = with=20 provocative hypotension (20% below patient=92s SBP value) may increase=20 sensitivity. Concomitant = EEG=20 monitoring may also help pick up non eloquent region ischemic = deficits. Cerebrovascular reserve can be = tested=20 using either stable Xenon CT scan or SPECT using Tc-HMPAO performed = before and=20 after administration of acetazolamide. =20 A relative decrease in the regional perfusion after acetazolamide = indicates =AF=20 cerebrovascular reserve capacity. =20 Other pre-operative investigations which can be used are PET = scanning, Xe=20 washout CBF measurement, Transcranial Doppler (TCD), duplex scanning of = the=20 extracranial carotid artery and oculoplethysmography.

Instrumentation

Depending on the = vessel diameter=20 the monofilament suture such as, 10-0, 9-0 or 8-0 or 7-0 prolene should = be used.=20 Fine needle holders should be used to handle the fragile vessel walls = and the=20 sutures. For working at a = depth,=20 bayoneted instruments are essential. =20

Types of Bypass : = Revascularization can=20 be classified as :

1. = Direct : vessels are anatomosed directly with immediate = revascularisation and

2. = Indirect : = where=20 no appropriate recipient or donor artery is available eg. Encephalo duro = arterio=20 synangioses (EDAS), Encephalomyo synangioses (EMS) and omental = transposition.=20

Direct bypass = procedures=20 are further divided into two categories depending on their flow volume : = low=20 flow and high flow bypasses. = The=20 low flow bypass includes the STA =96MCA. MMA =96MCA side-to-side and = arterial and=20 venous short interposition grafts. These techniques are normally used to = cover a=20 relatively small area where large volumes of blood are not necessary = because of=20 small caliber of the donor vessel and low inflow from terminal branch. =

The high flow bypass = includes the=20 ECA / ICA =96 MCA and ICA =96 ICA anastomoses, which are suitable for = supplying=20 large areas when long saphenous vein or RA grafts are used. The high = flow bypass=20 supplies enough blood flow to cover the entire MCA and ACA = territories. The flow through the saphenous = vein=20 graft is enough to prevent ischemia in patients with an isolated ICA and = no=20 collaterals and on average, the graft carries about 110 ml/min blood=20 supply. The radial artery = graft on=20 the other hand carries abut half as much blood as the saphenous vein = graft and=20 hence may not be sufficient as the saphenous vein graft and hence may = not be=20 sufficient to replace a carotid when there is no collaterals. Bypass = technique=20 can also be classified into two types, based on whether grafts are a) = pedicle=20 grafts b) free grafts. = The pedicled=20 arterial grafts, such as STA and occipital artery grafts are mainly used = for low=20 flow bypass and the free arterial and vein grafts are used as high flow=20 bypass. Prior to surgery = it is=20 important to ascertain that the patient has a reasonable chance of = benefit from=20 the procedure irrespective of the risks of surgery.

Graft Extraction Techniques

Saphenous Vein

The saphenous vein = may be=20 harvested from the thigh or the leg depending on the requirement of the = calibre=20 and length of the graft. = The lower=20 limb is positioned with the hip externally rotated and flexed at the = knee. For the thigh, the femoal = pulse is=20 palpated and the incision made medially. =20 The vein is located and then traced distally by sequential = dissection=20 down the thigh to the adductor tubercle. =20 The small tributaries of the vein are double ligated to prevent = pull of=20 the ligatures under high flow pressure. =20 The vein is marked with methylene blue ink to help prevent = tortion during=20 the subsequent stages of surgery. =20 The dissected vein is covered with papaverine soaked = patties. At the time of extraction, the = vein is=20 ligated proximally and distally with different coloured ligatures to = identify=20 proximal and distal ends. = The vein=20 is finally harvested just after the anastomosis site is prepared. Heparinised solution is used = to flush=20 out the blood from the vein and to check for leaks. The leaks are repaired with = 6-0 prolene=20 sutures horizontal to the axis of the vein to prevent constriction of = the=20 lumen. For the leg, the = vein is=20 exposed on the posterior border of the medial tibial tubercule, where it = can be=20 palpated and traced upward medially to the knee and into the thigh. After anastomosis and before = releasing=20 temporary clamps / clips the methylprednisolone dose should be = administered to=20 protect the venous endothelium form denudation under the force of the = arterial=20 blood flow.

Radial Artery =

The Allen test should = be=20 performed to ensure good collateral flow between the ulnar and radial = arteries=20 in the palmar arterial arch. = If=20 possible, the non-dominant hand should be used. When the recipient artery is = less than=20 2.5mm in diameter, the radial artery is preferred. The artery is exposed at the = wrist and=20 traced proximally in the forearm, between the muscle layers, up to the=20 bifurcation of the brachial artery. =20 The venae commitantes is preserved except for a length of 2cms at = the two=20 ends. The branches are = ligated and=20 cut. To prevent vasospam = in the=20 artery, diltiazem hydrochloride is administered at a loading dose of=20 0.15-0.25mg/kg followed by a continuous I.V. infusion at 0.5-1.0=20 microgram/kg/min. The = artery is=20 left in situ till the anastomosis sites are ready. Just before extraction, the = radial=20 artery is temporarily clipped at the most proximal site and using the = pencil=20 Doppler the flow in the palmar arch is confirmed. The distal radial artery stump = in the=20 hand, after harvesting the radial artery, will be seen pulsating as = a further confirmation to the = integrity of=20 the collateral flow in the arch. = After harvesting the vessel, the artery is cannulated with a = short metal=20 venous cannula attached to a heparinized saline filled syringe. Some advocate using blood and = papaverine=20 solution (60mg of papaverine per 60ml blood). The artery is then pressure = distended=20 for short segments between the cannula and the fingers distally till it=20 =93pops=94. The fingers = are then=20 marched forward along the artery till the whole length is thus = distended. This will prevent spasm of the = vessel=20 after anastomoses. The = volar aspect=20 of the vessel is marked with methylene blue dye to ensure against = twisting=20 during storage or during anastomosis. =20 The artery is wrapped in papaverine soaked gauze until it is = ready for=20 anastomosis.

The wound is closed = after=20 confirming hemostasis to prevent compartment syndrome postoperatively. = The=20 closure is performed in 2-3 layers. =20 The deep fascia is closed in interrupted manner with 3-0 = polyglycolic=20 acid sutures followed by a subcuticular running 3-0 or 4-0 polyglycolic = acid=20 suture. No drains or = pressure=20 dressings are used. Avoid = circumferential adhesive after applying a sterile dressing pad. The forearm need not be = elevated. Postoperatively the capillary = filling in=20 the nail bed should be confirmed periodically as also the finger = movements.

Other Arteries=20

If smaller arteries = are needed=20 for interposition grafting then the following are used : occipital = artery,=20 superficial temporary artery or the superior thyroid artery.

Intraoperative Neuroprotection =20

The aim of = anaesthesia is to=20 protect vulnerable tissue from further ischemic insults as well as = protect the=20 brain during cross clamping from ischemia, while preventing = thromboembolism with=20 judicious use of anticoagulants and steroids. Proper positioning of the = patient with=20 head fixed in the Mayfield clamp is done to minimize the need to retract = the=20 brain and to provide maximum access to both ends of the anastomoses. = While=20 applying pins it is necessary to prevent hypertension especially for = aneurysm=20 patients. Lumbar drainage = of CSF,=20 intravenous mannitol, hyperventilation to maintain PCO2 (28-32mmHg), = analgesia=20 and anticonvulsants such as phenytoin sodium will allow maximal = relaxation of=20 the brain.

Cerebral protection = includes an=20 appropriate choice of anaesthetic drugs, maintenance of intravascular = volume,=20 avoidance of hyperglycemia and =20 proper monitoring of the relevant biochemical and physiological=20 parameters. During = vascular=20 occlusion, induced hypertension (20% above the baseline) and metabolic = brain=20 protection (with barbiturates, etomidate, or propofol) is instituted to = achieve=20 burst suppression. = Thiopentone=20 sodium in the dose of 15mg/kg loading and then 3-5mg/kg/hr can be used = while=20 avoiding hypotension. = Mild=20 hypothermia upto 34=B0C=20 is recommended. Hypothermia below 31=B0C=20 can cause cardiac irritability and should be avoided. A large dose of=20 methylprednisolone (20mg/kg body weight) is administered intravenously = before=20 grafting, because of experimental evidence that the venous endothelium = can be=20 protected by steroids when it is exposed to the arterial = circulation. 100 units / kg of heparin is = also=20 administered intravenously during the grafting procedure, to minimize /=20 thromboembolic complications. =

For creating an = anatomosis at a=20 depth, such as the supraclinoid ICA, it is important to minimize = retraction on=20 the brain. Therefore, it = is=20 important to fashion the craniotomy as low as possible with extradural = drilling=20 of the anterior clinoid process and early release of CSF from the basal=20 cisterns. Sylvian fissure = is opened=20 widely to a avoid retraction. =

Bypass procedures

Saphenous Vein Grafting

SVGs are technically = the most=20 challenging because of the turbulence created by the high flow in the = graft and=20 a variety of minor but important technical details.

Internal Carotid / External = Carotid Artery=20 to Middle Cerebral Artery Bypass (ICA / ECA =96 MCA) =

For cranial exposure, = a=20 frontotemporal craniotomy is performed; for many cranial base tumours = and=20 complex aneurysms, an orbitozygomatic osteotomy is also performed. Very = careful=20 epidural hemostasis must be maintained with bipolar cautery dural = tack-up=20 sutures, and Gelfoam or Surgicel, because considerable oozing can occur = after=20 heparinization

The slyvian fissure = is split=20 widely to expose the MCA stem and its divisions. The vein is then placed close = to the=20 anastomotic site to achieve tension free and kink free anastomosis. The end is prepared dissecting = its=20 terminal 3mm of loose adventitial tissue. =20 To create a fishmouth, the proximal end of the vein graft is = obliquely=20 divided, avoiding sites with valves and selecting an area with a thin = venous=20 wall. The vein being = larger in=20 diameter the fishmouth should be small. =20 The main trunk of the MCA and its major branches are = isolated. The distal anastomosis is = performed=20 using 8-0 monofilament nylon sutures. The superior or inferior division = is=20 selected and an appropriate segment is prepared for anastomosis. The ideal location for = connection of the=20 vein graft is at the site of bifurcation, because the bifurcation = orients the=20 blood flow along the axis of the MCA, reducing turbulence. = Contraindications to=20 the use of this large M2 bifurcation site are a small size of the MCA = (M2=20 segment), very proximal branching, and the origin of large = lenticulostriate=20 perforators from the M2 branches. The arteries are coated with 3% = papaverine to=20 relax any vasospasm. Under brain protection temporary clips are applied = on the=20 recipient artery segment to trap a length of at least 1cm. A triangular rubber dam is = slipped=20 underneath the isolated segment. The arteriotomy is performed with a No. = 11=20 blade or a knick is first made with the knifepoint and extended = longitudinally=20 with micro Potts scissors. = The size=20 of the arteriotomy should match the fishmouth end of the vein. Care is taken to include the = intimal=20 layer in each suture bite to prevent dissection and occlusion of the = vessel on=20 reperfusion. To = facilitate tying a=20 knot it is better to keep the suture length short after passing through = both the=20 walls of the proximated vessels. = The first suture is through the heel approximated on the distal = end of=20 the arteriotomy. This = will direct=20 the flow through the anastomosis proximally into the MCA. The vein graft is anchored at = both ends=20 of the arteriotomy with 8-0 nylon sutures. First the backside is sutured = by=20 interrupted sutures and then the vein graft is flipped over, and the = other side=20 is sutured. Before the = sutures are=20 tied, the vein graft and the arterial segment are flushed with = heparinized=20 saline solution and a temporary clip is place on the vein, approximately = 2cm=20 proximal to the anastomotic line. =20 The temporary clips on the MCA are then released and the suture = line is=20 inspected for leaks. = Large leaks=20 require a stitch, whereas small leaks can be stopped with the use of a = small=20 piece of fibrillar surgicell. = The=20 distal anastomosis must be completed within 60 minutes (preferably = within 30=20 minutes) after vascular occusion. =20

The cervical internal = carotid=20 artery (ICA) and external carotid artery (ECA) are exposed via an = incision along=20 the anterior border of the sterno cleido mastoid and dissection in the = carotid=20 triangle. If the ECA is = planned as=20 the donor artery, then it is exposed at least as high as the hypoglossal = nerve=20 and preferably approximately 3 cm above the common carotid artery = bifurcation.=20

A subcutaneous tunnel = is created=20 preauricularly from the cranial incision to the cervical incision. The = base of=20 the zygoma is drilled to fashion a conduit for the graft when it is = placed in=20 the preauricular position. = A chest=20 tube is used to tunnel the graft through it by gently pulling it through = with=20 tying sutures. The tunnel = must be=20 as wide as possible and hemostasis must be carefully maintained to avoid = the=20 formation of a hematoma. Once inside the tunnel care should be taken to = avoid=20 twisting it. This may be = confirmed=20 by temporarily distending the vein with saline if necessary.

The ECA is used as = a donor=20 vessel if there is no collateral circulation. The ICA is used as a donor = vessel if=20 there is at least some collateral flow and the ICA can be safely = occluded=20 temporarily. The CCA can = be used=20 for the proximal anastomosis with the help of a side biting Satinsky = vasular=20 clamp that will preserve flow through the rest of the CCA vessel while = allowing=20 the anastomosis to be completed unhindered. This way the brain does not = have to=20 suffer another vascular occlusive insult. =20

If the ICA is = selected then=20 before the anastomosis, the cervical carotid artery is occluded = proximally and=20 distally. The vein graft is pulled down, to place it under slight = tension. An oblique venotomy is made = and is=20 fish-mouthed to enlarge the opening to approximately 8mm. An oblique, teardrop-shaped = arteriotomy=20 is made on the carotid artery. = The=20 vein graft is anastomosed to the carotid artery in an end to side = manner, using=20 continuous 7-0 or 6-0 prolene sutures. The proximal anastomosis = can=20 usually be completed within 30 minutes, often within 20 minutes. The graft is de-aired by = puncturing the=20 vein near the distal vein clip after releasing the proximal CCA clamp. =

After completion of = the=20 anastomosis the proximal clip on the artery and the temporary clip on = the vein=20 graft are released. Flow = through=20 the graft is assessed with a micro-doppler probe, preferably one that = can=20 quantitatively measure flow. = If the=20 flow is acceptable, then the cervical ICA distal to the vein graft = attachment=20 site is is ligated. The ICA may also be occluded distal to the lesion to = maintain the patency of the vein graft and also improve flow to the = collaterals=20 from the ECA. The ICA may = also be=20 occluded endovascularly afterwards in the postoperative period. Intraoperative pencil doppler = is used to=20 confirm flow and patency of graft and recipient vessels. The neuroendoscope confirms the = anastomotic=20 site leaks and also allows for safe clipping of the intracranial vessels = avoiding the perforators. =

Intraoperative = angiography is=20 then performed to confirm the patency of the vein graft. Both anastomosis and the = entire graft=20 must be imaged. The speed = of flow=20 through the graft must be faster than that through the ECA. If the flow = through=20 the graft is poor, then a small venotomy is made approximately 2 cm = proximal to=20 the distal anastomosis and the flow through the graft is assessed from = both=20 ends. If the flow from = the distal=20 end is poor, then the anastomosis must be revised. If the flow from both ends is = good but=20 the graft flows poorly, then the problem is a kink created at the distal = anastomosis by the high-flow vein graft. =20 The solution to this problem is to pull the vein graft away from = the=20 anastomosis and anchor it to the dural edge. There may be kinking at the = proximal=20 anastomosis caused by excessive flow through the ICA. This can be corrected by = pulling the=20 anastomotic site inferiorly with a suture and anchoring it to the = adventitia of=20 the artery, approximately 1 cm inferior to the anastomosis.

Cervical =96 To =96 Supraclinoid = ICA Grafts=20

When the MCA is not = suitable for=20 intracranial anastomosis, the supraclinoid ICA can be used as the = recipient=20 vessel. The pterional = craniotomy=20 needs to be as low as possible with addition of orbitozygomatic = approach. The extradural drilling of the = anterior=20 clinoid process facilitates exposure of greater length of the distal = ICA. The site of anastomosis is = between the=20 ophthalmic and the posterior communicating arteries. The arachnoid over the ICA and = the=20 posterior-communicating artery (PCOM A) =20 is divided widely. = The ICA=20 is occluded just superior to the ophthalmic artery with a permanent clip = and=20 with a temporary clip just proximal to the PCOM artery. The artery is then sectioned = between the=20 clips and rotated laterally for suturing. The anastomosis is completed = in the=20 same fashion as for MCA anastomoses. Generally, a temporary clip is = placed on=20 the ICA just inferior to the anterior choroidal artery and another clip is placed on the = posterior=20 communicating artery. The = cut end=20 of the ICA is fish-mouthed. = The=20 vein graft is sectioned obliquely. =20 An end-to-end anastomosis is performed with 8-0 nylon or 7-0 = prolene=20 sutures. Sometimes the = intima of=20 the ICA is atherosclerotic at this level. =20 Care must be exercised to pass the needle through both the intima = and the=20 media, to avoid dissection. = After=20 the anastomosis has been completed, a temporary clip is placed on the = vein=20 graft. The vein graft is then led out through a wide dural opening in = the=20 clinoid space, brought around the anterior temporal dura, and passed = through a=20 preauricular tunnel to the cervical incision. The practice of first passing = a small=20 chest tube and then passing the graft through the chest tube facilities = graft=20 passage through the preauricular tunnel. =20 For vein grafts attached to the ICA, the preauricular tunnel is = preferred=20 to the postauricular tunnel, because of the shorter distance and the = more=20 physiological orientation of the graft through the clinoid space. The proximal anastomosis to = the ECA or=20 ICA is then performed as described earlier. After the temporary clips are = removed,=20 the SVG expands and may cause kinking of the distal anastomotic = site. A pexy may need to be = performed, by=20 pulling the graft back with a suture to the dura.

Cervical Carotid To Petrous ICA = Bypass=20

This procedure is = performed in=20 cases of upper cervical or petrous ICA aneurysms, dissection, tumours or = vascular trauma. For spontaneous dissections, anticoagualnt and = antiplatelet=20 therapy is first instituted. In the presence of persisting symptoms a = bypass=20 procedure may be required Cervical to petrous ICA precludes the need to = open the=20 dura unlike that in the cervical to supraclinoid ICA procedure. The = horizontal=20 segment of the petrous ICA is exposed after a temporal craniotomy and a=20 zygomatic osteotomy. The distal clip is placed just inferior to the = trigeminal=20 root. Proximal occlusion may be obtained in the neck or in the petrous = ICA bony=20 canal by passing a Fogarty catheter extraperiosteally and inflating it. = A=20 periosteal sheath surrounds the petrous ICA, and it must be opened near = the=20 anastomotic site. If possible, the surgeon should avoid sectioning the=20 sympathetic nerves. The = anastomosis=20 is performed either end to end or end to side. The vein graft is then led to = the=20 cervical incision through either a retroauricular or preauricular = tunnel. The=20 proximal anastomosis is performed as previously described.

Subclavian Artery =96Sphenous = Vein-Middle=20 Cerebral Artery Bypass

If the common = carotid, external=20 carotid and the STA are not available or suitable for bypass, then a = long graft=20 may be used from the subclavian artery. =20 A transverse incision over the medial third of the clavicle is = made to=20 expose the subclavian artery. The phrenic nerve is protected while the = anterior=20 scalene muscles are divided. The thoracic duct on the left side must be=20 protected and safely ligated if encountered to prevent postoperative=20 fistulas. With temporary = subclavian=20 occlusion, an end to side anastomosis with saphenous vein is performed = after=20 first tunneling the vein through a vascular trocar to the anastomtoic = site.=20 Usually 6-0 nylon interrupted sutures suffice for the proximal = anastomosis.

STA-Saphenous Vein-Posterior = Cerebral=20 Artery Bypass Graft

This is indicated for = inoperable=20 or unclippable posterior circulation aneurysms of the vertebrobasilar = system.=20 The position is supine with the ipsilateral shoulder elevated over a = sand bag or=20 a roll and the head turned to the contralateral side. The CSF drain is = placed=20 after induction for relaxation of the brain. The required length of STA = is=20 exposed and using this incision a flap is reflected over the posterior = temporal=20 region for a craniotomy. The temporal lobe is retracted and cisterns are = opened=20 preserving the vein of Labbe. = 10-12=20 cms length of SVG is usually harvested The P2 segment of the PCA is = selected for=20 an end to side anastomosis of the SVG, which directs the flow medially = towards=20 the P1 or the origin of PCA. Then the SVG is routed to the STA in the=20 subcutaneous tunnel and sutured end to side. As the basilar aneurysm may = rupture=20 under the force of the new flow, it may be necessary to simultaneously = clip the=20 aneurysm proximally if it is not feasible to trap the aneurysm. Similarly the ECA can be = selected for=20 this procedure if the STA is not suitable.

Common Carotid=20 Artery to Posterior = Cerebral Artery=20 Bypass with Saphenous Vein

This procedure is = similar to that=20 performed for the CCA to MCA saphenous vein bypass grafting. However for = the=20 exposure of the posterior cerebral artery (PCA), a subtemporal approach is = employed,=20 carrying the craniotomy anteriorly to the midzygomatic region and the = base is=20 drilled low and flat to minimize retraction on the posterior temporal = lobe. CSF=20 drainage via a preop lumbar drain, mannitol, thiopentone and head = elevation may=20 help relax the brain tension. While avoiding traction on the vein of = Labbe, the=20 temporal lobe is elevated with retractor gently to expose the PCA. The = arachnoid=20 is cut with microscissors to release the CSF from the crural cisterns. = The P2=20 segment which is devoid of major branches is selected for anastomosis. = The P-2=20 segment lies distal to the thalamo perforating, medial posterior = choroidal,=20 hippocampal and peduncualr arterial origins. The vein cut in beveled = fashion is=20 brought into the opening for anastomosis. The P-2 arteriotomy is made of = appropriate size to match the venotomy. The fishmouth of venotomy is=20 approximated with its heel distally on the arteriotomy and the toe end = on the=20 medial end of the arteriotomy. The suture technique is similar to that = used for=20 the MCA bypass. The proximal anastomosis is done end to side on the = CCA.

Common Carotid Artery to = Vertebral Artery=20 Bypass with Saphenous Vein

The patient is placed = supine with=20 shoulder ipsilateral to the bypass elevated on a sand bag. The head is = turned to=20 the contralateral side on a head pin with slight flexion laterally = towards the=20 floor. This allows exposure of the CCA in the neck as well as the = vertebral=20 artery posteriorly at the C 1 arch. The incision is designed in inverted = hockey=20 shaped fashion, starting in the midline at the C-1 spinous level and = extending=20 up the nuchal line before turning laterally to the transverse process of = the C 1=20 arch. Caution must be exercised when retracting the muscles as this may = tug on=20 the muscular branch of the vertebral artery thus bringing the vertebral = artery=20 into danger. The muscular branch should therefore be identified in the = sub=20 occipital triangle and cauterized or ligated and cut. The suboccipital nerve must be = similarly=20 identified and preserved. The posterior fossa craniotomy is performed = along with=20 partial suboccipital condylectomy in conjuction with C1 arch excision. = This=20 exposes the whole length of the vertebral artery from the C2 foramen to = the=20 dural entry. The CSF may be released as required from the basal cisterns = and the=20 cisterna magna to facilitate exposure and access to the distal vertebral = artery=20 site of anastomosis. The distal site is selected as per pathology = present. The=20 dense venous plexus surrounding the vertebral artery bleeds profusely = but can be=20 easily controlled with surgicell.

The proximal = anastomosis in the=20 neck is designed in such a fashion so as to prevent kinking of the graft = or=20 subjecting it to undue tension after anastomosis. This anastomosis is = end to=20 side to the common carotid artery or ECA after creating an arteriotomy = described=20 earlier in the CCA to MCA saphenous vein graft technique. A temporary = clip is=20 placed just near the distal anastomisis to facilitate de-airing the = graft after=20 release of the carotid clamps or snugs. We prefer to use the side biting = Satinsky vascular clamps to preserve flow while partially clamping the = CCA for=20 anastomosis.

In the posterior = circulation,=20 vertebral artery (extracranial) to vertebral artery (intracranial), = vertebral=20 artery to posterior cerebral artery (PCA) and ICA to basilar artery vein = graft=20 bypass procedures can also be performed. =20 The saphenous vein extracted from the leg is used for these=20 anastomoses.

Radial Artery=20 Grafting (RAG) :

Because the vessel = wall is=20 thinner, RAGs are easier to perform and because the arterial endothelium = can=20 support the slower flow through them and less turbulence is created by = the=20 slower flow, they are easier to keep open, compared with SVGs. The major problem with RAGs is = the=20 occurrence of spasm, which has been solved to a large extent with the = use of the=20 =93pressure distention technique=94. =20 However, because the flow through RAGs (40-70ml/min) is less than = that=20 through SVGs (70-140ml/min) a single RAG may not be sufficient to = prevent a=20 stroke for patients with an isolated ICA and no collateral vessels. In such situations, a SVG or = two RAGs=20 (one from the ECA and the other from the ICA, into each major branch of = the MCA)=20 should be used.

Anterior Circulation=20

When the RAG is = attached=20 proximally to the ICA or ECA, it is always anastomosed end-to-side = because of=20 the disparity of size between the vessels. =20 Distally, the RAG can be attached to the MCA-M2 bifurcation or = one of the=20 M2 branches. The RAG can = even be=20 attached to M3 branches, because of the size match between the = arteries. Because of the pliability of = the RAG, it=20 can be passed through pre or postauricular tunnel.

Posterior Circulation=20

RAGs are ideal for = bypass into=20 the PCA beyond a middle or upper basilar artery aneurysm or beyond a = tightly=20 stenotic basilar artery. = To perform=20 such a bypass, the surgeon must be certain of the connection between the = PCA and=20 the basilar artery. If = the P1=20 segment is atretic, thrombosed, or severely diseased, then this bypass = cannot be=20 used. A superficial = temporary=20 artery =96 to =96 superior cerebellar artery bypass is the only possible = option when=20 both PCAs are unsuitable. = After the=20 PCA anastomosis, the RAG can be connected proximally to the extracranial = vertebral artery, the ECA, or the MCA. =20

To perform this = anastomosis, an=20 anterior petrosal or subtemporal approach is used. The transpetrosal approach is = preferred,=20 because it increases the working space and cerebrospinal fluid can be = easily=20 drained from the cisterns. = The=20 temporal lobe is gently elevated after cerebrospinal fluid drainage and = the=20 tentorium is divided. The = P2=20 segment of the PCA is isolated 1 cm lateral to the mid-brain, a segment = devoid=20 of perforators is chosen for the anastomosis, and a rubber dam is placed = medial to it. After heparinization, blood = pressure=20 elevation and metabolic brain suppression, temporary clips are placed on = the=20 PCA. An oval arteriotomy = is made in=20 the PCA. The RAG is = sectioned=20 obliquely and fish-mouthed, to yield an opening of approximately 5mm in = length,=20 and the toe ends are anastomosed with 8-0 nylon sutures. The RAG is then placed flush = with the=20 brain, under a retractor if necessary. =20 The inferior side anastomosis is performed first, with 8-0 nylon=20 continuous sutures. The = RAG is then=20 flipped over to be closer to the tentorium and the adequacy of the = anastomosis=20 is confirmed by inspection inside the lumen. The superior side = anastomosis is=20 then completed with two 8-0 nylon running sutures or with interrupted=20 sutures. The RAG should = be oriented=20 against the direction of flow, to achieve maximal irrigation of the = basilar=20 artery. A temporary clip = is placed=20 on the RAG approximately 3cm lateral to the anastomosis and the clips on = the PCA=20 are removed. The RAG is = led through=20 a retroauricular subcutaneous tunnel to the ECA, through a subdural and=20 extradural tunnel to the extradural vertebral artery at the C1 level, or = through=20 a subdural tunnel to the MCA trifurcation. =20 The proximal anastomosis is then performed similarly to the = distal=20 anastomosis. After removal of the temporary clips, flow through the = graft is=20 assessed with a micro =96 Doppler probe. If a basilar artery aneurysm is = to be=20 trapped, then intraoperative angiography should also be performed, to = assess the=20 patency of the graft.

STA-MCA Bypass =

This was the most = common bypass=20 used in augmenting flow in cerebral ischaemia before the ECIC bypass = study. The superficial temporary = artery and its=20 two branches are traced with a pencil doppler and marked on the = skin. The whole procedure including = the skin=20 incision is done under microscope. =20 A =91Y=92 shaped incision is made on the skin directly overlying = the branches=20 of STA as distally as the branches can be traced and not on the stem=20 proximally. The incision = is then=20 deepened till the vessel is seen. =20 The branches are then traced proximally keeping the dissection = directly=20 over it so that the branches which take off on lateral sides of the = vessel wall=20 are left intact. The two = branches=20 are traced proximally upto the main stem of STA. The STA and its = branches are=20 then dissected off the fascia along with its vasa vasorum. The fascia is cut with = scissors at a=20 distance from the vessel wall, coagulating the small branches and tying = off the=20 large ones if any, far from the vasa vasorum. Thus the STA and its branches = are=20 mobilised completely from the fascia and covered with saline = patties. The edges of the scalp along = the STA=20 stem are also retracted with skin sutures to expose the underlying = muscle. The fascia with muscle = is then cut=20 in fan shaped fashion with a 3 cm =20 base under the stem of the STA. =20 The muscle is further split down the middle all along protecting = the=20 STA. The muscle bellies = are then=20 rotated out from under the vessel to be held with stay sutures without = undue=20 traction. The bone is = thus exposed.=20 The muscle bellies are kept covered with saline patties. Three burr holes are made, = anteriorly=20 just anterior to the origin of the anterior branch of the STA, second = burr hole=20 just posterior to the origin of the posterior branch and the third burr = hole at=20 the highest point of exposed bone. The branches of STA are held gently = out of=20 the way while the craniotomy is completed. =20 The dura is then opened in a trifoliate manner and the middle = leaf is=20 excised. The dural edges = are=20 reflected with sutures. = The=20 posterior end of the Slyvian fissure is identified and the emerging = branches of=20 the MCA are examined. One = of the=20 important factors to consider in the selection of a cortical artery for=20 anastomoses is its diameter and then length of artery available on the = cortical=20 surface. The largest = diameter M4=20 branches (around 1.4mm) is found in the angular = areas^23,24. Usually a branch of the = superior lip of=20 the slyvian fissure is selected. If the most suitable segment of artery = selected=20 has any large branches then these too must be clipped with temporary = clips=20 before anastomosis begins. The rubber dam of a colour which contrasts = with that=20 of the suture material used is placed under the segment of the recipient = artery. The rest of the = brain is=20 covered with gel foam. Whichever branch is dominant and is most suitable = to=20 reach the recipient artery is selected as the donor artery. A temporary aneurysm clip is = applied on=20 the main stem of STA and the branch is tied at the distal most point and = cut.=20 The STA free end is cut obliquely to fishmouth it. Attention is then = directed to=20 the recipient vessel to which temporary clips are applied under brain = protection=20 measures. The arteriotomy = is=20 created on the vessel, longitudinally, of size to match the fishmouth = end of the=20 STA. The heel is sutured = first=20 distally on the artery, followed by the toe end of the fishmouth, to the = other=20 end of the arterotomy. = This ensures=20 flow proximally to the more important perforators of the MCA and ICA, = which=20 supply critical structures. = One=20 side is sutured first by interrupted 10 =910=92 mono filament nylon = sutures followed=20 by the other side after flipping the STA over. The suture bite is taken = through both=20 the walls and cut to length of 3-4 cms. This short length allows = visualization=20 under microscope for ease of tying a knot without entangling long = lengths of=20 sutures. It is = important to=20 ensure taking the intimal layer in the bite as otherwise the anastomosis = may not=20 remain patent. It is = critical also=20 to avoid taking the opposite wall of the artery while suturing one = side. This can be avoided by taking = a single=20 midway suture on each side immediately after the first end sutures are = applied=20 on the arterotomy, before continuing with the anastomosis. Usually 4-5 sutures on each = side are=20 sufficient to complete the anastomosis. The anastmosis is then checked = for leaks=20 by releasing the distal clip on the recipient artery followed by the = proximal=20 MCA clip and lastly the STA clip. =20 The leaks if any are easily controlled with small fibrillar = surgicell or=20 pledgets or gelfoam over which micro patties are then placed for 5-6 = minutes,=20 the patties are then removed under saline irrigation. More fibrillar surgicell can = be added=20 for any latent ooze present. = The=20 anastomosis and the vessels are covered with patties soaked in = papaverine. The other division of the STA = is then=20 put on the brain surface while it continues to course out to the scalp = through=20 the burr holes. The = temporalis=20 muscle flaps are then split in the vascular plane of its intermuscular=20 septum. The split = thickness (inner)=20 flaps are rotated back to be sutured to the dural edges which are = trimmed=20 accordingly. While doing = so the STA=20 and its divisions are not to be compressed. The bone flap is the nibbled = off to=20 accommodate the STA and the inner bellies of the muscle. The outer bellies are to be = sutured over=20 the bone after it is fixed with miniplates and screws. It is advisable to confirm = patency of=20 the STA with Doppler at each stage of the closure to prevent compromise = of the=20 anastomosis. The scalp = flaps are=20 then sutured carefully avoiding compression of the STA and its branches. =

Occipital=20 Artery =96 Middle Cerebral Artery Bypass

The occipital artery = has tendency=20 to branch off into several small vessels, which are not suitable for=20 anastomosis. It is also = invested in=20 a dense adventitia with venae commitantes, which make its dissection=20 difficult. Therefore, the = artery=20 should be marked from its entry to the scalp at the mastoid groove for a = length=20 of 12 cms with pencil doppler. = The=20 incision over the posterior temporal region to expose the posterior = sylvian=20 fissure should be taken down to preserve the posterior division of the = STA,=20 which supplies the flap. = The=20 Occipital artery is tunneled to the M2-M3 artery for anastomosis done in = the=20 fashion described for the STA =96 MCA bypass. For a high flow bypass, a = short length=20 SVG graft from the occipital artery stem to M2-3 branch can also be = done. Both anastomoses of the SVG = should be=20 end to side.

Occipital=20 Artery To Posterior Inferior Cerebellar Artery (Pica) Bypass=20

The patient is positioned prone, side or = sitting=20 with the head flexed forward. = The=20 course of the occipital artery is marked on the skin with Pencil Doppler = for=20 localisation. The length = of the=20 artery to be dissected should be sufficient to allow it to be mobilised = to a=20 depth at the site of the planned PICA anastomosis. The origin of the = occipital=20 artery is tracked from its entry to the scalp at the mastoid = process. The medial end of the incision = can be=20 then turned caudally to the level of the C1 arch, thus allowing for = suboccipital=20 craniotomy with excision of the C1 arch as required. The caudal loop of the PICA at = the=20 inferior level of the vermis is usually easily accessible for the=20 anastomosis.

Encephalo-=20 Duro-Arterio-Synangiosis

This is done for = patients with=20 cerebral ischemia such as =91moyamoya=92 disease. It is a low risk procedure. = This does not however provide = immediate=20 revascularization to the brain but rather encourages sprouting of new = vessels=20 between the pedicle and the ischemic brain surface.

The site of the = ischemic zone=20 determines the site of surgery. = The=20 anterior or the posterior branch of STA is selected depending on whether = the=20 frontal or the posterior frontoparietal region needs revascularization. = The STA=20 is prepared with a cuff of adventitia. A sleeve of muscle with = temporalis fascia=20 is also taken and deflected without tension while craniotomy is = performed and=20 the dura is opened parallel to the STA. =20 The burr holes are placed at the proximal and the distal ends of = the STA=20 course. The arachnoid is = opened and=20 the graft is placed onlay onto the brain. Some surgeons advocate = stitching the=20 STA to piamater. The = dural edges=20 are sutured to the fascia securing the pedicle. The bone flap is fashioned to = allow the=20 entry and exit of the STA without compromise of the graft and = refixed. The scalp is then closed = carefully. Additionally one can place = several burr=20 holes over critical regions of the brain and turning the dural flap and = galea=20 inwards onto the brain surface can over time provide racemose type of=20 neovascularization.

Omental=20 Grafting

Goldsmith has = proposed the use of=20 omentum as it provides for a long pedicle which can be tunneled. Dr. = Jacob=20 Abraham from Vellore, India had also advocated omental grafts for=20 ischaemia. This however = requires a=20 laparotomy and a bulky omentum may be difficult to handle in the cranial = cavity.

Closure

In general, the steps = for closure=20 are similar for all vascular grafts. =20 For extracranial to intracranial graft, a cruciate dural incision = is made=20 for the entrance of the graft, to prevent its occlusion by the suture = line. The adventitia of the graft = can be=20 sutured to the dural edges and fibrin glue is used to achieve a = watertight=20 seal. The rest of the = closure is=20 performed as usual. Graft = flow must=20 be assessed along the tunnel after closure, using a Doppler probe. This site is marked and used = for=20 postoperative checks as well. =

Post Operative Follow Up Monitoring

Postoperative care is = similar to=20 that for craniotomy patients. All patients are treated with daily doses = of=20 aspirin (325mg administered orally). =20 Extracranial to intracranial grafts are assessed by magnetic = resonance=20 angiography or CT angiography 3 months postoperatively and once per year = thereafter.

Postoperative Complications and Management

Besides the usual = postoperative=20 care followed for all patients with craniotomies, attention should be = paid to=20 certain details such as maintaining normal or slightly high blood = pressure,=20 preventing a hypercoaguable state and monitoring graft patency. Patients with SVGs are treated = with=20 daily doses of ecosprin 150 mgs as well as clopidogrel 75 mg twice a = day. Pencil doppler is used to = assess the=20 patency of the graft after discharge MRA / CTA is used at 3 months = follow up for=20 evaluation of intracranial grafts. =20

Potential = postoperative=20 complications specific to bypass include epidural hematomas, which may = be caused=20 by the intraoperative heparinization. =20 If epidural oozing is excessive during surgery, then the heparin = therapy=20 must be reversed with intravenously administered 50% protamine. If an epidural hematoma = occurs, it is=20 treated in the usual manner. =

Intraoperative graft = occlusion=20 usually occurs for technical reasons or because of a hypercoaguable = state. This problem must be corrected = during=20 surgery.

The postoperative = blood pressure=20 should be maintained in the high normal range of 130-150mm of Hg = systolic. But if a high volume conduit in = chronic=20 ischemic patients is used then such high pressure may cause break = through=20 bleeding and may cause an intracerebal hematoma. Hence, in such cases = the blood=20 pressure should be maintained in the normal range.

Postoperative graft = occlusion may=20 occur but is very rare if intra operative graft flow is good. The reasons for graft = occlusion include=20 : problems with the proximal or distal anastomosis, poor endothelium of = the=20 donor or recipient arteries (eg post thrombosis or post irradiation = changes),=20 kinking at the proximal or distal anastomosis of SVGs , severe = constriction of=20 the subcutaneous tunnel, significant size disparities between the graft = and=20 recipient vessels (resulting in severe turbulence) and spasm of the = graft or the=20 recipient artery. If a SVG is occluded postoperatively, then replacement = with an=20 entirely new graft is required. Spasm of the graft (RAGs) or the = recipient=20 artery can be treated with careful intraluminal angioplasty performed by = an=20 experienced neurointerventionalist. =20 Accelearated and delayed occlusion or stenosis may occur with = SVG=92s.

Personal Experience

Over the years the = first author=20 has performed 49 cerebral revascularization procedures, of which direct = bypass=20 was performed in 23 (Table 1). There were 12 pedicled grafts (STMC) and = 11 free=20 grafts (Table 2). All the = free=20 grafts (long saphenous graft in 5 and radial artery graft in 6) were = performed=20 to bypass inoperable giant aneurysms (Table 3) Fig 1 & 2. The bypass = patency=20 rate was 82%. All STMC procedures were performed in patients of = =91moyamoya=92=20 disease. There were a = total of 16=20 patients of moyamoya where revascularization was carried out (Table 4). = In 8=20 patients, 12 STMC anastomosis were carried out (Fig.3). All these = patients also=20 had additional EMS and EDAS along with STMC. Only 2/8 had significant = postoperative=20 ischaemic events. In the other 8 patients only EDAS and EMS were carried = out. 3 of these patients = developed=20 significant ischaemic event in the follow up period (Table 5). Emergency cerebral = revascularisation was=20 carried out in 3 patients as salvage procedures for vessel occlusion = following=20 complications of endovascular treatment (Table 6).

Conclusion

Indications of = cerebral=20 revascularization is still evolving. While universal revascularization = for=20 cerebral ischaemia is not accepted, there nonetheless remains a select = group of=20 patients with low haemodynamic reserve who immensely benefit from bypass = eg=20 moyamoya disease. Another = accepted=20 indication of revascularization is to bypass an inoperable / giant = intracranial=20 aneurysm, when parent artery is sacrificed. Inspite of the development of = the=20 technique 4 decades back, only few neurosurgeons have developed enough=20 experience in this field = because=20 the numbers of bypass has dropped dramatically following the STMC = trial. The experience in India is = particularly=20 limited^10-2,26-27. =20 However, there is renewed enthusiasm and interest in cerebral=20 revascularization and all young neurosurgeons should get aquatinted with = this=20 procedure by hands on laboratory training. =20

Acknowledgement

We are thankful to = Dr. Sumit Rai,=20 Clinical Fellow, Dept. of Neurosurgery for collecting the references and = Ms.=20 Gloria D=92Souza, Academic Secretary for preparing the manuscript.

References

1. = The EC / IC Bypass Study Group : Failure of = extracranial =96=20 intracranial artery bypass to reduce the risk of ischaemic stroke : = results of=20 an international randomized trial. =20 N Engl. J Med 313:1191-1200, 1985

2. = Spetzler RF, Hadley MN,. =20 Extracranial to Intracranial Bypass Grafting in Neurosurgery, = Wilkin=92s=20 RH, Rengachary SS (eds) : = 2^nd Eds McGraw Hill 1996 pp 2157-2167.

3. = Sekhar LN, Bucur S, Bank, MD, Wright WO Venous and = arterial=20 bypass grafts for difficult tumours, aneurysms and occlusive vascular=20 lesions. Evolution of = surgical=20 treatment and improved graft results. =20 Neurosurgery = 44 :=20 1207-24, 1999.

4. = Yasargil MG, Krayenbuhl HA, Jacobson JH, 2^nd = Microneurosurgical arterial reconstruction. Surgery 67 : 221-233, 1970. =

5. = Laugheeed WM, Marshall BM, Hunter M, et al. Common = carotid to=20 intracranial internal carotid bypass venous graft. Technical note J Neurosurg 34 = : 114-118.=20 1971.

6. = Spetzler RF, Fukushima T, Martin N. et al. Petrous carotid to = intradural=20 carotid saphenous vein graft for intracavernous giant aneurysm, tumour = and=20 occlusive cerebrovascular disease. =20 J Neurosurg 73 : 496-501, 1990.

7. = Sundt TM, Piepgras DG, Houser OW et al. Interposition saphenous vein = grafts for=20 advanced occlusive disease and large aneurysm in the posterior = circulation. J=20 Neurosurg 52: 205-215, = 1982.

8. = Ausman JI, Nicologg DM, Chou SN : Posterior fossa=20 revascularization : Anastomosis of vertebral artery to PICA with = interposed=20 radial artery graft. Surg Neurol 9:281-286, 1978.

9. = Tulleken CA, Verdaasdonk RM, Berendsen W, Mali WP : Use = of the=20 excimer laser in high-flow bypass surgery of the brain. J Neurosurg 78 : = 477-480, 1993.

10. Misra BK, = Nair S,=20 Rout D, Rao VRK. Emergency cerebral revascularization. In Abstracts,=20 38^th Annual NSI, PGIMER, Chandigarh, p 42, 1988.

11. Misra BK, = Rout D.=20 Moyamoya Disease. The = Indian=20 experience. In = Proceedings :=20 International symposium on Vascular lesions of the brain. Pp 85, = SCTIMST,=20 Trivandrum, 1989.

12. Rout D, = Misra BK,=20 Nazer Y, Rout A. = Extracorporeal=20 circulation in giant basilar aneurysm surgery. In Abstracts, 39^th = Annual=20 NSI, Indore, p53, 1990.

13. Lawton MT, = Hamilton=20 MG, Morcos JJ, Spetzler RF. =20 Revascularization and aneurysm surgery : current techniques, = indications=20 and outcome. Neurosurgery = 38:83-94,=20 1996.

14. Link MJ, = Tomsick TA,=20 Tew JM : Honoured Guest presentation : Therapeutic carotid occlusion. = Clin=20 Neurosurg 46 : 326-338, 1998.

15. Vishteh = AG, Alleyne=20 CH, Spetzler RF : Therapeutic carotid occlusion : the case for = prophylactic=20 bypass Clin. Neurosurg 46:339-350, 1998.

16. Carter BS, = Ogilvy=20 CS, Putman C, Ojemann RG. = Selective=20 use of ECIC bypass as an adjunct to therapeutic ICA occlusion. Clin = Neurosurg=20 46:351-362,1998.

17. Lee S, = Awad IA.=20 Therapeutic carotid occlusion : Current Management paradigm. Clin. = Neurosurg=20 46:363-391, 1998.

18. Tarr RW, = Jungress=20 CA, Horton JA et al. Complications of preoperative balloon test = occlusion of the=20 ICA : Experience in 300 cases. Skull base surgery 1 : 240-244, 1991. =

19. Drake CG, Peerless SJ, Ferguson = GG :=20 Hunterian proximal arterial occlsion for giant aneurysms of the carotid=20 circulation. J Neurosurg 81 : 656-665, 1994.

20. Origitano = TC,=20 Al-Mefty O, Leonetti JP, et al: Vascular considerations and = complications in=20 cranial base surgery. = Neurosurgery=20 35 : 351-363, 1994

21. Kak VK, = Taylor AR,=20 Gordon DS. Proximal carotid ligation for internal carotid aneurysms : A = long=20 term follow-up study. J = Neurosurg=20 39: 503-523, 1973.

22. Abdulrauf SI,=20 Extracranial-to-Intracranial bypass using Radial Artery grafting for = complex=20 skull base tumours. Technical note. =20 Skull Base 15:207-215, 2005

23. Kawashima = M, Rhoton=20 AL, Tanriover N, et al. =20 Microsurgical anatomy of cerebral revascularization. Part I : Anterior circulation. = J=20 Neurosurg 102:116-131, 2005.

24. Kawashima = M, Rhoton=20 AL, Tanriover N, et al. =20 Microsurgical anastomy of cerebral revascularization. Part II : = Posterior=20 circulation. J Neurosurg 102=94132-147. 2005.

25. Crowell = RM, Oglivy=20 CS, Choi IS, Gress DR. = Direct Brain=20 Revascularization, in Operative Neurosurgical Techniques, Schmidek H, = Sweet WH=20 (eds). Philadelphia WB = Saunders=20 1995 pp 909-928.

26. Misra BK, = Cerebral=20 Revascularization : Our Experience presented at Neurovas 2005. Bangalore = Sept.=20 2-5, 2005.

27. Sharma BS, = Mehta VS.=20 Cerebral Revascularization : Ind. J. of Cerebrovascular surgery 1:36-44, = 2005.=20

Fig. 1 a

Fig. 1 b

Fig. 2 a

Fig. 2 b

Fig. 2 c

Fig. 2 d

Fig 3 a