Revascularization Techniques for Complex Aneurysms and

Skull Base TumorsYoumans Chapter 380

Joshua R. DusickNestor R. Gonzalez

Neil A. Martin

Outline• Revascularization for the Treatment of Aneurysms• Revascularization for the Treatment of Skull Base Tumors• When Is the Collateral Circulation Inadequate and Bypass Necessary?• Preoperative Planning and Preparation for Bypass Procedures• Intraoperative Monitoring and Management• Type of revascularization procedures• Postoperative Management• Complication• Long-Term Graft Patency

Revascularization for the Treatment of Aneurysms

• Clipping or coiling of complex, giant, and fusiform aneurysms• Calcification or atherosclerotic thickening of the aneurysm neck or the

parent artery• Recurrent aneurysms after endovascular coil embolization

Revascularization for the Treatment of Skull Base Tumors

• Petrous and cavernous ICA• Benign• Meningioma, schwannoma, pituitary adenoma, angiofibroma, chordomas :

benign nature, should not resect artery• Stereotactic radiosurgery or fractionated stereotactic radiotherapy

• Malignant head and neck• Radical tumor with ICA sacrifice

When Is the Collateral Circulation Inadequate and Bypass Necessary?

• Anterior circulation• Posterior circulation• Distal arterial braches

Anterior circulation• Selective approach• angiographic evaluation of the competence of the circle of Willis• balloon test occlusion coupled with measurement of cerebral blood flow • patient pass balloon occlusion test : 20% chance of stroke with complete

occlusion without a bypass

• Universal approach• advocate bypass for all patients who undergo ICA occlusion

Posterior circulation

• Unclipable and uncoilable posterior circulation• Unilateral vertebral artery occlusion is well tolerated when • the contralateral vertebral artery is not hypoplastic• does not terminate in the posterior inferior cerebellar artery (PICA)

• Bilateral vertebral artery or basilar artery occlusion is associated with a much higher risk for ischemia and should be considered only if blood flow through both posterior communicating arteries is sufficient (>1 mm)

Distal arterial braches

• Proximal occlusion : ICA, VA• Occlusion of branch : MCA, PICA, AICA

Preoperative Planning and Preparation for Bypass Procedures

• Optimal site of arterial occlusion, the collateral circulation, and the size and location of the intended recipient and donor bypass vessels• Anticonvulsants• Aspirin (325 mg daily)

Intraoperative Monitoring and Management

• EEG : monitor burst suppression• Evoked potential : activity of the sensory cortex and subcortical and

brainstem pathways during bypass procedures• Mild hypothermic : 34-36 C• Thiopental : cerebral protection during transient focal ischemia• Local intraluminal anticoagulant irrigation is used• Do not use systemic heparin

Type of revascularization procedures

Interposition Vein Grafts

Extracranial-to-Intracranial Bypass with a Saphenous Vein Graft or Radial Artery Graft

Scalp Artery (Superficial Temporal or Occipital) Extracranial-to-Intracranial Bypass

Direct Intracranial Revascularization

Type I Bypasses—Interposition Vein Grafts

• Interposition graft from the parent artery proximal to the site of the occlusion to the point immediately distal to the parent artery• Purely intracranial petrous carotid–to–supraclinoid carotid saphenous

vein interposition graft• Remove skull base tumors and to treat giant intracavernous carotid

aneurysms• Disadvantage• Technically complex• Lengthy procedure• Prolonged period of ICA occlusion

Type II Bypasses—Extracranial-to-Intracranial Bypass with a Saphenous Vein Graft or Radial Artery Graft

• Extracranial Carotid Artery–to–Middle Cerebral Artery Saphenous Vein Interposition Graft• External Carotid Artery–to–Posterior Cerebral Artery Saphenous Vein

Interposition Graft

Type II Bypasses—Extracranial-to-Intracranial Bypass with a Saphenous Vein Graft or Radial Artery Graft• Normal blood flow MCA : 250 mL/min, PCA moderate less• STA graft position• 15-30 mL/min, may increase with time• not adequate to the circulation of major artery

• Saphenous vein graft• 70-140 mL/min,can exceed 250 mL/min, 4-5 mm• Lower longterm patency rate, higher risk of kinking, caliber mismatch

• Radial artery graft• Smaller diameter, 3.5 mm• 40-70 mL/min

Type II Bypasses—Extracranial-to-Intracranial Bypass with a Saphenous Vein Graft or Radial Artery Graft• Substiture for STA-MCA bypass• scalp artery is hypoplastic, diseased, or occluded• aneurysm that can be occluded only proximally, as in the case of some

dolichoectatic and fusiform aneurysms• type II bypass may supply too much flow and can be dangerous

Extracranial Carotid Artery–to–Middle Cerebral Artery Saphenous Vein Interposition Graft

External Carotid Artery–to–Posterior Cerebral Artery Saphenous Vein Interposition Graft

• Basilar artery or bilateral vertebral arteries are occluded to treat an unclippable basilar artery aneurysm• Subtemporal approach• The proximal 20 to 25 mm of the P2 segment is isolated, and a

segment free of brainstem perforating vessels is chosen for the anastomosis• Subdural hygroma : suggest routine subtemporal subdural-peritoneal

(or atrial) shunt

Type III Bypasses—Scalp Artery (Superficial Temporal or Occipital) Extracranial-to-Intracranial Bypass

• Used• a giant aneurysm requires occlusion of a single, crucial arterial branch • carotid occlusion is required (for an aneurysm or tumor) and the circle of

Willis is only marginally inadequate

• Donor vessel : STA, occipital artery• STA 15 – 30 mL/min• STA-PCA, STA-SCA• OA-PICA, OA-AICA

Superficial Temporal Artery–to–Middle Cerebral Artery Bypass

• Parietal branch : Charter’s point (center, 6 cm, above EAC)• Frontal branch : a second, vertically oriented incision above the ear is required

over Chater’s point

Superficial Temporal Artery–to–Middle Cerebral Artery Bypass• In patients who have two separate MCA branches that arise from the

dome of an aneurysm : double-barrel STA bypass• Recipient a. ,> 1 mm diameter, 10 mm length• Adventitia over the distal end of STA is removed• Off temporary clip : distal MCA, proximal MCA, STA

Occipital Artery–to–Posterior Inferior Cerebellar Artery Bypass

Superficial Temporal Artery–to–Superior Cerebellar Artery Bypass and Superficial Temporal Artery–to–Posterior Cerebral Artery Bypass

• Substituted for the saphenous vein graft–to-PCA bypass when some collateral blood flow is available through small posterior communicating arteries

Type IV Bypasses—Direct Intracranial Revascularization

• Anastomosis between two adjacent cerebral arteries• Primary Reanastomosis• intracranial arterial reconstruction involves excision of the aneurysm with

primary reconstruction of the parent artery

• Pericallosal-to-Pericallosal Bypass• used to treat fusiform aneurysms of the proximal pericallosal artery or for

giant anterior communicating artery aneurysms that require trapping• side-to-side anastomosis

Type IV Bypasses—Direct Intracranial Revascularization• Posterior Inferior Cerebellar Artery–to–Posterior Inferior Cerebellar

Artery Anastomosis• used when the occipital artery is small or has been damaged during a

previous surgical procedure• side-to-side anastomosis

Techniques for Occluding or Trapping an Aneurysm after Bypass

• Trapping• combined proximal and distal parent artery occlusion• it isolates the aneurysm from the circulation• avoids the risk of rupture from retrograde filling • allows immediate decompression of the aneurysm to relieve any mass effect.

• Proximal occlusion• induce aneurysmal thrombosis• Used in giant intracavernous aneurysms and large fusiform or dolichoectatic

vertebrobasilar aneurysms

Postoperative Management

• Palpating bypass pulse or by using a Doppler probe• Continue ASA• Euvolemia• Normal SBP• CTA

Complications• Early graft occlusion• careful avoidance of twisting, kinking, stretching, or tension of the graft• avoidance of graft spasm by adventitial papaverine irrigation• administration of perioperative antiplatelet therapy

• Post operative aneurysmal rupture• High flow graft• Emphasize the need to isolate the aneurysm completely from the circulation

by trapping whenever possible

Complications• Ischemic neurological deficits• Temporary arterial occlusion while the bypass anastomosis• Cerebral protection with moderate hypothermia, induced arterial

hypertension, and barbiturate administration

• Subdural or epidural hematomas (or both) developed postoperatively• given heparin in addition to aspirin

Long-Term Graft Patency

• Superior temporal artery graft• Radial artery graft• Saphenous vein graft