Microvascular bypass surgery Part 1: Anatomical studies
NORMAN CHATER, M.D., ROnERT SPETZLER, M.D., KENT TONNEMACHER, B.S., AND CHARLES B. WILSON, M.D. Department of Neurological Surgery, University of California School of Medicine, and the Ralph K. Davies Medical Center, San Francisco, California ua Microvascular anatomical studies were performed to ascertain the most suitable cortical vessel for extracranial-intracranial arterial bypass (EIAB). The three most commonly used cortical areas (the tip of the frontal lobe, the tip of the temporal lobe, and the area at the angular gyrus) were examined in detail. Because of their accessibility and size, the cortical arteries in the area of the angular gyrus offer the most suitable location for creating an EIAB. KEY WORDS 9 extracraniai-intracranial arterial bypass 9 superficial temporal artery 9 middle cerebral artery anastomosis revascnlarization 9 transient ischemic attacks
p
IONEERING studies by Donaghy, 4 and Ya~argil, et a1.,1~'13 suggest that microvascular bypass surgery may benefit patients suffering from transient ischemic attacks (TIA's) due to occlusive cerebrovascular lesions. Theoretically, microvascular anastomosis gives ischemic cortex an additional collateral blood supply. Provisional indications for such a surgical procedure have been described elsewhere. 2'3 In many cases TIA's and strokes are caused by emboli in the territory irrigated by the middle cerebral artery (MCA). According to the principles of laminar flow, emboli tend to be channeled into the middle region of the internal carotid artery (ICA) and, as a result, are carried primarily through the relatively 7"12
large orifice of the MCA as it branches off the ICA. Symptomatic occlusive intracranial vascular disease of nonembolic origin also affects the MCA tree. Chronic complete occlusion of the cervical internal carotid artery frequently causes symptoms referable to the MCA distribution; standard endarterectomy is not recommended for this lesion because of poor postoperative patency rates.l.5,9 ix In this paper we report on the technical and anatomical factors important in establishing optimal flow and, consequently, an efficient extra-intracranial artery bypass (EIAB). If the EIAB is to be effective in establishing a collateral blood supply to ischemic cortex, the extracranial artery must be anastomosed to J. Neurosurg. / Volume 44 / June, 1976
M i c r o v a s c u l a r [)}'pass s u r g e r y some portion of the MCA tree and provide sufficient blood flow to support adequate metabolic function. The cortical branches of the MCA are readily accessible anatomically by means of a small craniectomy, and in order to determine which branch of the MCA is best suited to microvascular anastomosis, we undertook a detailed topographical analysis of the superficial cortical vasculature. The parameters recorded in this study were vessel size, location, and accessibility. M a t e r i a l s and M e t h o d s
Fifty cadaver brains were injected with latex and fixed in formalin. ~ The surface arterial vasculature of three cortical regions, namely, the convexity of the frontal lobe, the tip of the temporal lobe, and the region of the angular gyrus (the sites most commonly used for EIAB), were observed with the operating microscope (Fig. 1). The course and size of the superficial cortical vasculature were recorded. A 4-cm cortical zone (Fig. 2) representative of the exposure obtained through a small craniectomy was examined in the tip of the temporal lobe, the frontal lobe, and the area of the angular gyrus.
FIG. 1. View through the operating microscope of the latex-injected angular gyrus branch of the middle cerebral artery.
Results
Marked variations in size of the surface cortical arteries were apparent upon microscopic examination. The surface arteries at the tip of the angular gyrus were consistently larger than the arteries of the other two regions observed. The results are summarized in Table 1. Discussion
In determining the cortical arteries best suited for microvascular anastomosis we con-
FIG. 2. Diagram showing the three 4-cm cortical zones studied for microvascular detail.
TABLE 1 Cortical artery diameter measurements in 50 cadavers
Cortical Artery Diameter (ram) >_2.0 mm >_1.8 mm >- 1.4 mm >-1.0 mm* >_0.9 mm >-0.6 mm
Tip of Temporal Lobe ( ~ incidence)
Frontal Lobe ( ~ incidence)
5 5
0 5
70 100
52 63 100
17
5
AngularGyrus Temporal Lobe ( ~ incidence) 35 57
100
* Critical diameter for long-term patency. J. Neurosurg. / Volume 44 / June, 1976
713
N. C h a t e r , et al. attacks. J Neurol Neurosurg Psychiatry sidered three factors, namely, consistent 28:533-539, 1965 topography, external diameter, and proximity 2. Chater N, Mani J, Tonnemacher K: Superto superficial temporal artery and occipital ficial temporal artery bypass in occlusive artery. The availability of a suitable artery cerebral vascular disease. Calif Med 119:9-13, did not prove to be a discriminating factor August 1973 because all three cortical regions consistently 3. Chater N, Spetzler R, Mani J: The spectrum contained one or more acceptable arteries of cerebrovascular occlusive disease suitable within the designated 4-cm zone. for microvascular bypass surgery. Angiology 26:235-251, 1975 Other factors being equal, the size of the 4. Donaghy RMP: What's new in surgery? lumen determines flow through a conduit. Neurological surgery. Surg Gynecoi Obstet According to Poiseuille's law, which states 134:269-271, 1972 that flow is directly proportional to the fourth 5. Fields WS, North RR, Hass WK, et al: Joint power of the radius when all other factors restudy of extracranial arterial occlusion as a main constant, a diameter reduction of 50%, cause of stroke. 1. Organization of study and that is, from a 2-ram to a l-ram lumen, will survey of patient population. JAMA 203: result in a 16-fold reduction in flow. Although 955-960, 1968 the principles defining flow of a Newtonian 6. Leighton RS: Neuroradiologic Anatomy: A fluid through a rigid cylinder are not strictly Stereoscopic Atlas. Baltimore: Williams & Wilkins, 1971, pp 5-7 applicable to the complex laminar flow char7. Spetzler R, Chater N: Occipital artery-middle acteristics of a pulsatile circulatory system, cerebral artery anastomosis for cerebral artery this model provides a reasonable approximaocclusive disease. Surg Neorol 2:235-238, tion of changes that may occur in circulation 1974 when various flow parameters are altered. 8. Szilyagi DE, Whitcomb JG, Schenker W, et As indicated in Table 1, the largest cortical al: The laws of fluid flow and arterial grafting. arteries course over the angular gyrus, and it Surgery 47:55-73, 1960 is the only cortical area consistently con9. Thompson JE, Austin DJ, Patman RD: Endtaining superficial arteries with a diameter arterectomy of the totally occluded carotid greater than 1 ram. A diameter of 1 mm apartery for stroke. Results in 100 operations. Arch Surg 95:791-799, 1967 proaches the minimum critical diameter required for long-term anastomotic patency. 2,s 10. Toole JF, Janeway R, Choi K, et al: Transient ischemic attacks due to atherosclerosis. A In contrast, arteries available at the tip of the prospective study of 160 patients. Arch Neuroi temporal lobe and over the frontal convexity 32:5-12, 1975 are considerably smaller than those of the 11. Wylie EJ, Hein MF, Adams JE: Intracranial angular gyrus region, and these two regions hemorrhage following revascularization for satisfy the l-ram critical diameter requiretreatment of acute strokes. J Neurosurg ment only 70% and 52% of the time respec21:212-215, 1964 tively. 12. Yasargil MG: Microsurgery Applied to A second advantage of the cortical vessels Neurosurgery. Stuttgart: Georg Thieme, 1969, pp 105-117 in the region of the angular gyrus is their proximity to either the dissected superficial 13. Yasargil MG, Krayenbfihl HA, Jacobson JH 2nd: Microneurosurgical arterial reconstructemporal artery or the occipital artery. 6'7 In tion. Surgery 67:221-233, 1970 contrast, the use of temporal and frontal arteries, because of their rostral location, would impose significant tension on the occipital artery. The present study indicates that the superficial arteries of the angular gyrus, This paper was presented in part at the Interfor instance the posterior temporal artery or national Congress of Neurological Surgery, at the angular artery, are most suitable for Kyoto, Japan, in September, 1973. This work was supported in part by NINCDS EIAB. We have also shown that with a high Training Grant 5593. degree of probability, a 4-cm craniectomy Present address for Dr. Chater: Ralph K. Davies over this region will expose these arteries. Medical Center, San Francisco, California. Address reprint requests to." Editorial Office, References Department of Neurological Surgery, University 1. Burrows EH, Marshall J: Angiographic in- of California School of Medicine, San Francisco, vestigation of patients with transient ischemic California 94143. 71,4
J. Neurosurg. / Volume 44 / June, 1976
NORMAN CHATER, M.D., ROnERT SPETZLER, M.D., KENT TONNEMACHER, B.S., AND CHARLES B. WILSON, M.D. Department of Neurological Surgery, University of California School of Medicine, and the Ralph K. Davies Medical Center, San Francisco, California ua Microvascular anatomical studies were performed to ascertain the most suitable cortical vessel for extracranial-intracranial arterial bypass (EIAB). The three most commonly used cortical areas (the tip of the frontal lobe, the tip of the temporal lobe, and the area at the angular gyrus) were examined in detail. Because of their accessibility and size, the cortical arteries in the area of the angular gyrus offer the most suitable location for creating an EIAB. KEY WORDS 9 extracraniai-intracranial arterial bypass 9 superficial temporal artery 9 middle cerebral artery anastomosis revascnlarization 9 transient ischemic attacks
p
IONEERING studies by Donaghy, 4 and Ya~argil, et a1.,1~'13 suggest that microvascular bypass surgery may benefit patients suffering from transient ischemic attacks (TIA's) due to occlusive cerebrovascular lesions. Theoretically, microvascular anastomosis gives ischemic cortex an additional collateral blood supply. Provisional indications for such a surgical procedure have been described elsewhere. 2'3 In many cases TIA's and strokes are caused by emboli in the territory irrigated by the middle cerebral artery (MCA). According to the principles of laminar flow, emboli tend to be channeled into the middle region of the internal carotid artery (ICA) and, as a result, are carried primarily through the relatively 7"12
large orifice of the MCA as it branches off the ICA. Symptomatic occlusive intracranial vascular disease of nonembolic origin also affects the MCA tree. Chronic complete occlusion of the cervical internal carotid artery frequently causes symptoms referable to the MCA distribution; standard endarterectomy is not recommended for this lesion because of poor postoperative patency rates.l.5,9 ix In this paper we report on the technical and anatomical factors important in establishing optimal flow and, consequently, an efficient extra-intracranial artery bypass (EIAB). If the EIAB is to be effective in establishing a collateral blood supply to ischemic cortex, the extracranial artery must be anastomosed to J. Neurosurg. / Volume 44 / June, 1976
M i c r o v a s c u l a r [)}'pass s u r g e r y some portion of the MCA tree and provide sufficient blood flow to support adequate metabolic function. The cortical branches of the MCA are readily accessible anatomically by means of a small craniectomy, and in order to determine which branch of the MCA is best suited to microvascular anastomosis, we undertook a detailed topographical analysis of the superficial cortical vasculature. The parameters recorded in this study were vessel size, location, and accessibility. M a t e r i a l s and M e t h o d s
Fifty cadaver brains were injected with latex and fixed in formalin. ~ The surface arterial vasculature of three cortical regions, namely, the convexity of the frontal lobe, the tip of the temporal lobe, and the region of the angular gyrus (the sites most commonly used for EIAB), were observed with the operating microscope (Fig. 1). The course and size of the superficial cortical vasculature were recorded. A 4-cm cortical zone (Fig. 2) representative of the exposure obtained through a small craniectomy was examined in the tip of the temporal lobe, the frontal lobe, and the area of the angular gyrus.
FIG. 1. View through the operating microscope of the latex-injected angular gyrus branch of the middle cerebral artery.
Results
Marked variations in size of the surface cortical arteries were apparent upon microscopic examination. The surface arteries at the tip of the angular gyrus were consistently larger than the arteries of the other two regions observed. The results are summarized in Table 1. Discussion
In determining the cortical arteries best suited for microvascular anastomosis we con-
FIG. 2. Diagram showing the three 4-cm cortical zones studied for microvascular detail.
TABLE 1 Cortical artery diameter measurements in 50 cadavers
Cortical Artery Diameter (ram) >_2.0 mm >_1.8 mm >- 1.4 mm >-1.0 mm* >_0.9 mm >-0.6 mm
Tip of Temporal Lobe ( ~ incidence)
Frontal Lobe ( ~ incidence)
5 5
0 5
70 100
52 63 100
17
5
AngularGyrus Temporal Lobe ( ~ incidence) 35 57
100
* Critical diameter for long-term patency. J. Neurosurg. / Volume 44 / June, 1976
713
N. C h a t e r , et al. attacks. J Neurol Neurosurg Psychiatry sidered three factors, namely, consistent 28:533-539, 1965 topography, external diameter, and proximity 2. Chater N, Mani J, Tonnemacher K: Superto superficial temporal artery and occipital ficial temporal artery bypass in occlusive artery. The availability of a suitable artery cerebral vascular disease. Calif Med 119:9-13, did not prove to be a discriminating factor August 1973 because all three cortical regions consistently 3. Chater N, Spetzler R, Mani J: The spectrum contained one or more acceptable arteries of cerebrovascular occlusive disease suitable within the designated 4-cm zone. for microvascular bypass surgery. Angiology 26:235-251, 1975 Other factors being equal, the size of the 4. Donaghy RMP: What's new in surgery? lumen determines flow through a conduit. Neurological surgery. Surg Gynecoi Obstet According to Poiseuille's law, which states 134:269-271, 1972 that flow is directly proportional to the fourth 5. Fields WS, North RR, Hass WK, et al: Joint power of the radius when all other factors restudy of extracranial arterial occlusion as a main constant, a diameter reduction of 50%, cause of stroke. 1. Organization of study and that is, from a 2-ram to a l-ram lumen, will survey of patient population. JAMA 203: result in a 16-fold reduction in flow. Although 955-960, 1968 the principles defining flow of a Newtonian 6. Leighton RS: Neuroradiologic Anatomy: A fluid through a rigid cylinder are not strictly Stereoscopic Atlas. Baltimore: Williams & Wilkins, 1971, pp 5-7 applicable to the complex laminar flow char7. Spetzler R, Chater N: Occipital artery-middle acteristics of a pulsatile circulatory system, cerebral artery anastomosis for cerebral artery this model provides a reasonable approximaocclusive disease. Surg Neorol 2:235-238, tion of changes that may occur in circulation 1974 when various flow parameters are altered. 8. Szilyagi DE, Whitcomb JG, Schenker W, et As indicated in Table 1, the largest cortical al: The laws of fluid flow and arterial grafting. arteries course over the angular gyrus, and it Surgery 47:55-73, 1960 is the only cortical area consistently con9. Thompson JE, Austin DJ, Patman RD: Endtaining superficial arteries with a diameter arterectomy of the totally occluded carotid greater than 1 ram. A diameter of 1 mm apartery for stroke. Results in 100 operations. Arch Surg 95:791-799, 1967 proaches the minimum critical diameter required for long-term anastomotic patency. 2,s 10. Toole JF, Janeway R, Choi K, et al: Transient ischemic attacks due to atherosclerosis. A In contrast, arteries available at the tip of the prospective study of 160 patients. Arch Neuroi temporal lobe and over the frontal convexity 32:5-12, 1975 are considerably smaller than those of the 11. Wylie EJ, Hein MF, Adams JE: Intracranial angular gyrus region, and these two regions hemorrhage following revascularization for satisfy the l-ram critical diameter requiretreatment of acute strokes. J Neurosurg ment only 70% and 52% of the time respec21:212-215, 1964 tively. 12. Yasargil MG: Microsurgery Applied to A second advantage of the cortical vessels Neurosurgery. Stuttgart: Georg Thieme, 1969, pp 105-117 in the region of the angular gyrus is their proximity to either the dissected superficial 13. Yasargil MG, Krayenbfihl HA, Jacobson JH 2nd: Microneurosurgical arterial reconstructemporal artery or the occipital artery. 6'7 In tion. Surgery 67:221-233, 1970 contrast, the use of temporal and frontal arteries, because of their rostral location, would impose significant tension on the occipital artery. The present study indicates that the superficial arteries of the angular gyrus, This paper was presented in part at the Interfor instance the posterior temporal artery or national Congress of Neurological Surgery, at the angular artery, are most suitable for Kyoto, Japan, in September, 1973. This work was supported in part by NINCDS EIAB. We have also shown that with a high Training Grant 5593. degree of probability, a 4-cm craniectomy Present address for Dr. Chater: Ralph K. Davies over this region will expose these arteries. Medical Center, San Francisco, California. Address reprint requests to." Editorial Office, References Department of Neurological Surgery, University 1. Burrows EH, Marshall J: Angiographic in- of California School of Medicine, San Francisco, vestigation of patients with transient ischemic California 94143. 71,4
J. Neurosurg. / Volume 44 / June, 1976
