| Objective: The aim of this study is to research on the microanatomical structure of the M1 segment of MCA, the surface projection of the bifurcation of M1, and the relationship between the M1 bifurcation and the superficial sylvian veins. It offers reference data and space quantification concepts for operations operated trough lateral fissure.Methods: On 30 samples of adult heads fixed with formaldehyde solution, we use red latex to pour into the bilateral internal carotids and vertebral arteries, and undertake pterion approach from the left and right separately. We undertake microanatomy on the M1 segment of the MCA under a microscope, and measure the distance between the middle of the M1 segment and the anterior wall of the sphenoidal crest, the length and diameter of the M1 segment, and the numbers and types of the lenticulostriate arteries and cortical arteries of the M1 segment. We set a coordinate axe on the samples which takes the horizontal line from the infraorbital margin to the upper edge of the external acoustic pore as the x-axis, and the line going through the frontal edge of the external acoustic pore vertical to the x-axis as the y-axis (the number below the x-axis is positive while under is negative, and the number before the y-axis is positive while after is negative), and measure the number of the projection of the M1 bifurcation on this coordinate. We observe the relationships between the M1 bifurcation and the superficial sylvian veins under different head positions, and measure the vertical distance between them. The numbers we get undergo statistical analysis with the SPSS16.0 software.Results: The M1 segment of the MAC lies in the sphenoidal crest, with most of it below the height of the sphenoidal ridge and partly equal to it. The distance between the middle of the M1 segment and the anterior wall of the sphenoidal crest is:left: 3.94士0.36mm; right: 3.91士0.23mm. The length of the M1 segment is: left: 18.30士3.06mm;right: 18.01士2.44mm. The diameter is:left: 3.60士0.49mm; right: 3.57士0.50mm. The branches of the M1 segment are divided into the lenticulostriate arteries and cortical arteries. The numbers of the lenticulostriate arteries are: left: 8.27士2.49;right: 7.67士2.35.There are all together 21 branches of cortical arteries, including 12 temporal poles (57.14%) , 5 frontal temporal arteries (23.81%), 2 prefrontal orbital arteries and 2 prefrontal arteries (9.52% each). There are 26 samples of double type of M1 segment (86.67%), 4 samples of triple type and no single type is found. There is one sample of M1 segment that has a variation of complex type of MCA (3.33%), and no accessory MCA is found. The projection of the M1 bifurcation is:X-axis of the left: 26.56士3.03mm;Y-axis of the left: 46.71士4.24mm;X-axis of the right: 27.03士2.92mm;Y-axis of the right: 45.48士4.20mm.When the head is turned by 30°toward the other side, the M1 bifurcations all lie in the lateral of the superficial sylvian veins , and when turned by 60°, there are 4 samples that lie in the left and 5 samples in the right of the lateral of the superficial sylvian veins , and the rest all lie below the superficial sylvian veins. The vertical distance between the M1 bifurcation and the superficial sylvian vein is:left: 14.60士2.27mm;right: 15.03士2.36mm.Conclusions: 1 The M1 segment of the MCA goes nearby the back wall of the sphenoidal cyst. The distance between the middle of the M1 segment and the frontal wall of the sphenoidal crest is:left: 3.94士0.36mm;right: 3.91士0.23mm.The variations of the M1 segment are multivariate, so when separating the lateral fissure, we should operate as close as possible to the frontal wall of it, and observe carefully during the operation to avoid injuries. 2 The real bifurcation of the M1 segment always lies on the top of the limen of insula. In a circular range with a center located at X=25.0mm and Y=45.0mm, and a radius of 10mm, there are 27 samples of projections of M1 segment (90.00%).3 The relationship between the M1 bifurcation and the superficial sylvian vein is closely related to the head position. When the head is turned by 30°toward the other side, the M1 bifurcations all lie in the lateral of the superficial sylvian veins, and when turned by 60°, there are 9 samples that lie in the lateral of the superficial sylvian veins, and the rest 21 samples all lie below the superficial sylvian veins.
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