MICROANATOMY OF THE ANTERIOR PORTION OF CIRCLE OF WILLIS / 解剖学报

ABSTRACT

The anterior portion of the circle of Willis was examined in 106 adult and child brains under 6～40 magnifications. In this study,the proximal portion of the left anterior cerebral artery(A_1 segment) was larger and shorter than that of the right.The hypoplastic A_1 were found in 8.49?1.91%,mostly on the right side.In approximately 50% cases,A_1 were curved in their courses.A_1 passed across the optic nerve or optic chiasma to the longitudinal fissure where they communicated with the opposite ant.cereb,art.by the short anterior communicating artery(AGOA)lying in front of the optic chiasma(56.19?4.74%). In most of the cases,the recurrent artery belonged to one-branch type or two-branch type.It arose from the ant.cereb,art.at the level of the AGOA in 52.53?2.89%, usually coursing anterior to A_1 segment.This artery had many perforating branches (average 4.5)which perforated into the ant.perforated substance.Some of these branches may be traced to the inf.surface of frontal lobe,the olfactory sulcus,Sylvian fissure and suprachiasmatic area. In most cases,the anterior perforating artery belonged to one-branch type or two- branch type too,most frequently arising from the lat.portion of A_1.It was usually divided into perforating branches to the ant.perforated substance.Some of them may be traced to the olfactory tract,olfactory trigone,gyrus rectus,subcallosal gyrus and optic chiasma. The hypothalamic branches mainly arose from the lat.portion of A_1.The average number was 8.6.These branches may be traced to the optic tract,the dorsal surface of the optic chiasma,the ant.perforated substance,subcallosal gyrus and the genu of corpus callosum. The AGOA had many variations.In this study,the normal type was seen in 43.39 ?4.71%.The AGOA frequently gave rise to perforating arteries terminating in the suprachiasmatic area,the dorsal surface of the optic chiasma,lamina terminalis,subcal- losal gyrus,and the septic area.The number of perforating branches ranged from 1～8 (average 4.7).The frequent variations such as double or triple branches were encoun- tered. The third or median ant.cereb,art.arising from the ACOA was found in 17 cases (16.0?3.5%).Most of them were small and short,while only a few were large and coursing upward and backward over the dorsum of corpus callosum,and gave branches to the anteriomedial surface of the hemisphere.