Anterior cerebral artery
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The anterior cerebral artery (ACA), along with the middle cerebral artery (MCA) forms at the termination of the internal carotid artery (ICA). It is the smaller of the two and arches anteromedially to pass anterior to the genu of the corpus callosum, dividing as it does so into its two major branches: the pericallosal and callosomarginal arteries.
It supplies the medial aspect of the cerebral hemispheres back to the parietal lobe.
origin: termination of the internal carotid artery
course: from the medial end of the lateral fissure stem to the corpus callosum
supply: the corpus callosum, the septum pellucidum, the putamen (anterior portion), the head of the caudate nucleus, and parts of the internal capsule
The anterior cerebral artery is divided into five segments 8-10:
A1: horizontal or pre-communicating segment
A2: vertical, post-communicating or infracallosal segment
terminates either at the junction of the rostrum and genu of the corpus callosum at the apex of the dorsal convex arch, or at the origin of the callosomarginal artery
A3: precallosal segment
extends around the genu of the corpus callosum, or originates distal to the origin of the callosomarginal artery
terminates where the artery turns directly posterior above the corpus callosum
A4: supracallosal segment
above the body of the corpus callosum anterior to the plane of the coronal suture
A5: postcallosal segment
above the body of the corpus callosum posterior to the plane of the coronal suture
The pericallosal artery refers either to the distal part of the ACA starting from A2 (after the origin of the anterior communicating artery) or from A3 (defined after the origin of the callosomarginal artery). In the former case, the A2, A3, and A4-5 segments refer to proximal, middle, and distal segments of the pericallosal artery, respectively 11,12.
The A4 and A5 segments predominantly run along the callosal sulcus, but in a minority of cases run above that, medial to the cingulate gyrus.
There are two main branching patterns of the anterior cerebral artery. In the first, the A2 gives off the callosomarginal artery (which lies in the cingulate sulcus) and continues as the pericallosal artery. In this configuration, the terminal (cortical) branches arise from the callosomarginal artery.
In the second configuration, the callosomarginal artery is absent and the terminal branches arise directly from the pericallosal artery.
Terminal (cortical) branches
Orbital branches, 2 or 3 in number, branch over the orbital surface of the frontal lobe supplying:
They are named:
Frontal branches supply:
corpus callosum (with the exception of the splenium)
paracentral lobule (as the branches reach over the vertex to supply a strip of cortex on the surface, they are responsible for supply to the lower limbs)
Parietal branches supply:
Multiple small branches are given off proximally (A1, ACom, proximal A2) supply:
rostrum of the corpus callosum
anterior part of the putamen
head of the caudate nucleus
anteromedial part of the anterior limb of the internal capsule
The latter two - head of caudate and adjacent part of the internal capsule - are supplied by the recurrent artery of Heubner and associated smaller perforating branches. It has its origin near the A1-ACom-A2 junction and can arise from all three, although usually, it is from the A2. It curves back on itself and is at risk of ACom aneurysm clipping.
ACA fenestration with a reported incidence of 0-4% of A1 segment fenestration
azygos ACA: ACA territories supplied by a single A2 trunk; incidence of ~2% (range 0.2-4%)
ACA trifurcation: three A2 segments; incidence of ~7.5% (range 2-13%)
bihemispheric ACA: a hypoplastic A2 segment with contralateral A2 segment dominance supplying both ACA territories; incidence of ~4.5% (range 2-7%)
A1 segment absence/hypoplasia, contralateral A1 segment dominance and supply to ipsilateral A2 segment by a large anterior communicating artery: 10% of individuals demonstrate hypoplasia of A1 segment using a diameter 1.5 mm or smaller
duplication of A1
two or three anterior communicating arteries
asymmetry of A1 segment which is associated with ACA aneurysm
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