Anterior cerebral artery

The anterior cerebral artery along with the middle cerebral artery, forms at the termination of the internal carotid artery. It is the smaller of the two, and arches antro-medially to pass anterior to genu of the corpus callosum, dividing as it does so into its two major branches; pericallosal and callosomarginal arteries (see below). 

It supplies the medial aspect of the cerebral hemispheres back to the parietal lobe. 

Segments

The ACA is divided into three segments:

• A1 : origin from the ICA to the anterior communicating artery (ACOM). ~ 14mm in length.
• A2 : from ACOM to the origin of the callosomarginal artery
• A3 : distal to the origin of the callosomarginal artery  (aka pericallosal artery)

Branches

There are two main branching patterns of the ACA. 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 are given off the callosomarginal artery.

In the second configuration the callosomarginal is absent and the terminal branches arise directly from the pericallosal.

Terminal (cortical) branches

Orbital branches, 2 or 3 in number, branch over the orbital surface of the frontal lobe supplying:

• olfactory cortex
• gyrus rectus
• medial orbital gyrus

They are named:

• medial frontobasal artery
• polar frontal artery

Frontal branches supply:

• corpus callosum (with the exception of the splenium)
  • pericallosal artery
• cingulate gyrus
• medial frontal gyrus
• paracentral lobule (as the branches reach over the vertex to supply a stip of cortex on the surface, they are responsible for supply to the lower limbs)

Parietal branches supply :

• precuneus

Central branches

Multiple small branches given off proximally (A1, ACOM, proximal A2) supply:

• anterior perforated substance
• lamina terminalis
• rostrum of the corpus callosum
• septum pellucidum
• 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 from ACOM aneurysm clipping.