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Anterior cerebral artery (A3 Segment)

The A3 segment of the anterior cerebral artery (ACA), also known as the pericallosal artery, begins distal to the anterior communicating artery (AComA) and extends along the corpus callosum in the interhemispheric fissure. It runs superiorly and posteriorly, coursing over the genu of the corpus callosum, where it gives rise to multiple cortical branches.

The A3 segment supplies the medial frontal lobes, paracentral lobule, and anterior portions of the cingulate gyrus, areas essential for motor control of the lower limbs, cognition, and emotional regulation. It frequently anastomoses with contralateral ACA branches and with MCA cortical branches, contributing to cerebral collateral circulation.

Synonyms

  • Pericallosal artery

  • Distal ACA segment (post-communicating segment)

  • A3 segment of ACA

Function

  • Supplies blood to the medial frontal cortex, paracentral lobule, and cingulate gyrus

  • Provides perfusion to cortical areas responsible for motor function of the contralateral lower limb, executive function, and attention

  • Contributes to collateral flow via anastomoses with MCA and contralateral ACA branches

  • Maintains perfusion of the anterior corpus callosum

MRI Appearance

T1-weighted images (non-contrast):

  • Vessel lumen appears as a flow void (black signal) along the interhemispheric fissure

  • Surrounding white matter and corpus callosum appear as intermediate to high signal, helping delineate the artery’s course

T2-weighted images:

  • A3 segment demonstrates a flow void, consistent with fast-moving blood

  • Adjacent hyperintensity may indicate ischemia in ACA territory

MRA (Magnetic Resonance Angiography):

  • TOF and contrast-enhanced MRA depict the pericallosal artery’s origin, course over the corpus callosum, and cortical branches

  • Normal artery appears as a bright linear structure within the interhemispheric fissure

  • Useful for detecting stenosis, occlusion, aneurysm (particularly pericallosal aneurysms), or AVMs

T1 Post-Contrast (Gadolinium-enhanced MRI):

  • A3 lumen demonstrates intense enhancement

  • Enhancing cortical branches are visible along the medial frontal lobes and cingulate gyrus

  • Helps differentiate between vascular vs. non-vascular enhancing lesions in the interhemispheric fissure

CT Appearance

Non-contrast CT:

  • Artery not directly visible; may appear as a hyperdense artery sign if acutely thrombosed

  • Adjacent parenchymal infarcts in ACA territory can be inferred by hypodensity of medial frontal cortex or paracentral lobule

CT Angiography (CTA):

  • Clearly depicts the A3 segment as it courses over the genu of the corpus callosum

  • Shows relationship with the anterior communicating artery, A2, and distal cortical branches

  • Useful for evaluating aneurysms, stenosis, occlusions, AVMs, or surgical planning

MRI images

Anterior cerebral artery (A3 Segment) mri sagittal image -img-00000-00000

MRI images

Anterior cerebral artery (A3 Segment)