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Middle cerebral artery cortical segment (M4)

The middle cerebral artery (MCA) cortical segment (M4) refers to the terminal branches of the MCA after it emerges from the Sylvian fissure and reaches the cortical surface. These branches spread over the lateral convexity of the cerebral hemisphere, supplying the primary motor cortex, primary sensory cortex, frontal eye fields, language areas, and parietal association cortex, depending on the hemisphere and dominance.

The M4 segment includes numerous cortical branches, such as the precentral, central, anterior parietal, posterior parietal, angular, and temporal branches. These arteries form rich pial anastomoses with branches of the anterior cerebral artery (ACA) and posterior cerebral artery (PCA), providing collateral circulation in cases of vascular compromise.

Synonyms

  • MCA cortical branches

  • Distal MCA segment

  • Terminal branches of MCA

  • M4 MCA segment

Function

  • Supplies blood to the lateral surface of the frontal, parietal, and temporal lobes

  • Perfuses eloquent cortical areas, including motor, sensory, and speech regions

  • Provides collateral circulation through anastomoses with ACA and PCA cortical branches

  • Maintains higher-order brain functions such as language, motor control, and spatial integration

MRI Appearance

T1-weighted images (non-contrast):

  • M4 cortical branches appear as linear flow voids along cortical sulci

  • Not well visualized without angiographic sequences

T2-weighted images:

  • Also demonstrate flow voids from fast arterial blood flow

  • Abnormal hyperintensity in adjacent cortex may indicate ischemia, infarction, or cortical edema

MRA (Magnetic Resonance Angiography):

  • TOF and contrast-enhanced MRA clearly demonstrate the branching pattern of M4 arteries over the cortical convexity

  • Appear as bright, enhancing vessels extending across the cortical surface

  • Useful for detecting stenosis, occlusion, aneurysm, or AVM involving cortical branches

T1 Post-Contrast (Gadolinium-enhanced MRI):

  • Enhances arterial lumen and helps visualize small cortical branches not seen on routine sequences

  • Highlights abnormal vascular patterns in tumor neovascularity or vascular malformations

CT Appearance

Non-contrast CT:

  • M4 branches are usually not visible, but acute thrombus may appear as a hyperdense cortical artery sign

  • Infarction in M4 territories presents as cortical hypodensity with sulcal effacement

CT Angiography (CTA):

  • Clearly visualizes the distal MCA cortical branches over the lateral hemispheric convexity

  • Opacified arteries are traced to their cortical distribution, enabling precise evaluation of stenosis, occlusion, aneurysm, or AVM

  • Essential for stroke assessment, surgical planning, and cortical vascular mapping

MRI images

Middle cerebral artery cortical segment (M4)