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Middle cerebral artery insular segment (M2)

The insular segment (M2) of the middle cerebral artery (MCA) begins at the point where the MCA emerges from the sylvian (lateral) fissure after the horizontal sphenoidal (M1) segment. The M2 segment courses superiorly and posteriorly over the insula, giving rise to multiple insular and opercular branches before continuing into the opercular (M3) segment.

M2 branches supply the insular cortex, lateral basal ganglia regions, and adjacent opercular areas. Through its cortical branches, the M2 segment contributes significantly to perfusion of the frontal, parietal, and temporal opercula, as well as collateral supply via anastomoses with anterior and posterior cerebral arteries.

Synonyms

  • Insular segment of MCA

  • M2 segment of MCA

  • MCA insular artery

Function

  • Provides blood supply to the insula and opercular regions

  • Contributes to perfusion of language, auditory, and sensory integration areas

  • Serves as a critical vascular segment for stroke localization and endovascular procedures

  • Forms part of the collateral circulation with adjacent MCA, ACA, and PCA territories

MRI Appearance

T1-weighted images (non-contrast):

  • M2 segment vessels appear as flow voids (signal loss) within the sylvian fissure

  • Insular cortex and opercular brain parenchyma are clearly delineated

T2-weighted images:

  • Vessels remain flow voids

  • Hyperintense signal in surrounding parenchyma may suggest ischemia or edema in M2 vascular territory

MRA (Magnetic Resonance Angiography):

  • TOF and contrast-enhanced MRA depict the origin, branching, and course of the M2 segment along the insula

  • Appears as a bright, enhancing lumen on angiographic images

  • Useful for detecting stenosis, occlusion, aneurysm, or AVM involving the insular MCA branches

T1 Post-Contrast (Gadolinium-enhanced MRI):

  • Demonstrates strong enhancement of M2 lumen

  • Enhances visualization of small insular branches

  • Useful for evaluating vascular malformations or collateral vessels

CT Appearance

Non-contrast CT:

  • M2 segment not directly seen unless abnormal (hyperdense MCA sign in acute thrombus)

  • Indirect findings include loss of insular ribbon sign, an early ischemic change in M2 infarction

CT Angiography (CTA):

  • Clearly demonstrates the MCA bifurcation, M2 origin, course over the insula, and opercular branches

  • Excellent for evaluating stenosis, occlusion, aneurysms, and collateral flow

  • Gold standard in stroke imaging, surgical planning, and endovascular interventions

MRI images

Middle cerebral artery insular segment (M2)