middle cerebral artery

**Anatomy** - Origin: terminal branch of the internal carotid artery (ICA), along with the anterior cerebral artery (ACA), at the carotid terminus. - Segments: M1 (sphenoidal/horizontal), M2 (insular), M3 (opercular), M4 (cortical). - M1 gives off the lenticulostriate arteries. These are small penetrating end-arteries that supply the putamen, globus pallidus (lateral part), caudate (body), and the posterior limb of the internal capsule. They are prone to lacunar infarcts in chronic hypertension (lipohyalinosis). - M2 divides into a superior division and an inferior division. - Superior division: lateral frontal lobe, including Broca area, the motor and sensory cortex for the face and arm, and the frontal eye field. - Inferior division: lateral temporal and inferior parietal lobes, including Wernicke area, the angular gyrus, and the optic radiations (Meyer loop).

**Territory** - Lateral convexity of the frontal, parietal, and temporal lobes. - Primary motor (precentral gyrus) and somatosensory (postcentral gyrus) cortex for the face and upper limb. The leg area is supplied by the ACA, which is why leg involvement is less prominent.

**Clinical presentation of MCA stroke** - Contralateral hemiparesis and sensory loss, with face and arm worse than leg. - Dominant hemisphere (usually left): - Broca (expressive) aphasia: nonfluent speech with intact comprehension, from a superior division lesion. - Wernicke (receptive) aphasia: fluent but nonsensical speech with impaired comprehension, from an inferior division lesion. - Global aphasia if the whole territory is involved. - Gerstmann syndrome (angular gyrus): agraphia, acalculia, finger agnosia, left-right confusion. - Non-dominant hemisphere (usually right): - Hemispatial neglect, anosognosia, and apraxia (for example, dressing apraxia). Contralateral neglect is typical of right parietal lesions. - Aprosodia. - Contralateral homonymous hemianopia (often with inferior quadrantanopia from parietal optic radiation involvement, "pie in the sky" superior quadrantanopia from temporal Meyer loop involvement). - Gaze preference toward the side of the lesion (frontal eye field damage). The eyes look toward the lesion and away from the hemiparesis.

**Key associations and clinical pearls** - Most common site of ischemic stroke, often from cardioembolism (atrial fibrillation) or artery-to-artery embolism from the carotid, because the MCA is a direct continuation of the ICA. - Hyperdense MCA sign on noncontrast CT indicates acute thrombus or embolus in the vessel. - "Malignant MCA infarction": a large territory infarct causes massive cerebral edema, midline shift, and risk of herniation. Treat with decompressive hemicraniectomy in selected patients. - Lenticulostriate occlusion causes a pure motor lacunar stroke (posterior limb of the internal capsule), with contralateral face, arm, and leg weakness and no cortical signs. - Mycotic aneurysms and berry aneurysms can occur at the MCA bifurcation. The MCA is the third most common site of berry aneurysm after the ACom/ACA and the PCom. - Management of acute ischemic stroke: noncontrast CT to exclude hemorrhage, IV thrombolysis (alteplase or tenecteplase) within 4.5 hours of onset if there are no contraindications, and mechanical thrombectomy for large vessel occlusion (including proximal MCA M1 and sometimes M2) up to 24 hours in selected patients with favorable imaging. Secondary prevention includes antiplatelets, statins, blood pressure control, and anticoagulation for atrial fibrillation.

**Mnemonic** - MCA: "Motor Cortex Arm and face" (and language). - ACA stroke: leg weakness greater than arm, with abulia and urinary incontinence. - PCA stroke: contralateral homonymous hemianopia with macular sparing.