What cerebral artery territory is involved if there is weakness in both the right upper and lower extremities?

Left Middle Cerebral Artery (MCA) Territory

Weakness affecting both the right upper and lower extremities localizes to the left middle cerebral artery (MCA) territory, specifically involving the lateral motor cortex which contains motor representation for the contralateral face and upper extremity. 1

Anatomical Localization

The pattern of weakness you describe—affecting both right upper and lower extremities—indicates involvement of the left hemisphere motor cortex:

• The MCA supplies the lateral motor cortex, which contains motor representation for the contralateral face and upper extremity 1
• MCA strokes characteristically present with contralateral hemiparesis affecting the face and arm more than the leg, with sensory deficits following a similar distribution 1
• When both upper and lower extremities are equally affected, this suggests either a large MCA territory infarction or involvement of deeper structures like the internal capsule 2

Clinical Presentation Pattern

The typical MCA stroke presents with weakness that is more prominent in the face and arm compared to the leg 1, but when both upper and lower extremities show equal weakness, consider:

• Large superficial MCA territory infarction affecting multiple cortical areas 3
• Internal capsule involvement where descending motor fibers are tightly packed, causing equal upper and lower extremity weakness 2
• Combined cortical and subcortical involvement 2

Distinguishing from ACA Territory

This is critical to avoid misdiagnosis:

• ACA territory infarction characteristically causes contralateral weakness that is most prominent in the lower extremity 1
• The ACA supplies the medial motor cortex containing motor representation for the contralateral lower extremity 1
• If the leg were significantly weaker than the arm, you would suspect ACA territory involvement 1, 2

Imaging Considerations

CT imaging should be completed within 25 minutes of emergency department arrival with interpretation within an additional 20 minutes 4:

• Look for hyperdense MCA sign indicating thrombus or embolus in the first portion of the MCA 4
• Loss of gray-white differentiation in the cortical ribbon, particularly at the lateral margins of the insula or lentiform nucleus 4
• Sulcal effacement may be detected within 6 hours in up to 82% of patients with MCA territory ischemia 4
• Early infarct signs involving more than one-third of the MCA territory are associated with increased risk of hemorrhagic transformation following thrombolytic therapy 4

Common Pitfall

Do not confuse equal upper and lower extremity weakness with leg-predominant weakness—the latter would suggest ACA territory or parasagittal lesions 1, 2. The question specifically states both extremities are weak, which is the hallmark of MCA territory involvement when affecting the right side from a left hemisphere lesion 4, 1.