Following a cardiac arrest, a 60-year-old man regains consciousness but has bilateral weakness predominantly affecting the proximal arms and legs, with relative sparing of the face. MRI shows symmetric infarction in the parasagittal parietal regions. These lesions represent:

• A Embolic infarcts in the territory of the posterior cerebral arteries
• B Border zone infarcts between the anterior and middle cerebral artery territories ✓
• C Venous infarcts of the superior sagittal sinus
• D Lacunar infarcts of the internal capsule

Explanation

The parasagittal parietal cortex is a watershed zone supplied by distal branches of both the anterior and middle cerebral arteries. During systemic hypotension or circulatory arrest, perfusion pressure falls first at these distal field territories, producing characteristic border zone infarcts. Posterior cerebral territory emboli typically cause occipital lesions with visual deficits, sagittal sinus thrombosis gives hemorrhagic convexity infarcts, and lacunes affect small deep perforators, not this cortical distribution.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

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Written and medically reviewed by the StethoPrep medical team.