Pure motor lacunar infarcts most often involve which arterial territory?

• A. Anterior choroidal artery
• B. Lenticulostriate arteries
• C. Middle cerebral artery cortical branches
• D. Posterior cerebral artery

Answer: (B)

Small vessel occlusion in deep brain structures disrupts the corticospinal tract as it travels through the posterior limb of the internal capsule, producing pure motor weakness without cortical signs. The lenticulostriate arteries are tiny penetrating branches of the middle cerebral artery that supply the posterior limb of the internal capsule and nearby basal ganglia. When one of these vessels becomes occluded—often due to lipohyalinosis from chronic hypertension—a lacunar infarct forms, yielding the characteristic pure motor deficit on the opposite side. Other choices involve cortical areas or different territories, which would produce additional symptoms (language, neglect, visual field defects, etc.), not the pure motor picture.