A 72-year-old woman with a history of atrial fibrillation not on anticoagulation presents with acute right hemiparesis and expressive aphasia. Which finding most reliably distinguishes a lacunar infarct from a territorial (cortical) infarct in acute ischemic stroke?

## Lacunar vs. Territorial (Cortical) Ischemic Stroke ### Defining Characteristics **Key Point:** Cortical signs (aphasia, neglect, visual field defects, gaze deviation) are the hallmark of territorial/cortical infarcts and reliably distinguish them from lacunar infarcts, which spare cortical function. ### Comparison Table | Feature | Lacunar Infarct | Territorial (Cortical) Infarct | | --- | --- | --- | | **Size** | < 15 mm diameter | Large, involving cortical territory | | **Location** | Deep white matter, basal ganglia, brainstem, pons | Cortical and subcortical (MCA, ACA, PCA territory) | | **Cortical signs** | Absent (pure motor, sensory, or ataxic) | Present (aphasia, neglect, visual field defect, gaze deviation) | | **Etiology** | Small vessel disease (lipohyalinosis) | Large vessel atherosclerosis or cardioembolism | | **Classic syndromes** | Pure motor stroke, pure sensory stroke, ataxic hemiparesis | Broca's aphasia, Wernicke's aphasia, hemispatial neglect | | **Prognosis** | Better functional recovery | More severe disability, higher mortality | ### Pathophysiological Basis **High-Yield:** Lacunar infarcts result from occlusion of small penetrating arteries (branches of MCA, ACA, PCA, basilar artery) due to lipohyalinosis from chronic hypertension. They affect subcortical structures (internal capsule, basal ganglia, pons) while sparing the cortex. Territorial infarcts result from occlusion of large vessels (MCA, ACA, PCA) and involve both cortical and subcortical territories. Because the cortex is involved, higher cortical functions (language, spatial awareness, visual processing) are disrupted. ### Clinical Pearl **Clinical Pearl:** A patient presenting with pure motor weakness without any cortical signs (no aphasia, no neglect) and a small deep infarct on MRI is almost certainly a lacunar stroke. Conversely, the presence of any cortical sign indicates territorial involvement and rules out a pure lacunar syndrome. ### Mnemonic **Mnemonic:** **LACS** = Lacunar Anterior Circulation Stroke (pure motor, pure sensory, ataxic hemiparesis, dysarthria-clumsy hand). No cortical signs = lacunar. ### Why Cortical Signs Discriminate Cortical signs require intact cortical tissue to be damaged. Lacunar infarcts, by definition, spare the cortex and thus cannot produce aphasia, neglect, or visual field defects. The presence of even one cortical sign excludes a lacunar infarct.