What is a hemispheric infarct?

Definition of Hemispheric Infarct

A hemispheric infarct is an ischemic stroke involving a large territory of one cerebral hemisphere, most commonly affecting the entire or substantial portion of the middle cerebral artery (MCA) territory, with or without extension into adjacent anterior or posterior cerebral artery territories. 1

Clinical and Radiological Characteristics

Terminology and Scope

• The term "malignant middle cerebral artery infarction" was introduced in 1996 to describe infarction of the entire MCA territory appearing on CT within 48 hours, with or without infarction in other vascular territories 1
• Related terms include "large hemispheric infarction" and "massive hemispheric infarction," all describing the same clinical entity 2, 3
• Radiologically, extensive hemispheric infarction is defined as involving greater than 75% of the MCA territory, with or without involvement of adjacent anterior or posterior cerebral artery territories 4

Key Pathophysiological Features

• The hallmark is development of space-occupying cerebral edema between day 1 and day 3 after symptom onset 2
• Clinical deterioration results more from displacement of midline structures (thalamus and brainstem) than from globally increased intracranial pressure 1
• The mass effect causes displacement, distortion, and herniation of brain structures even when intracranial hypertension is initially absent 2
• ICP values may remain <20 mm Hg even in patients with deterioration from cerebral edema, suggesting displacement from mass effect is the primary mechanism 1

Clinical Presentation

Early Recognition

• Early neurological deterioration and severe hemispheric syndrome are characteristic 2
• The clinical course can follow different patterns: early worsening (within 24 hours), delayed worsening (over several days), or initially worsening followed by plateau and resolution (about a week) 1
• No reliable methods currently exist to predict the course of brain swelling 1

Epidemiology

• Extensive hemispheric infarction occurs in approximately 3.7% of all ischemic stroke cases 4
• Cardioembolic mechanism is likely in 58% of cases, with 42% having atrial fibrillation 4
• The infarction involves the MCA territory alone in 79% of cases, and adjacent anterior or posterior cerebral artery territories in 21% 4

Clinical Significance

Prognosis Without Intervention

• Mortality rates with conventional medical treatment alone can exceed 80% 2
• In-hospital mortality without surgical intervention reaches 52-76% 4, 5
• Of those who survive without surgery, 84% require nursing home care due to severe disability 4

Distinction from Other Stroke Types

• The initial experience with outcome assessment does not identify a major difference in outcome between dominant or nondominant hemispheric stroke 1
• Hemispheric infarcts differ from cerebellar infarcts in that cerebellar strokes often have good outcomes if there is no brainstem infarction 1

Important Clinical Pitfalls

Monitoring Considerations

• ICP monitoring or ventriculostomy placement has no value in patients presenting early with large supratentorial swollen hemispheric stroke 1
• This contrasts with cerebellar stroke with early swelling, where acute hydrocephalus may occur and ventriculostomy placement is often necessary 1

Associated Complications

• Cardiac arrhythmias or worsening of preexisting arrhythmias is common, particularly with infarcts involving the insular region 1
• Most cardiac arrhythmias are self-limited and do not require intervention 1
• Hyperglycemia is associated with increased edema and increased risk of hemorrhagic transformation 1