What does an old stroke appear like on Fluid Attenuated Inversion Recovery (FLAIR) Magnetic Resonance Imaging (MRI) in a typical older adult with a history of stroke and comorbidities such as hypertension, diabetes, and cardiovascular disease?

Appearance of Old Stroke on FLAIR MRI

Old strokes appear as hyperintense (bright) lesions on FLAIR MRI, representing areas of permanent tissue infarction with gliosis and increased water content in the damaged brain parenchyma. 1

Characteristic Imaging Features

Signal Characteristics

• Hyperintense signal on FLAIR sequences indicates completed infarction with cellular death, distinguishing old strokes from acute ischemic changes that appear on diffusion-weighted imaging (DWI) first 1
• The hyperintensity reflects permanent tissue damage with gliosis, demyelination, and increased interstitial water content in the infarcted territory 2
• FLAIR is superior to CT for detecting old infarcts, particularly small cortical, small deep, and posterior fossa lesions 1

Location Patterns

• Embolic strokes from carotid disease typically show multiple small cortical infarcts in the middle cerebral artery (MCA) territory and vascular border-zone areas 1
• Lacunar infarctions appear as small, deep hyperintense lesions, most commonly in the basal ganglia and periventricular white matter 1
• Watershed infarcts occur in border zones between major cerebral arterial territories, reflecting hemodynamic compromise 1

Temporal Evolution

Acute to Chronic Transition

• DWI lesions appear within minutes of ischemia onset, showing cytotoxic edema 1
• FLAIR hyperintensity develops once cellular death occurs, typically becoming visible hours after symptom onset 1
• In the International Carotid Stenting Study, most acute DWI lesions did not progress to permanent FLAIR lesions at 30 days, particularly when small and treated quickly 1

Chronic Appearance

• Old infarcts remain permanently hyperintense on FLAIR due to gliosis and tissue loss 1
• The lesion margins become well-defined over time as the acute inflammatory response resolves 1

Clinical Significance

Silent Brain Infarctions

• 28-31% of older adults without prior stroke history have MRI-detected infarcts ("silent" infarcts) 3
• These silent infarcts are associated with impaired cognition, neurological deficits, and doubled risk of future stroke 1, 3
• Despite being clinically "silent," these lesions correlate with measurable cognitive impairment and abnormal neurological examination findings 3

Risk Stratification

• Presence of old infarcts on FLAIR imaging indicates two-fold increased risk of future stroke events 1
• In patients with TIA, positive DWI/FLAIR findings predict increased 10-year risk of recurrent ischemic stroke (HR 2.66) 1

Important Diagnostic Considerations

Distinguishing Features

• Old infarcts show no restricted diffusion on DWI (unlike acute strokes), as the ADC values normalize after the acute phase 1
• FLAIR can distinguish acute from chronic ischemia better than CT 1
• Gradient echo sequences detect associated microhemorrhages, which may indicate underlying cerebral amyloid angiopathy or hypertensive vasculopathy 1

Common Pitfalls

• FLAIR overestimates demyelination in periventricular regions due to increased blood-brain barrier permeability and plasma leakage with aging 2
• Perivascular FLAIR hyperintensities may not always represent true infarction—in one study, 12 of 14 cases with prominent perivascular WMH showed no corresponding demyelination on pathology 2
• Do not confuse focal splenial hyperintensity (common with aging and radiation therapy) with acute pathology 4

Associated Findings

• White matter hyperintensities often coexist with old infarcts, particularly in patients with hypertension and diabetes 1, 5
• Multiple microbleeds on gradient echo sequences suggest underlying small vessel disease or cerebral amyloid angiopathy 1
• Superficial siderosis may indicate cerebral amyloid angiopathy when present with lobar infarcts 1