Neuroassistant

MRI in acute ischemic stroke

Early hyperacute phase: 0-6 hours. Late hyperacute phase: 6-24 hours
Diffusion restriction becomes apparent as high signal on DWI and low ADC values on 95% of infarcts within minutes after onset
2-7% of patients with stroke may initially have a normal DWI. This may be attributable to small infarcts, early clot lysis/recanalization, brainstem lesions and moderate or fluctuating hypoperfusion
In the early hyperacute phase, T1 is usually normal. Hypointensity (edema) becomes apparent on T1 within 12-24 hours. Loss of expected flow-void may reflect vessel occlusion or reduced flow
Contrast-enhanced T1 may show intravascular enhancement (parenchymal enhancement is uncommon in hyperacute phase)
30-50% of strokes show cortical swelling and hyperintensity on T2/FLAIR within the first 4 hours
Almost 100% of strokes show swelling and hyperintensity on FLAIR at 7 hours and on T2 at 12-24 hours after onset
Intraarterial hyperintensity on FLAIR may be an indicator of slow blood flow
FLAIR/DWI mismatch (high signal on DWI with normal FLAIR) may be an indicator of viable ischemic penumbra
DWI reflects the non-salvable ischemic core, perfusion weighted imaging (PWI) reflects the salvable, at-risk ischemic penumbra
SWI or T2* imaging may reveal hemorrhagic areas as early as 8-12 hours or as late as 5 days

High DWI signal and low ADC values continue to the end of the first week
Hyperintensity on T2/FLAIR progressively increases during the first 4 days
Hypointensity on T1 but some cortex may show high T1 values at 3+ days after onset due to cortical laminar necrosis
Parenchymal enhancement may be apparent at 5+ days after onset
Less common enhancement patterns: meningeal (after 2-6 days), arterial (after 3 days)

ADC values start to increase and demonstrate pseudonormalisation at 10-15 days
DWI high signal may persist due to T2 “shine-through”
Hypointensity on T1 occasionally with areas of high T1 signal due to cortical laminar necrosis
Cortical enhancement on contrast-enhanced T1

Low T1 signal. Some cortex may show intrinsically high T1 signal due to cortical laminar necrosis
High T2/FLAIR signal
Cortical enhancement may persist 2-4 months
DWI may decrease or remain high due to T2 shine-through. ADC values are high