Guide to Dating An Ischemic Stroke

This is a handy table that summarizes the findings of different MRI sequences in the evolution of stroke.

  • SWI may differentiate hemorrhagic transformation from cortical necrosis.
  • DWI may be falsely negative in patients with hyperacute or acute posterior circulation / lacunar stroke.
  • In hyperacute stages, large area of enhancement in deep gray matter or basal ganglia may indicate impending hemorrhagic transformation.
  • Increased parenchymal cortical enhancement should end around 48h after stroke.
  • If parenchymal enhancement persists for >8weeks, other causes should be considered.
  • Arterial and meningeal enhancement should end around 1 week after stroke.
  • Cortical necrosis usually resolves by 3 months after stroke and rarely persists for more than a year

The illustration below will help  you visualize the timeline of MRI changes in stroke.

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EXAMPLE CASES (taken from the article referenced below):

 

#1

1.JPG

Chronic lacunar stroke in an 82-year-old man with diabetes, hypertension, and altered mental status.

  • (a) Diffusion-weighted MR image shows an area of low signal intensity in the left centrum semiovale (arrow).
  • (b) ADC map shows an area of high signal intensity in the left centrum semiovale (arrow).
  • (c) Unenhanced T1-weighted MR image shows an area of low signal intensity in the left centrum semiovale (arrow).
  • (d) Gadolinium-based contrast-enhanced T1-weighted MR image shows an area of contrast enhancement in the left centrum semiovale (arrow).
  • (e) T2-weighted MR image shows an area of high signal intensity in the left centrum semiovale (arrow). These findings are consistent with a chronic lacunar stroke with resultant cystic encephalomalacia

#2

2.JPG

Early hyperacute stroke in a 49-year-old woman with right lower extremity weakness and rigidity.

  • (a, b) ADC map (a) and diffusion-weighted MR image
  • (b) show an area of restricted diffusion in the left motor cortex (arrow).
  • (c) FLAIR image shows a corresponding area of slightly high signal intensity (arrow).
  • (d) Gadolinium-based contrast-enhanced T1-weighted MR image shows arterial enhancement (arrows). No parenchymal enhancement is seen.
  • (e) T2-weighted MR image shows an area of high signal intensity in the left motor cortex (black arrow), a finding indicative of a stroke that occurred more than 6 hours earlier (late hyperacute). Other scattered nonspecific subcortical areas of high signal intensity are also seen (white arrows), confounding the finding of late hyperacute stroke.
  • (f) No hemorrhagic transformation is seen at susceptibility-weighted MR imaging. Because of the presence of early arterial enhancement and only slightly high signal intensity at FLAIR imaging, the stroke is likely less than 6 hours old (early hyperacute). In fact, this patient presented to the emergency department within 3 hours of the onset of symptoms.

#3

3a.JPG

3b.JPG

Early subacute stroke in an 87-year-old woman who presented with left hemineglect with an unknown time of onset.

  • (a) ADC map shows an area of low signal intensity in the right parietooccipital junction (arrow), a finding that usually persists for about 1 week. This area demonstrates high signal intensity at diffusion-weighted imaging (not shown).
  • (b) FLAIR MR image shows a corresponding area of high signal intensity (arrow).
  • (c) T1-weighted MR image shows a corresponding area of low signal intensity (arrow).
  • (d) Gadolinium-based contrast-enhanced T1-weighted MR image shows parenchymal enhancement in the affected area (arrow). Parenchymal enhancement is usually seen about 1 week after stroke.
  • (e) T2-weighted MR image shows a corresponding area of high signal intensity (arrow).
  • (f, g) Susceptibility-weighted minimum intensity projection (f) and susceptibility-weighted phase(g) MR images show early blood products (arrow) indicative of hemorrhagic transformation. These findings are indicative of an early subacute stroke, likely around 7–10 days old. Further questioning of the nursing home staff revealed that the symptoms were present for about 1 week.

#4

4.JPG

Chronic stroke in a 67-year-old man with a history of head and neck cancer. MR imaging was performed to further evaluate an area of hypoattenuation in the right occipital lobe at recent fused positron emission tomography/computed tomography (PET/CT).

  • (a)Diffusion-weighted MR image shows an area of low signal intensity in the right occipital lobe (arrow) with a peripheral rim of high signal intensity, a finding that may be due to T2 shine-through.
  • (b) ADC map shows a corresponding area of high signal intensity (arrow).
  • (c) Susceptibility-weighted MR image shows hemorrhagic products (arrow) in the right occipital lobe.
  • (d) T2-weighted MR image shows an area of high signal intensity in the right occipital lobe (arrow).
  • (e) T1-weighted MR image shows a corresponding area of low signal intensity (arrow).
  • (f) Contrast-enhanced T1-weighted MR image shows a corresponding area of parenchymal enhancement (arrow). These findings are indicative of a chronic stroke that is likely 3 weeks to 2 months old. At further questioning, the patient reported experiencing recent left visual field defects, but he could not remember exactly when they started.

References

Allen, Laura M. et al. “Sequence-Specific MR Imaging Findings That Are Useful In Dating Ischemic Stroke”. RadioGraphics 32.5 (2012): 1285-1297. Web.

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