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Difficulty: MediumInterpreting Imaging Results

A 65-year-old woman with a history of atrial fibrillation is evaluated for sudden-onset right-sided hemiparesis and expressive aphasia. The neurology team discusses the expected neuroimaging evolution of a large middle cerebral artery territory infarction.

Arrange the following expected magnetic resonance imaging (MRI) head findings in chronological order of their appearance, from earliest (hyperacute phase) to latest (chronic phase).

  1. 1Restricted diffusion on Diffusion-Weighted Imaging (DWI)
  2. 2Parenchymal hyperintensity on T2-Fluid-Attenuated Inversion Recovery (FLAIR) sequences
  3. 3Parenchymal gadolinium enhancement on T1-weighted sequences
  4. 4Cystic encephalomalacia and ex vacuo ventricular dilation

Answer

The correct chronological appearance of ischemic stroke MRI findings is: DWI restricted diffusion (minutes), followed by T2-FLAIR hyperintensity (hours), then subacute parenchymal gadolinium enhancement (days to weeks), and finally chronic cystic encephalomalacia (months to years).
The temporal evolution of an ischemic stroke on MRI reflects the underlying pathophysiological cascade. The earliest finding is restricted diffusion on DWI (minutes) caused by cytotoxic edema. This is followed by T2-FLAIR hyperintensity (4-6 hours) as vasogenic edema sets in. During the subacute phase (1-2 weeks), blood-brain barrier breakdown allows for parenchymal contrast enhancement. Ultimately, the chronic phase (months to years) is characterized by tissue loss, leaving behind cystic encephalomalacia and adjacent ex vacuo ventricular dilation.

Step-by-Step Solution

1
Identify the hyperacute findings that appear within minutes to hours.
DWI restricted diffusion is the first finding to appear.
Immediate failure of the Na+/K+ pump leads to cytotoxic edema, which restricts the diffusion of water molecules.
2
Identify the acute findings that emerge over several hours.
T2-FLAIR hyperintensity appears next.
As vasogenic edema develops secondary to early endothelial injury, free water content in the tissue increases, causing hyperintensity on T2 and FLAIR sequences after approximately 4-6 hours.
3
Identify the subacute findings that appear over days to weeks.
Parenchymal gadolinium enhancement is identified in the subacute stage.
Frank disruption of the blood-brain barrier occurs several days after the initial insult, allowing intravenous contrast to leak into the brain parenchyma.
4
Identify the chronic findings that take months to years to develop.
Cystic encephalomalacia and ex vacuo dilation occur last.
Once the inflammatory and necrotic debris is completely cleared by macrophages, a permanent fluid-filled cavity remains, accompanied by focal brain volume loss.

Key Concept

Chronological evolution of ischemic stroke on MRI
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Topics

Interpreting Imaging Results

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