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Difficulty: MediumInterpreting Imaging Results

A 65-year-old man with a history of atrial fibrillation presents to the emergency department with acute onset right-sided hemiparesis and expressive aphasia. If magnetic resonance imaging (MRI) of the brain is obtained over the course of his illness, arrange the following characteristic imaging findings of an ischemic stroke in the correct chronological order of their typical initial appearance, from earliest to latest.

  1. 1Restricted diffusion on Diffusion-Weighted Imaging (DWI)
  2. 2Hyperintensity on Fluid-Attenuated Inversion Recovery (FLAIR) imaging
  3. 3Cortical gyral enhancement on T1-weighted post-contrast imaging
  4. 4Cystic encephalomalacia and focal volume loss

Answer

The correct chronological order of appearance is: Restricted diffusion on DWI (minutes), followed by Hyperintensity on FLAIR (4-6 hours), then Cortical gyral enhancement (1-2 weeks), and finally Cystic encephalomalacia (months to years).
The correct sequence mirrors the pathophysiological evolution of a cerebral infarction. Cytotoxic edema occurs almost immediately after blood flow ceases, restricting water molecule movement and causing hyperintensity on DWI within minutes. As cell membranes fail and fluid leaks into the interstitial space over the next several hours (typically 4-6 hours), vasogenic edema develops, which is seen as hyperintensity on T2 and FLAIR sequences. By the end of the first week (subacute phase), breakdown of the blood-brain barrier occurs, leading to characteristic cortical gyral enhancement on post-contrast imaging. Finally, in the chronic phase (months to years), macrophages clear the necrotic debris, leaving behind cystic cavities (encephalomalacia) and resulting in compensatory local volume loss.

Step-by-Step Solution

1
Identify the underlying pathology being described in the clinical vignette.
The acute onset of focal neurologic deficits in a patient with atrial fibrillation describes an acute ischemic stroke, likely cardioembolic in origin.
Recognizing the pathology is necessary to understand the expected sequence of pathophysiologic cellular changes in the brain parenchyma.
2
Determine the imaging modality and sequence most sensitive to hyperacute cellular changes.
Restricted diffusion on DWI is placed first.
Cytotoxic edema causes immediate restriction of water molecule movement, making DWI positive within minutes of ischemia.
3
Identify the onset of macroscopic tissue edema.
Hyperintensity on FLAIR is placed second.
Vasogenic edema takes longer to develop, typically making the infarcted tissue hyperintense on FLAIR and T2-weighted sequences after 4 to 6 hours.
4
Determine the timing of blood-brain barrier disruption and chronic tissue resorption.
Cortical enhancement is placed third, and encephalomalacia is placed fourth.
Blood-brain barrier breakdown allows contrast extravasation in the subacute phase (1-2 weeks). Eventual clearing of necrotic tissue leads to chronic cystic cavities and volume loss (months to years).

Key Concept

The temporal evolution of ischemic stroke on MRI proceeds sequentially from early cytotoxic edema (DWI), to vasogenic edema (FLAIR), to subacute blood-brain barrier breakdown (contrast enhancement), and finally to chronic tissue cavitation (encephalomalacia).
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Interpreting Imaging Results

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