Fogging phenomenon

Fogging phenomenon is seen on non contrast CT of the brain and represents a transient phase of the evolution of cerebral infarct where the region of cortical infarction regains a near normal appearance. 

During the first week following a cortical infarct hypo-attenuation and swelling become more marked resulting in significant mass effect and clear demarkation of the infarct with vivid gyral enhancement usually seen at this time 6

As time goes on the swelling starts to subside and the cortex begins to increase in attenuation. This is believed to occur as the result of migration into the infarcted tissue of lipid-laden macrophages as well as proliferation of capillaries, and decrease in the amount of oedema 1-3. After 2 to 3 weeks following an infarct the cortex regains near-normal density and imaging at this time can lead to confusion or missed diagnosis 4-5. Fogging has been demonstrated in around 50% of cases 4

If in doubt the administration of IV contrast will demarcate the region of infarction 2

A similar phenomenon is also seen on T2 weighted sequences on MRI of the brain, and is believed to be due to similar cellular processes, as the timing is similar 3. It has been found to occur in approximately 50% of patients between 6 and 36 days (median 10 days) after onset of infarction 5

Stroke and intracranial haemorrhage
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Article information

rID: 21647
Section: Signs
Synonyms or Alternate Spellings:
  • CT fogging phenomenon
  • MRI T2 fogging phenomenon
  • Fogging phenomena

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Cases and figures

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    Case 1: 2 days post onset of symptoms
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    Case 1: 9 days post onset of symptoms
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