Fogging effect phenomenon

Case contributed by Adan Radiology Department


The patient was admitted with decreased level of consciousness and left-sided body weakness (acute CVA). Known history of diabetes mellitus, hypertension, and headache. CT brain was performed to rule out hemorrhagic transformation.

Patient Data

Age: 90 years
Gender: Female

Initial CT brain.

  • in the proper MCA territory, a well-defined wedge-shaped hypodense cortical and subcortical area is seen at the right frontal lobe effacing cortical sulci of acute stage ischemic stroke
  • exaggerated deep periventricular white matter hypodensity of small vessels disease
  • no evidence of hemorrhage, masses or midline shift
  • age-related prominent ventricular system and peripheral CSF spaces 
  • the bony calvarium showed hyperostosis frontalis internal (normal variant) with no destructive lesion

After 9 days CT brain


Comparison is made with the above CT study done 9 days before showed:

  • an interval improvement of the previously noted right frontal lobe wedge-shaped hypodensity of acute infarction which become currently less hypodense to isodense (decreased brain edema and evidence of reversal of previously noted hypodensity) suggesting phenomena of fogging effect for clinical correlation
  • no evidence of new lesions. No intra- or extra-axial hemorrhage is detected
  • small sub-centimeter focal hypodense areas are noted at the right centrum semiovale suggestive of old lacunar infarction
  • the rest of the findings are unaltered

Case Discussion

A 90-year-old female patient with a medical history of diabetes mellitus and dyslipidemia presented to the emergency department with an acute onset of left-sided hemiplegia. A non-contrast CT scan of the head was performed, which depicted proper right middle cerebral artery (MCA) territory acute stage of ischemic stroke with no evidence of intracranial hemorrhage (ICH). 

A subsequent CT brain after 9 days demonstrated interval improvement of right frontal lobe wedge-shaped hypodensity of acute infarction, which became currently less hypodense to the isodense suggesting fogging effect phenomena.

The non-enhanced CT scan may lead to an underestimation of an infarct’s extension in the subacute stage of cerebral infarction, which requires clinical correlation and complementary examinations (contrast-enhanced CT or MRI scans) to infer true size.

Case courtesy Dr Safwat Al Moghazi MD.

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