Fogging phenomenon (cerebral infarct)
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The 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, hypoattenuation and swelling become more marked, resulting in significant mass effect and clear demarcation of the infarct often with vivid gyral enhancement 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 a number of processes occurring simultaneously including the migration of lipid-laden macrophages and leukocytes into the infarcted tissue, proliferation of capillaries, extravasation of red blood cells out of damaged capillaries and a decrease in edema 1-3,7.
At 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 MRI sequences 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 the onset of infarction 5.
- 1. Becker H, Desch H, Hacker H et-al. CT fogging effect with ischemic cerebral infarcts. Neuroradiology. 1979;18 (4): 185-92. - Pubmed citation
- 2. Chalela JA, Kasner SE. The fogging effect. Neurology. 2000;55 (2): 315. Neurology (full text) - doi:10.1212/WNL.55.2.315 - Pubmed citation
- 3. Scuotto A, Cappabianca S, Melone MB et-al. MRI "fogging" in cerebellar ischaemia: case report. Neuroradiology. 1998;39 (11): 785-7. Pubmed citation
- 4. Skriver EB, Olsen TS. Transient disappearance of cerebral infarcts on CT scan, the so-called fogging effect. Neuroradiology. 1982;22 (2): 61-5. Pubmed citation
- 5. O'Brien P, Sellar RJ, Wardlaw JM. Fogging on T2-weighted MR after acute ischaemic stroke: how often might this occur and what are the implications?. Neuroradiology. 2004;46 (8): 635-41. Neuroradiology (full text) - doi:10.1007/s00234-004-1230-2 - Pubmed citation
- 6. “Cerebral Infarction Diagnosis by Computerized Tomography: Analysis and Evaluation of Findings”—How Far Have We Really Come?. AJR. 2006;186 (3): 611-612. AJR (full text) - doi:10.2214/AJR.05.0954
- 7. Ricarte IF, Pedroso JL, Carvalho FA, Abrahão A, Valiente RA, Alves MM, Gomes DL, Silva GS. The essential can be invisible to the eyes: the "fogging effect" phenomenon in the subacute stage of ischemic stroke. (2013) Journal of stroke and cerebrovascular diseases : the official journal of National Stroke Association. 22 (8): e628-9. doi:10.1016/j.jstrokecerebrovasdis.2012.08.009 - Pubmed