Fogging phenomenon - cerebellar stroke

Case contributed by Adam Hirschfeld


An 80-year-old patient, brought to the emergency department, due to a headache, dizziness and weakening of the left side muscles - 2 days post-onset of symptoms.

Patient Data

Age: 80 years
Gender: Female

Initial scan on the day of admission


Non-contrast CT of the brain, performed at first day, demonstrates an extensive low-density area of the completed ischemic stroke within the left cerebellar hemisphere. Minor hypodense stroke areas visible also in the right cerebellar hemisphere. There is a mass effect in the form of compression of the IV ventricle.

Control CT scan 10 days later


In the left cerebellar hemisphere hypodense area of the completed ischemic stroke is currently in large part isodense. The fourth ventricle is not compressed and the subarachnoid spaces above the left cerebellar hemisphere are narrow, preserved.

Case Discussion

The evolution in density of the lesion demonstrates the fogging phenomenon 1. Without being familiar with this transient phase of the evolution of cerebral infarct such findings can be misinterpreted and be a source of diagnostic confusion. Of course, taking into account the uncertain clinical case the possibility of lymphoma or mistake in patient data should be considered.

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