A

B

C

Cerebral infarction is hypodense (black) on CT scan. With progression of time (from A to C) the infarction gets more hypodense, more well defined and the mass effect gradually decreases with time due to gradual reduction of brain edema because the blood brain barrier is once again sealed. The initial hypodensity in acute infarction is due to edema (A) while the the ultimate hypodensity in old infarction (C) is due to astrogliosis with widened fluid filled extracellular spaces (microcavitations and macrocavitations). During the evolution of the infarction the edema and the swelling decreases and the infarction boundary becomes better defined, and the infarcted area becomes more hypodense.

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