The CT appearance of cerebral infarction is highly time dependent. By 2 or 3 days after a stroke , low density is usually identifiable in the distribution of the occluded blood vessel. With large areas of infarction, edema and mass effect from the stroke can be seen. At 1 - 4 weeks after cerebral infarction enhancement from IV contrast material of the affected area can be identified. Old infarction is a sharply marginated area of low density with loss of brain substance.
Contrast enhancement lessens over time.
Acute subdural form crescentic shaped collections of high density material close to the calvarium. Can cause mass effect on underlying brain. As the hematoma ages, the collection becomes lower in density. Can enlarge rapidly and thus considered surgical emergencies. The dura is tightly adherent to the skull, so blood collecting between the calvarium and dura is usually under pressure.