What commonly used drug (in patients with brain masses) can result in dramatic reduction in oedema?
Dexamethasone is commonly used to reduce brain swelling, and in the setting of lymphoma (not thought to be the case here) can dramatically reduce the size of the mass in a matter of days. Keeping the possibility of dexamethasone effect when interpreting scans is important. In this case no dexamethasone (or antibiotics for that matter) were administered.
What is fogging?
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. It is believed to occur as the result of migration into the infarcted tissue (especially cortex) of of lipid-laden macrophages as well as proliferation of capillaries, and decrease in the amount of oedema.
When does it occur? How often?
After 2 to 3 weeks following an infarct the cortex regains near-normal density. Fogging is seen in around 50% of cases if imaged serially.
If you don't believe the diagnosis, or need to confirm your suspicion what imaging can be performed?
Contrast enhanced CT or MRI will demonstrate typical gyriform enhancement.
Single slice at the same level, obtained 7 days later, demonstrates essentially normal appearing brain.