Formation and propagation of brain oedema fluid around human brain metastases. A CT Study.

Computerized tomography (CT) was used to examine the time-course of the propagation of extravasated contrast medium from small brain metastases into the peritumoural oedematous white matter, following infusion of 200 ml of meglumine amidtrizoate for 3 hours. Four patients with a metastatic brain tumour were examined. CT scans at identical levels were taken 1.5, 3, 6, 9, and 12 hours after start of contrast infusion. Following 4-7 days of dexamethasone treatment (8-12 mg/day i.v.) the examination was repeated. A contrast-enhanced area was observed surrounding the clearly delineated tumours, expanding gradually in a circular fashion into the peritumoural white matter oedema. The expanding circular enhancement was measured planimetrically on the various scans. From these values, the increase in radius/hr respectively in volume/hr was calculated, assuming a spherical geometry. This enabled a determination of the rate of oedema fluid formation and of the speed of oedema fluid propagation. The formation rate of oedema fluid amounted to 0.5-3.2 ml/hour and the speed of oedema fluid spreading to 1.9 mm/hour. Following treatment with dexamethasone the formation rate of oedema fluid is reduced by 30-50%. The important clinical implications of these new findings are discussed.