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

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Abstract
Computerized tomography (CT) was used to examine the timecourse 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 (8–12mg/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 0.5–3.2ml/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.