A computed tomography study on formation, propagation, and resolution of edema fluid in metastatic brain tumors.

Propagation of contrast medium, which extravasated from small metastatic brain tumor, was imaged via CT. By maintaining a constant blood level of the contrast medium by prolonged infusion of 200 ml of 60% meglumine amidtrizoate for 3 hr and thus maintaining a constant passage of contrast labeled edema fluid into the peritumoral extracellular space, the spread of the newly formed edema fluid can be imaged by repeated CTs as a gradually expanding peritumoral circular enhancement into the neighboring white matter. Four patients with small metastatic brain tumor were investigated. CT scans were taken at identical levels 1.5, 3, 6, 9, and 12 hr after start of contrast infusion. After 4 to 7 days of dexamethasone treatment (0.15-0.25 mg/kg/day), the examination was repeated. The area of the expanding circular enhancement was planimetrically measured. From these values, the increase in radius per hour, respectively, in volume per hour were calculated assuming a spherical geometry. These data enabled a determination of the formation rate of edema fluid, of the speed of edema propagation, and of the resolution rate of edema fluid during tissue passage. The formation rate of edema fluid amounted to 0.6 to 3.2 ml/hr depending on tumor diameter and was reduced by about 30% after dexamethasone treatment. Edema fluid traveled 4.8 mm during the first 180 min and 1.9 mm during the consecutive 90 min. The resolution rate of edema fluid during tissue passage amounted to 0.05 ml/hr/cm3 white matter before dexamethasone treatment.