Spatial and quantitative distribution of human peritumoural brain oedema in computerized tomography.

Computerized tomography (CT) was used to study the pathways of oedema spreading in man. Based on the assumption that local changes in CT numbers in oedematous white matter closely correspond to changes in tissue water content, CT numbers of consecutive tissue blocks of 3.0-3.6 mm were examined in the main directions of oedema spreading: towards the deep white matter, towards the cortex and towards the ventricle. Tumours with oedema grade II and III showed a reduction of CT number of 10 +/- 1.8. The corresponding increase in water content of about 10-12% seems to be an upper limit of fluid accumulation in the white matter. From this oedema centre, water content very slowly and gradually decreased along the oedema projection into the deep white matter. In contrast, if oedema reached the cortex of adjacent gyri, the decline in water content was very sharp. A similar observation was made in the external capsule where oedema sharply declined at the border to the adjacent grey matter, putamen and claustrum. Oedema projection towards the ventricle showed a nearly uniform magnitude from the centre to the ventricular lining, suggesting a certain resistance by a limited capacity of transependymal drainage of oedema fluid. It is assumed that the spatial distribution and extension of oedema around a brain tumour is determined by a system of differential resistance to fluid movement in the following order: grey matter--ventricular lining--white matter.