A STUDY ON PERITUMOURAL BRAIN EDEMA AROUND MENINGIOMAS BY CT AND MRI SCANNING

There is a great variability in the amount of peritumoural brain oedem a accompanying meningiomas. In a previous study it was found that the degree of brain oedema in the white matter around meningiomas correlat ed with disruption of the layers (especially the cerebral cortex), whi ch separate the tumour from the white matter, as well as with the size and histological subtype of the tumour.In the present study comprisin g 9 meningiomas, the volume of oedema was calculated by integration of the cross-sectional oedematous areas on serial MRI slices. The volume of oedema was zero in 3 cases and ranged from 11 to 176.4 ml in the o ther 6 cases. The MRI-scans also showed disruption of the cortex in al l cases, ranging from slight to severe. T1 and T2 measurements were ma de at the level of maximum extension, using a mixed sequence at a fiel d strength of 1.5 T. From the T2 values tissue water content in % was calculated using the equations: WC = 39.36/(R2 + 37.2) for cortex, and WC = 29.63/(R2 + 27.8) for white matter. These had been obtained by c orrelating water content with relaxation rates, measured in vitro on h uman brain autopsy specimens which were subjected to hydration with di stilled water or dehydration by hyperosmolar solutions. Mean water con tent amounted to 82.53% for normal cortex, 74.72% for normal white mat ter, and 84.59% for oedematous white matter around the tumour. On the assumption that the spread of contrast agent marks the advancement of the front of oedema produced by the tumour, CT-studies were made befor e, and at 1 1/2, 3 and 6h after contrast infusion. The increase in dia meter of the contrast-stained area on the CT-scan allows calculation o f the excess of oedema production per unit tumour volume. Of 6 tumours with oedema (mean peritumoural water content of 91% and mean volume o f oedema of 69.2 ml) the production excess at the steady-state was 0. 18-1.08 ml/h/cm3 tumour volume, whereas 3 tumours without associated o edema had a production ''cess of 0.03-0.12ml/h/cm3. Moreover, penetrat ion of the cortex seems to constitute a separate factor determinig the spread of oedema.