EARLY CHANGES IN PERITUMOROUS EDEMA AND CONTRALATERAL WHITE-MATTER AFTER DEXAMETHASONE - A STUDY USING PROTON MAGNETIC-RESONANCE SPECTROSCOPY

Aims-To study the mechanism of action of steroids in patients with per itumorous oedema. Methods-To investigate early cerebral metabolic chan ges proton magnetic resonance spectroscopy (H-1-MRS) was used before a nd 11 to 14 hours after treatment with dexamethasone (12 mg oral loadi ng and 4 mg four times daily maintenance). Nine patients (two men, sev en women, mean age 54) with pronounced oedema associated with various intracranial tumours (two astrocytomas, three meningiomas, two gliobla stoma, and two metastases) were examined using MRI and MRS. SE1500/135 volume selected MRS (mean volume 21 mi) were performed on an oedemato us region and a contralateral region. All spectra were acquired with a nd without water suppression. Metabolite peak area ratios were determi ned. Results-Regions of oedema had significantly (P < 0.01) higher uns uppressed water than the contralateral regions, as expected. There was no change at this early time point after dexamethasone. The ratio of the area of choline containing compounds to that creatine and phosphoc reatine compounds was determined after which the serial ratios of thes e before and after were calculated (a serial ratio of 1.0 would indica te no change in the choline to creatine ratios after steroid administr ation). The mean serial ratios for the area of oedema were 1.02 (SEM 0 .08) and 1.10 (0.08) for the contralateral volume of interest, indicat ing no significant changes. However, significant changes (P < 0.02) we re found in the N-acetyl-aspartate (NAA)/choline serial ratios (0.86 ( 0.06) in the area of oedema, 1.20 (0.10) in contralateral brain) and t he NAA/creatine serial ratios (0.86 (0.08) for the oedema, 1.25 (0.11) in contralateral brain). Conclusions-Such rapid changes may be explai ned either by relatively large alterations in the relaxation character istics of NAA or, more controversially, by actual changes in the amoun ts of NAA. It is proposed that steroids act primarily by causing early metabolic changes that are later expressed in improvements in intracr anial volume relations.