Effects of dexamethasone on cerebral perfusion and water diffusion in patients with high-grade glioma

Abstract

Background and purpose: The mechanisms by which the glucocorticoid dexamethasone produces its therapeutic action in patients with intracranial tumors still remain unclear. The purpose of this study was to investigate whether dexamethasone affects cerebral perfusion and water molecule diffusion by using quantitative dynamic susceptibility contrast perfusion MR imaging (DSC-MR imaging) and diffusion tensor MR imaging (DT-MR imaging).

Methods: Ten consecutive patients with glioblastoma multiforme underwent DSC-MR imaging and DT-MR imaging before and 48-72 hours after dexamethasone treatment (16 mg/day). Cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), and water mean diffusivity (<D>) were measured for enhancing tumor, nonenhancing peritumoral edematous brain, and normal-appearing contralateral white matter before and after steroid therapy. The percentage change in CBF, CBV, MTT, and <D> for the 3 tissue types was calculated for each patient, a mean value obtained for the population, and the statistical significance determined by using a paired-samples Student t test.

Results: After dexamethasone treatment, there was no significant change in tumor CBF, CBV, or MTT. Edematous brain CBV and MTT were also unchanged. There was, however, an increase in edematous brain CBF (11.6%; P = .05). <D> was reduced in both enhancing tumor (-5.8%; P = .001) and edematous brain (-6.0%; P < .001). There was no significant change in CBF, CBV, MTT, or <D> for normal-appearing contralateral white matter after treatment.

Conclusion: These data suggest that dexamethasone does not significantly affect tumor blood flow but may, by reducing peritumoral water content and local tissue pressure, subtly increase perfusion in the edematous brain.

Fig 1.

Images obtained from patient 4. A, Presteroid treatment contrast-enhanced T1-weighted volume image with region of interest indicating enhancing tumor. Pre- (B) and 72 hours (C) poststeroid treatment T2-weighted EP images with shaded and unshaded region of interest indicating enhancing tumor and nonenhancing peritumoral edematous brain.

Fig 2.

Images obtained from patient 4. [] (A and E), CBF (B and F), CBV (C and G), and MTT (D and H) maps obtained pre- (first row) and 72 hours poststeroid treatment. Note the reduction in [<D>] (red arrow) and the subtle increase in CBF for cortical/subcortical tissue within the edematous brain region (pink arrow). The maps are scaled to a maximum of 2500 × 10⁻⁶ mm²/s for [<D>], 75 mL/100 g/min for CBF, 7 mL/100 g for CBV, and 5 seconds for MTT.