ROLE OF VASOGENIC EDEMA AND TISSUE CAVITATION IN ISCHEMIC EVOLUTION ON DIFFUSION-WEIGHTED IMAGING - COMPARISON WITH MULTIPARAMETER MR AND IMMUNOHISTOCHEMISTRY

PURPOSE: To examine the mechanisms of further evolution that occurs fr om the early to late phase after initial changes in diffusion-weighted imaging after cerebral ischemia. METHODS: Sprague-Dawley rats were su bjected to middle cerebral artery occlusion. Diffusion-, proton densit y-, T1- and T2-weighted imaging were performed on days 0, 2, and 6. Hi stologic examination (IgG, glial fibrillary acidic protein, and cresyl violet staining) was done after scanning. RESULTS: Apparent diffusion coefficients (ADCs) in the ischemic hemisphere were significantly dec reased on day 0. Thereafter, ADCs increased over time and became signi ficantly higher than the contralateral side by day 6. Changes in basal ganglia occurred more rapidly than in cortex. Proton density-, T1-, a nd T2-weighted scans showed maximal changes on day 2. From day 0 to da y 2, there are significant correlations between changes in ADC and cha nges in T1-weighted signals and T2-weighted signals. Histologic exam s howed early neuronal injury on day 0, intense gliotic activity and pro tein leakage associated with infarction and edema on day 2, and cavita tion in severely infarcted areas on day 6. CONCLUSION: After initial r eduction of ADC, the subsequent increase in ADC values on day 2 may be associated with vasogenic edema and cell lysis. Later elevations in A DC may be related to cavitation of infarcted tissue.