Histopathologic correlates of temporal diffusion changes in a rat model ofcerebral hypoxia/ischemia

BACKGROUND AND PURPOSE: Although diffusion-weighted MR imaging is a powerfu l tool for evaluating brain ischemia, histopathologic correlates of tempora l diffusion changes in cerebral hypoxia/ischemia have not been extensively examined. Diffusion-weighted MR imaging was used to evaluate the relationsh ip between the time course of apparent diffusion coefficient (ADC) changes and the histopathologic findings in cerebral hypoxia/ischemia, METHODS: Thirty 3-week-old rats were subjected to either a 15-, 30-, or 60- minute hypoxic/ischemic insult (unilateral common carotid artery ligation a nd exposure to 8% oxygen), during and after which diffusion- and T2-weighte d MR imaging was performed. Each animal was killed 48 hours or 6 hours afte r the insult, and fixed sections of the parietal cortex were examined by li ght microscopy, Ten other (control) rats were subjected to only unilateral common carotid artery ligation or hypoxia, RESULTS: The experimental rats showed three patterns of ADC change, dependi ng on the duration of the hypoxic/ischemic insult: transient (W-minute), bi phasic (15-, 30-, or 60-minute), and persistent (60-minute) ADC reduction p atterns. The transient ADC reduction pattern (reduction during the insult a nd recovery after resuscitation) was associated with selective neuronal dea th. The biphasic and persistent ADC reduction patterns (transient recovery and no recovery after resuscitation, respectively) were associated with cer ebral infarction. CONCLUSION: Different temporal patterns of ADC change are associated with d ifferent histopathologic findings. Although the clinical manifestations of these different histopathologic presentations are not yet defined, this stu dy indicates that sequential diffusion studies are a potentially powerful t ool in the evaluation of hypoxic/ischemic brain injury.