Ischemic lesions on Magnetic Resonance Imaging and histological outcomes after different transient periods of focal ischemia in rabbits

Objective The purposes of this study were to investigate the time course of ischemic changes on Magnetic Resonance Imaging(including DWI, PWI and T2WI) after different brief periods of focal brain ischemia in rabbits and to evaluate the histopathological outcomes in the regions of DWI abnormalities. Methods Sixty rabbits were subjected to 7 minutes (n=15); 15 minutes (n=15); 30 minutes (n=15) of middle cerebral artery occlusion ; and sham operation (n=15). Magnetic Resonance Imaging (including DWI, PWI and T2WI) were performed during before occlusion; 5min after occlusion and at 0.5, 2.0, 6.0, 12, 24, 48, and 72 hours after reperfusion. After the last MRI study at 72 hours after reperfusion, the brains were evaluated by histopathology. Results No MRI or histological abnormalities were observed in the sham-operated rabbits. In the 7-minute, 15-minute and 30-minute groups, the perfusion deficits and DWI hyperintensities that occurred during occlusion disappeared shortly after reperfusion. The DWI, PWI, and T2WI results remained normal thereafter in the 7-minute group, whereas secondary DWI hyperintensity and T2-WI abnormalities developed at the 6~12 hour observation point in the 15-minute and 30-minute groups. Histological examinations demonstrated neuronal necrosis in three groups, but the number of necrotic neurons was significantly higher in the 15-minute and 30-minute group than in the 7-minute group (P0.001). Conclusion Transient or permanent resolution of initial DWI lesions after reperfusion depends on the duration of ischemia. Transient resolution of DWI lesions is associated with widespread neuronal necrosis; moreover, permanent resolution of DWI lesions does not necessarily indicate complete salvage of brain tissue from ischemic injury. These results may help to explain the of neurological deficits in some patients who have normal DWI results after cerebral ischemia and cognitive deficits in some patients who experience transient ischemic attacks.