The histological effects of an intracranial arterial occlusion in the adult rat can be predicted on day 1 by the neurological score described in this report. Significant improvement can be obtained in these animals by reestablishing arterial flow 60 minutes or sooner after the ictus. The pattern of cortical pannecrosis observed after permanent occlusion (> or = 72 hours) was transformed into incomplete ischemic injury in most instances of transient occlusion.

Background and Purpose-The early ischemic lesions demonstrated by diffusion-weighted imaging (DWI) are potentially reversible. The purposes of this study were to determine whether resolution of initial DWI lesions is transient or permanent after different brief periods of focal brain ischemia and to evaluate histological outcomes. Methods-Sixteen rats were subjected to 10 minutes (nϭ7) or 30 minutes (nϭ7) of temporary middle cerebral artery occlusion or sham operation (nϭ2). DWI, perfusion-weighted imaging (PWI), and T 2 -weighted imaging (T 2 WI) were performed during occlusion; immediately after reperfusion; and at 0.5, 1.0, 1.5, 12, 24, 48, and 72 hours after reperfusion. After the last MRI study, the brains were fixed, sectioned, stained with hematoxylin and eosin, and evaluated for neuronal necrosis. Results-No MRI or histological abnormalities were observed in the sham-operated rats. In both the 10-minute and 30-minute groups, the perfusion deficits and DWI hyperintensities that occurred during occlusion disappeared shortly after reperfusion. The DWI, PWI, and T 2 WI results remained normal thereafter in the 10-minute group, whereas secondary DWI hyperintensity and T 2 WI abnormalities developed at the 12-hour observation point in the 30-minute group. Histological examinations demonstrated neuronal necrosis in both groups, but the number of necrotic neurons was significantly higher in the 30-minute group (95Ϯ4%) than in the 10-minute group (17Ϯ10%, PϽ0.0001). Conclusions-Transient

Arterial occlusions of short duration (< 25 minutes) produced, in 76 of 121 experiments (63%), brain lesions characterized by selective neuronal necrosis and various glial responses (or incomplete infarction). This lesion is entirely different from the pannecrosis/cavitation typical of an infarction that appears 3 to 4 days after a prolonged arterial occlusion. Delayed neuronal necrosis, secondary to a transient arterial occlusion or increasing numbers of necrotic neurons in experiments with variable periods of reperfusion, was a response observed only at a predictable segment of the frontoparietal cortex.