Reversal of acute apparent diffusion coefficient abnormalities and delayedneuronal death following transient focal cerebral ischemia in rats

Twenty-two rats were subjected to 8, 15, 30, or 60 minutes of temporary mid dle cerebral artery occlusion (n = 5 per group) or sham occlusion (n = 2) i n the magnetic resonance imaging unit, Diffusion-, perfusion-, and T2-weigh ted imaging were acquired before and during occlusion, and after reperfusio n, A coregistration method was used to correlate the acute changes of the a verage apparent diffusion coefficient (ADC,) with the histology after 72 ho urs at the same topographic sites. The initially reduced ADC(av) values rec overed completely in both the lateral caudoputamen and upper frontoparietal cortex in the 8-, 15-, and 30-minute groups, partially in the cortex, and not at all in the caudoputamen in the 60-minute group. The histology showed that the caudoputamen was either normal or had mild neuronal injury in the 8-minute group and invariably had some degree of neuronal death in the 15- , 30-, and 60-minute groups, whereas the cortex was either normal or had va rying degrees of neuronal injury in all groups. No histological abnormaliti es were seen in the sham-operated rats. Our data suggest that acute ADC, re versal does not always predict tissue recovery from ischemic injury and tha t temporary focal ischemia for even 8-minute duration can cause delayed neu ronal death that is more severe in the caudoputamen where the initial ADC, decline was greater than in the cortex.