Variability and reversibility of focal cerebral ischemia in unanesthetized monkeys.

To assess reversibility of focal cerebral ischemia, we performed a neurologic and pathologic study of 27 monkeys subjected to temporary middle cerebral artery occlusion. An implanted snare ligature occluded the artery in awake monkeys for 30 minutes, 4 hours, 8 hours, 16 hours, 24 hours, or permanently. Serial neurologic observations were made for 2 weeks, and systematic neuropathologic examination estimated extent of infarction. Deficits from ischemia were commonly reversible at 30 minutes and 4 hours, but were rarely reversible after 8 hours. Neurologic deficit and infarct size showed remarkable variability. Maximum irreversible infarction evolved in about 4 to 8 hours in most awake monkeys. Variability and reversibility of focal ischemia were probably related to variable collateral circulation. The results suggested that emergency surgical revascularization might help some cases of acute ischemic stroke.