Understanding the difference between theory and practice: The extracranial-intracranial bypass trials in prevention of ischemic stroke

Background: Patients with atherosclerotic carotid or middle cerebral artery occlusions suffer ischemic events that might theoretically be preventable with a surgical extracranial-intracranial bypass, but theory by itself does not justify surgical interventions. Methods: We review landmark randomized trials on EC-IC bypass surgery for the treatment of ischemic stroke in patients with atherosclerotic stenoses or occlusions. Results: The initial EC-IC bypass trial from 1985 did not show any clinical benefit from surgery. The carotid occlusion surgery study (COSS) performed more than 20 years later included only patients highly selected to potentially benefit from bypass by using modern perfusion studies. While EC-IC bypasses were successfully created and they did improve cerebral perfusion, the COSS study also failed to show any clinical benefit to the participating patients. Conclusion: Neurosurgical interventions must not only work in theory; they must improve patient outcomes in real practice.