1. Department of Neurosurgery, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania
2. Department of Neurology, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania
3. Departments of Neurosurgery and Anesthesiology and Critical Care, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania
4. Departments of Neurosurgery, Neurology, and Anesthesiology and Critical Care, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania