1. Departments of Neurosurgery, Mayo Clinic, Rochester, Minnesota, United States
2. Department of Neurosurgery, University of Virginia Health System, Charlottesville, Virginia, United States
3. Department of Neurosurgery, University of Sherbrooke, Centre de Recherche Clinique Étienne-LeBel, Sherbrooke, Quebec, Canada
4. Department of Neurosurgery, University of Pittsburgh, Pittsburgh, Pennsylvania, United States