1. Department of Neurosurgery, Vanderbilt University Medical Center, Nashville, Tennessee;
2. Data Coordinating Center, University of Utah, Salt Lake City, Utah;
3. Division of Neurosurgery, University of Calgary, Alberta, Canada;
4. Department of Neurosurgery, University of Toronto, Ontario, Canada;
5. Department of Neurosurgery, Washington University St. Louis, Missouri;
6. Department of Neurosurgery, Baylor College of Medicine, Houston, Texas;
7. Department of Neurosurgery, University of Washington Medical Center, Seattle, Washington;
8. Department of Neurosurgery, University of Alabama–Birmingham, Alabama;
9. Department of Pediatrics, University of Washington Medical Center, Seattle, Washington;
10. Department of Neurosurgery, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania; and
11. Department of Neurosurgery, University of Utah, Salt Lake City, Utah