1. Department of Neurological Surgery, University of Virginia, Charlottesville, VA 22908, USA
2. Department of Radiology, University of Virginia, Charlottesville, VA 22908, USA
3. Department of Neurosurgery, Thomas Jefferson University, Philadelphia, PA 19107, USA
4. Department of Neurological Surgery, University of Iowa, Iowa City, IA 52242, USA
5. Department of Neurological Surgery, Tulane University, New Orleans, LA 70112, USA