[1] Harvard Univ, Sch Med, Brigham & Womens Hosp, Dept Neurosurg, Cambridge, MA 02138 USA
[2] Univ Calif San Francisco, Dept Neurol Surg, San Francisco, CA 94143 USA
[3] Emory Univ, Atlanta, GA 30322 USA
[4] Univ Pittsburgh, Dept Neurol Surg, Pittsburgh, PA 15260 USA