[1] Univ Calif San Francisco, Dept Neurol Surg, San Francisco, CA 94143 USA
[2] Johns Hopkins Univ, Dept Neurol Surg, Baltimore, MD 21287 USA
[3] Univ Calif San Francisco, Dept Radiol, San Francisco, CA 94143 USA
[4] Univ Calif San Francisco, Dept Pathol, San Francisco, CA 94143 USA