1. School of Medicine, Stanford University Medical Center , Stanford, CA 94305 , USA
2. Department of Neurosurgery, Larner College of Medicine at The University of Vermont , Burlington, VT 05405 , USA
3. Department of Neurosurgery, Dell Medical School, The University of Texas at Austin , Austin, TX 78712 , USA
4. Department of Medicine, Stanford University Medical Center , Stanford, CA 94305 , USA
5. Veterans Affairs Palo Alto Health Care System , Palo Alto, CA 94304 , USA
6. Department of Neurosurgery, Stanford University Medical Center , Stanford, CA 94305 , USA