1. From the Department of Radiology, The Permanente Medical Group, Kaiser Permanente Medical Center, Santa Clara, 700 Lawrence Expy, Santa Clara, CA 95051 (M.D.M., P.Y.S.); Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, Calif (M.D.M., W.P.D.); and Department of Neurosurgery, The Permanente Medical Group, Kaiser Permanente Medical Center, Redwood City, Redwood City, Calif (M.F.S.).