1. 1Department of Neurosurgery, Stanford University Medical Center, Stanford, California;
2. 2Departments of Neurosurgery and
3. 3Neuroradiology, University of Berne, Inselspital, CH-3010 Berne, Switzerland; and
4. 4Department of Neurosurgery, Medical University of Graz, A-8036 Graz, Austria