Dale Ding1, Robert M Starke2, Maurice Moriarty3, Stefan Brew3. 1. Department of Neurosurgery, University of Virginia, Charlottesville, VA 22908, USA; Department of Neurosurgery, Auckland City Hospital, Auckland 1142, New Zealand. 2. Department of Neurological Surgery, University of Miami, Miami, FL 33136, USA. 3. Department of Radiology, Auckland City Hospital, Auckland 1142, New Zealand.