1 Department of Neurosurgery, North Bristol University Hospital, Bristol, UK.
2 Department of Neurosurgery, North Bristol University Hospital, Bristol, UK; Department of Neurosurgery, University of Tennessee Health Sciences Center, Memphis, Tennessee, USA.
3 Department of Neurosurgery, North Bristol University Hospital, Bristol, UK; Department of Neurosurgery, Stanford University, Stanford, California, USA. Electronic address: [email protected].