[1] Addenbrookes Hosp, Div Neurosurg, Cambridge, England
[2] Univ Cambridge, Cambridge, England
[3] Royal Victoria Infirm, Dept Neurosurg, Newcastle Upon Tyne NE1 4LP, Tyne & Wear, England
[4] Newcastle Univ, Newcastle Upon Tyne NE1 7RU, Tyne & Wear, England
[5] Queen Elizabeth Hosp, Dept Neurosurg, Birmingham B15 2TH, W Midlands, England
[6] Univ Birmingham, Birmingham, W Midlands, England
[7] Western Gen Hosp, Dept Neurosurg, Edinburgh EH4 2XU, Midlothian, Scotland
[8] Univ Edinburgh, Edinburgh, Midlothian, Scotland