[1] Addenbrookes Hosp, Dept Clin Neurosci, Div Neurosurg, Cambridge, England
[2] Univ Cambridge, Cambridge, England
[3] James Cook Univ Hosp, Div Neurosurg, Middlesbrough, Cleveland, England
[4] Newcastle Univ, Neurosurg Trials Unit, Newcastle Upon Tyne, Tyne & Wear, England
[5] Western Gen Hosp, Div Neurosurg, Edinburgh EH4 2XU, Midlothian, Scotland
[6] Univ Edinburgh, Edinburgh, Midlothian, Scotland