1. The Bone Tumour Unit The Royal National Orthopaedic Hospital, Brockley Hill, Stanmore, Middlesex HA7 4LP, UK.
2. The National Hospital for Neurology and Neurosurgery, Queen Square, London WC1N 3BG, UK.
3. Neurosurgical Department The Royal London Hospital, Whitechapel, London E1 1BB, UK.