1. *Centre for Pathology and Molecular Medicine, School of Postgraduate Medicine, Keele University, Central Pathology Laboratory, North Staffordshire Hospital, Stoke-on-Trent, Staffordshire, U.K.
2. Department of Neurosurgery, North Staffordshire Hospital, Stoke-on-Trent, Staffordshire, U.K.
3. Department of Mathematics, University of Keele, Keele, Staffordshire, U.K.