[1] Natl Univ Singapore, Yong Loo Lin Sch Med, 1E Kent Ridge Rd,Level 11, Singapore 119228, Singapore
[2] Univ Bristol, Bristol Med Sch, Fac Hlth Sci, Bristol, Avon, England
[3] Natl Univ Hlth Syst, Div Neurosurg, Dept Surg, Natl Univ Hosp, Singapore, Singapore
[4] Natl Neurosci Inst, Dept Neurosurg, Singapore, Singapore