Neurosurgical Service, KK Women's and Children's Hospital, 100 Bukit Timah Road, Singapore 229899, Singapore; Department of Neurosurgery, National Neuroscience Institute, 11 Jalan Tan Tock Seng, Singapore 308433, Singapore; SingHealth Duke-NUS Neuroscience Academic Clinical Program, 11 Jalan Tan Tock Seng, Singapore 308433, Singapore. Electronic address: