[1] Columbia Univ, Dept Neurosurg, New York, NY 10027 USA
[2] Natl Hosp Neurol & Neurosurg, Queen Sq, London, England
[3] Cleveland Clin London, Inst Neurosci, Grosvenor Pl, London, England
[4] Emory Univ, Dept Neurosurg, Atlanta, GA 30322 USA
[5] Grenoble Univ Hosp, Dept Neurosurg, Grenoble, France