1 Perelman School of Medicine, University of Pennsylvania, Philadelphia, USA.
2 Department of Neurosurgery, University of Pennsylvania, Philadelphia, USA.
3 Department of Neurosurgery, Thomas Jefferson University, Philadelphia, USA.
4 Division of Neurosurgery, Children's Hospital of Philadelphia, Philadelphia, USA.
5 Perelman School of Medicine, University of Pennsylvania, Philadelphia, USA; Department of Neurosurgery, University of Pennsylvania, Philadelphia, USA.
6 Perelman School of Medicine, University of Pennsylvania, Philadelphia, USA; Department of Neurosurgery, University of Pennsylvania, Philadelphia, USA; Division of Neurosurgery, Children's Hospital of Philadelphia, Philadelphia, USA. Electronic address: KENNEDYBC@chop.edu.