1 Department of Neurosurgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
2 Department of Neurosurgery, Drexel University College of Medicine, Philadelphia, Pennsylvania, USA.
3 Department of Neurosurgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA. Electronic address: jang.yoon@pennmedicine.upenn.edu.