Niklas Lützen1, Anna Zeitlberger2, Jürgen Beck2, Horst Urbach3. 1. Dept. of Neuroradiology, Medical Center. University of Freiburg, Breisacher Str. 64, 79106, Freiburg, Germany. niklas.luetzen@uniklinik-freiburg.de. 2. Dept. of Neurosurgery, Medical Center. University of Freiburg, Freiburg, Germany. 3. Dept. of Neuroradiology, Medical Center. University of Freiburg, Breisacher Str. 64, 79106, Freiburg, Germany.