Panagiotis Kokkalis1, Christos Chamilos1, Spyros Sgouros2. 1. "Mitera" Children's Hospital, University of Athens, Athens, Greece. 2. Department of Pediatric Neurosurgery, "Mitera" Children's Hospital and "National and Kapodistrian" University of Athens, Erythrou Stavrou 6, Marousi, 151 23, Athens, Greece. sgouros@med.uoa.gr.