1. Department of NeurosurgeryUniversity Hospital Virgen del Rocío Sevilla Spain
2. Department of NeurosurgeryUniversity Hospital of Leon Leon Spain
3. Department of Neurological SurgeryUniversity of Pittsburgh Medical Center Pittsburgh PA U.S.A.
4. Department of OtolaryngologyUniversity of Pittsburgh Medical Center Pittsburgh PA U.S.A.
5. Department of NeurosurgeryStanford University Medical Center Palo Alto CA U.S.A.