1. Department of Neurosurgery, Center for Advanced Neurology and Neurosurgery, Porto Alegre, Rio Grande do Sul, Brazil
2. Department of Anatomy, Federal University of Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil
3. Department of Neurology, Instituto do Cérebro (INCER), Pontifical Catholic University of Rio Grande do Sul, Porto Alegre, Rio Grande do Sul, Brazil
4. Department of Neurosurgery, Hospital das Clínicas, Faculty of Medicine, University of São Paulo, São Paulo, Brazil.