Spss v 20.0 statistical software system

Statistical analyses were performed with non-parametric tests. The interdependence of variables was evaluated by a Spearman non-parametric correlation test. The dependence of Expanded Disability Status Scale (EDSS) scores on different variables was evaluated using linear regression analysis. All statistics reporting differences between anatomical structures or lesions were calculated from one mean value per anatomical structure or lesion per patient. Differences between two groups were assessed with Wilcoxon Mann–Whitney U tests. In cases of multiple testing, significant values were corrected with Holm–Bonferroni method or Shaffer's procedure, as appropriate. Differences in the incidence of perivascular cuffs were assessed with Fisher's exact tests. SPSS V.20.0 statistical software system (IBM Corporation, Armonk, New York, USA) was used for calculations. The reported p values were the result of two-tailed tests; p values smaller or equal to 0.050 were considered statistically significant.