"A possibility of systematisation of cns-tumours is the distinction regarding the cellular origin, the cell composition and growth behavior, on which the classification of the World Health Organization (WHO) is based. The latest version dates from 2007, which established - compared to previous versions - mostly a precise adjustment of the diagnosis and which is only in some cases a complete makeover. Particularly, three innovations were identified within the revision: new tumour entities, new variants of already defined entities and new differentiation patterns of known tumours without clinical or genetic characteristics. According to the WHO, four different tumour grades are distinguished. This assessment is based on neuropathological, anatomical, histological and genetic characteristics of tumours. The evaluation of the tumour tissue under the microscope plays an important role."