Classification of Primary Brain Tumors: Molecular Aspects

The guiding principle of this chapter is the importance of combining traditional morphological data with the recently acquired knowledge on the genetic and epigenetic signalling pathways which drive the evolution of CNS tumors. The official World Health Organization terminology (WHO, 2007) will be used since it is the source of information for neurooncology, neuroradiology, neurosurgery, etc. It is of outmost importance that new entities have emerged since 2007 and it seems inevitable to see a new classification in the near future. It is beyond the scope if this chapter to dwell on the pitfalls in diagnostic surgical neuropathology, suffice is to say that the classic, traditional case descriptions which are usually presented in textbooks comprise only a fraction of diagnostic dilemmas so often hunting practicing neuro-oncopathologists. The main focus will be placed on intracranial lesions but it needs to be emphasized that the diagnostic entities which come the way of a surgical neuropathologist broadly overlap with an extensive range of entities which basically belong to hematopathology, soft tissue and bone/chondroid tumors. In all textbooks on neuropathology the usual way to start is to point out that knowledge of brain and spinal cord anatomy as well as familiarity with the broad range of cellular reactions in diseased CNS are essential for success in understanding pathology reports. There is no way to cover all these details, hence a list of reference books is provided. This chapter is born out of the need to outline unambiguous and consistent terminology of brain tumors. This together with a strong urge to define the use of a universally accepted grading system (be that weak as it is despite of century-old efforts) could help not only all specialists who are involved in treating brain tumor patients but also and of outmost importance the patients themselves.