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| Untersuchte Arbeit: Seite: 9, Zeilen: 2-21 |
Quelle: Waelzlein 2007 Seite(n): 11, Zeilen: 15ff |
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| 1.1. Brain tumors and their classification
Glia cells are the most common cell type in the brain and make up 90 % of the total cell number (Kettenmann, H et al, 1995) depending on species. They were discovered by Virchow (1856), who described them as Nervenkitt, a kind of glue for neurons (gr. glia: glue). Initially, they were considered as merely supporting cells for neurons, yet recently they were shown to fulfill a range of far more complex functions. The group of glia cells consists of astrocytes, oligodendrocytes and Schwann cells (Kettenmann, H et al, 1995). Historically, brain tumors were thought to consist of transformed glia cells and are therefore called gliomas. Different types of gliomas are astrocytomas, oligodendrogliomas and schwannomas, depending on the preferential type of differentiation of these tumors. Schwannomas often correspond to benign tumors. It is still unknown how these transformations occur and what triggers them. One theory claims that disruptions in the glial cell cycle lead to glioma formation. However, recent research provided more and more evidence that gliomas emerge from neural precursor cells. Gliomas are the most common group of primary tumors in the brain and make up 30 – 40 % of all brain tumors (Kleihues, P et al, 1993). The World Health Organisation (WHO) introduced a classification in 1993, which divides astrocytomas into four malignancy grades: |
1.3. Brain tumours and their classification
Glia cells are the most common cell type in the brain and make up 90 % of the total cell number (37). They were discovered by Virchow (1856), who described them as Nervenkitt, a kind of glue for neurons (gr. glia: glue). Initially, they were considered as merely supporting cells for neurons, yet recently they were shown to fulfill a range of far more complex functions. The group of glia cells consists of astrocytes, oligodendrocytes and Schwann cells (37). Historically, brain tumours were thought to consist of transformed glia cells and are therefore called gliomas. Different types of gliomas are astrocytomas, oligodendrogliomas and schwannomas, depending on the relevant cell type. Schwannomas often correspond to benign tumours. It is still unknown how these transformations occur and what triggers them. One theory claims that disruptions in the glial cell cycle lead to glioma formation. However, recent research provided more and more evidence that gliomas emerge from neural precursor cells (1.2.). Gliomas are the most common group of primary tumours in the brain and make up 30 – 40 % of all brain tumours (40). The World Health Organisation (WHO) introduced a classification in 1993, which divides astrocytomas into four malignancy grades: 37. Kettenmann,H. and Ransom,B. 1995. Neuroglia. Oxford University Press. 40. Kleihues,P., Burger,P.C., and Scheithauer,B.W. 1993. The new WHO classification of brain tumours. Brain Pathol. 3:255-268. |
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