Tumors of the central nervous system have previously been classified according to the WHO classification as follows:
| WHO grade | Grade description | Diagnoses (exemplary) |
| I | Benign (benign) tumors that can usually be cured by surgical removal | Craniopharyngeoma, neurinoma, oligodendroglioma, pilocytic astrocytoma,subependymal giant cell astrocytoma,meningiomas* (80% of all meningiomas are considered benign) |
| II | Benign (malignant) but often infiltrative tumors that are prone to recurrence but do not significantly limit survival | Low-grade gliomas: Astrocytoma (variants: fibrillar, protoplasmic, gemistocytic); atypical meningioma (variants: clear cell, chordoid), diffuse astrocytoma, ependymoma (II/III), oligodendroglioma, anaplastic oligoastrocytoma, pleomorphic xanthoastrocytoma,pilomyxoid astrocytoma |
| III | Malignant tumors associated with a reduction in survival time | Gliomas: anaplastic astrocytoma, ependymoma (II/III), mixed gliomas (II/III), anaplastic oligodendrogliomas; anaplastic meningioma (variants: papillary, rhabdoid), plexus carcinoma |
| IV | Extremely malignant tumors associated with a marked reduction in survival unless effective treatment is available | Glioblastomas (variants: gliosarcoma, giant cell glioblastoma), medulloblastoma |
* The methylation pattern of tumor cells gives an indication of how aggressive a meningioma is. This allows reliable differentiation between safely benign tumors, for which surgery is usually sufficient, and those for which the patient requires additional radiotherapy (radiation therapy).
In addition to histology, the localization of the tumor, especially for complete neurosurgical removal, is of great importance for the prognosis. Other factors include response to radiotherapy or chemotherapy.
The new WHO classification of central nervous system (CNS) tumors considers:
- Histologic assignment of the tumor to a tumor type,
- Histological determination of malignancy criteria. WHO grade is defined on the basis of histological features,
- Determination of molecular genetic parameters with diagnostic, prognostic or predictive value,
- Integrative diagnosis taking into account the 3 aforementioned levels of diagnosis.
