At present, diagnosis of oligodendroglioma is made on histological and radiographic criteria in the French Mayo-Ste Anne classification. The less frequent grade A oligodendrogliomas are characterized by no vascular contrast on RMN evaluation comparatively to grade B forms. This benign histological subtype relapses in few cases with a more aggressive histology. To determine these relapsed cases at diagnosis, a collection of tumour begun in February 2004. Then, our study was designed to identify diagnostic molecular and metabolic markers that could eventually be used as a signature characterising grade A versus grade B oligodendrogliomas. The molecular analysis will use genomic techniques like allelotyping study, quantitative real-time PCR, gene sequencing , serial analysis of genomic expression and immunohistochemistry, since the metabolic study will be the spectroscopic examination of in vivo tumour. This study will include paediatric and adult patients followed for oligodendrogliomas, medulloblastomas and gliomas to compare the different tumour signatures. All these results will be correlated to survival and clinical features.