With around 3,400 cases per year in France, diffuse gliomas are the most common primary tumours of the central nervous system. Their grade varies from 2 to 4. Whatever the grade, their prognosis is poor, because tumour recurrence is systematic, because no personalised medicine is available for the treatment of these cancers, and because the tools for monitoring recurrence are imperfect. Treatment of diffuse gliomas is based on removal of as much of the tumour as possible, whatever its grade. Surgery is followed by radiotherapy and chemotherapy depending on the grade and quality of the excision. In the event of recurrence, the patient may be offered second-line chemotherapy or further surgery. During and after treatment, patients are regularly monitored by MRI in order to detect any recurrence as early as possible and propose a new treatment. However, for grade 2 and 3 gliomas, MRI monitoring is imperfect because it cannot detect tumour recurrence at an early stage. Initiation of new treatment at the time of recurrence, which is inevitable, is therefore often delayed, which is harmful for patients. It is therefore vital to identify a reliable, easy-to-use and non-invasive biomarker that can be used to monitor patients undergoing surgery for grade 2 and 3 diffuse gliomas, and thus enable earlier diagnosis of recurrence. These biomarkers could be microRNAs. MicroRNAs are small non-coding RNAs involved in the regulation of genes and, consequently, of the intracellular signalling pathways that govern cell behaviour. They are therefore widely implicated in oncogenesis, and in particular in the mechanisms that promote tumour migration, invasion and proliferation. Several preliminary studies have shown that serum levels of pro-oncogenic microRNAs correlate with tumour rates in gliomas. No study has investigated the possibility of using them to detect tumour recurrence earlier in grade 2 and 3 gliomas. With this study, the investigators hope to use pro-oncogenic microRNAs to monitor glioma patients and diagnose early recurrence in grade 2 and 3 gliomas.