The development of targeted therapies for malignant gliomas infiltrating the brainstem has been hampered by the absence of biological data. It is therefore crucial to better understand the biology of these tumours. Despite the safety of the biopsy in brainstem tumours, most teams of paediatric neurosurgery limit the use of stereotactic biopsy only for clinically or radiologically unusual forms. Until recently, there has been no systematic genetic study at diagnosis to date and the few available data were confounded by the inclusion of autopsies or clinically and radiologically unusual cases (Louis, 1993; Gilbertson 2003; Okada, 2008; Zarghooni 2010; Broniscer, 2010; Wu, 2012 and Schwartzentruber, 2012).