Alice Métais

1 Introduction Extraventricular neurocytoma (EVN) is a rare neuroepithelial tumour that historically has been defined histologically by its resemblance to central neurocytoma while arising outside the ventricular system. In the pre-molecular era, this anatomical distinction, together with shared morphologic features such as uniform round cells, a neuropil-like background, and synaptophysin expression, formed the basis of its classification.

INTRODUCTION FGFR-fused central nervous system (CNS) tumours are rare; they account for 6.1% (n = 29/1000) of paediatric low-grade gliomas (LGG) according to Ryall et al. [1]. They are mainly encountered in the paediatric population, adolescents or young adults. On histology, they are characterised by an oligodendroglioma-like phenotype [2, 3].