116th Meeting of the British Neuropathological Society Institute of Child Health, London

Long-term epilepsy-associated tumours(LEATs) are typically low grade and often glioneuronalin nature. Controversial and newer entities notincluded in the current WHO classification include thediffuse DNT and nodular vacuolated neuronal tumour(VNT). The differential diagnosis of LEATs ranges fromdiffuse gliomas to malformations. Point mutations ofthe BRAF gene (V600E mutations) have been shownin a range of glioneuronal tumours, such as PXA, gangliogliomas,desmoplastic infantile gliomas as a diagnosticallyuseful test. We investigated BRAF mutationsin a range of LEATs including these newer and controversialentities.Material and methods: We included 38 cases; 15 diffuseDNT, 5 VNT, 7 gangliogliomas, 8 complex DNT and 3FCD type IIB cases. All of the patients have given consentfor research and the project has ethical approval.In each case sections were taken of the tumour, themore cellular areas micro-dissected and sequencing forBRAF mutation carried out in addition to immunostaningfor BRAF mutation. The findings were correlatedwith clinical and pathological features.Results: There were no mutations detected in the typicalDNT, VNT or FCD IIB group but they were identified in28% of the diffuse DNT group and 33% of GG group. AllBRAF mutated cases were in the temporal lobe and alltumours were CD34 positive. All cases with confirmedBRAF mutations were positive with BRAF immunohistochemistry,with patchy labeling of glial in addition toneuronal elements. Positive immunolabeling was alsoseen in a few cases negative for the V600E mutation.Conclusion: In this small series the incidence of confirmedBRAF mutation in ganglioglioma and diffuseDNT was similar which could support that these entitiesare related. Immunohistochemistry for BRAF mutationmay prove a specific and a more sensitive methodof detection in these tumours which comprise mixedtumour and normal cell populations