The Children's Cancer and Leukaemia Group guidelines for the diagnosis and management of dysembryoplastic neuroepithelial tumours.

Dysembryoplastic neuroepithelial tumours (DNETs) were incorporated into the new World Health Organization classification of brain tumours as part of the group of glioneuronal tumours in 1993. Large series of patients with DNETs and pharmaco-resistant epilepsy have been reported. DNETs are most often located in the temporal lobe, occurring in both mesial and lateral temporal locations. DNETs have also been reported in the insular cortex, brain stem, cerebellum, occipital lobe and striatum. Approximately 40% of DNETs are cystic, and solitary nodular, multinodular or diffuse forms have been recognized. Approximately 30% of DNETs are associated with subtle cortical dysplastic changes in the adjacent cortex. DNET nodules usually look like oligodendroglioma, whilst between the nodules it may be possible to recognize vertical columns of neurons surrounded by oligodendrocyte-like cells. Cytologically, oligodendroglial-like cells of DNETs are distinguished from oligodendroglioma by larger nuclei with frequent nuclear indentations and multiple, small nucleoli, whilst oligodendrogliomas consistently show nuclear roundness with one or two occasional nucleoli. Very rare cases of malignant transformation have been reported. DNETs are hypodense on CT and demonstrate decreased signal on the T1-weighted images and a hyper-intense signal on T2-weighted MRI. DNETs associated with pharmaco-resistant epilepsy should be removed early to achieve seizure freedom and prevent tumour progression. The surgical approach should be that of an extended lesionectomy, i.e. excision of the lesion and the abnormal dysplastic cortex around it. Use of MRI-based image guidance (neuronavigation) as a surgical tool to identify this area of abnormal cortex is very helpful to ensure that the extended lesionectomy includes any visibly dysplastic cortex. It is not advocated to use a stereotactic biopsy only, as this may generate an unrepresentative tissue sample consisting of an oligodendroglial component only and may lead to an incorrect diagnosis.