Dysembryoplastic neuroepithelial tumours (DNETs) are low-grade glioneuronal tumours strongly associated with focal epilepsy, particularly in children and young adults. They are usually slow-growing, but their main clinical burden is often recurrent seizures rather than tumour mass effect.
Where DNETs occur
DNETs are usually cortical and commonly occur in the temporal lobe, although other cortical locations are possible. MRI often shows a well-circumscribed, multicystic or “bubbly” cortical lesion with little surrounding oedema or mass effect.
Epilepsy presentation
Focal seizures are typical and may become drug-resistant. Long delays between seizure onset and definitive treatment have historically occurred because the tumour itself can appear indolent.
DNET and focal cortical dysplasia
DNET can coexist with focal cortical dysplasia. This matters because seizure-generating tissue may extend beyond the visible tumour in some patients.
Diagnosis
Diagnosis uses MRI, clinical presentation and histopathology. Molecular findings, including alterations involving FGFR1 and other signalling pathways, have improved understanding of these tumours.
Surgery and seizure outcome
Surgery is often considered when seizures are drug-resistant or when the lesion requires diagnostic clarification. Reviews have consistently found high rates of seizure freedom after complete resection, although outcomes vary and depend on lesion location, completeness of treatment and the surrounding epileptogenic network.
Not every cortical lesion is a DNET
Other low-grade epilepsy-associated tumours, focal cortical dysplasia and some gliomas can resemble DNET radiologically. Expert neuroradiology and pathology are important.
Follow-up
DNETs are generally indolent. Recurrence is uncommon but can occur, particularly after incomplete resection. Long-term follow-up is tailored to the individual.
Related reading
- Brain Tumour-Related Epilepsy
- Focal Cortical Dysplasia
- MRI and Neuroimaging in Epilepsy
- Epilepsy Surgery
What makes DNET distinctive
Dysembryoplastic neuroepithelial tumours are low-grade, epilepsy-associated glioneuronal tumours that usually arise in the cerebral cortex of children or young adults. They are typically slow-growing and often discovered during investigation of focal seizures.
Seizures may begin years before diagnosis
Because DNETs can be indolent, epilepsy may be the only symptom for a long period. MRI commonly shows a cortically based, multinodular lesion with little mass effect.
The epileptogenic zone may extend beyond the tumour
Seizures can arise from tumour, adjacent dysplastic cortex or a wider network. This helps explain why complete lesionectomy alone is sufficient in some people but broader tailored resection is needed in others.
Surgical outcomes
Seizure outcomes are generally favourable after complete resection, particularly when surgery is not excessively delayed. Preserving eloquent cortex remains essential, and intraoperative or invasive electrophysiology may be used in selected cases.
Oncological behaviour
Classic DNET is usually WHO grade 1 and malignant transformation is rare. Follow-up is individualised according to pathology, extent of resection and imaging behaviour.
Sources and further reading
- Dysembryoplastic Neuroepithelial Tumors: What You Need to Know. 2019. PMID: 30981794.
- Dysembryoplastic Neuroepithelial Tumor: A Benign but Complex Tumor of the Cerebral Cortex. 2022. PMID: 35929111.
- Surgical outcomes and prognostic factors in epilepsy associated with low-grade brain tumors: a systematic review. 2026. PMID: 41680353.
Evidence checked: September 2026.