Dysembryoplastic neuroepithelial tumours are WHO grade 1 glioneuronal tumours mostly seen in children and young adults with a long history of seizures as a cortically-based temporal lobe lesion with a bubbly, multicystic appearance on imaging and a characteristic specific glioneuronal element on histology.
Description
Dysembryoplastic neuroepithelial tumour is a rare, benign brain tumour classified under the category of glioneuronal tumours. It is most commonly associated with chronic epilepsy and is characterised by its indolent behaviour and excellent prognosis after surgical resection.
Pathogenesis
DNET is believed to arise from abnormal neuronal and glial differentiation during cortical development, which explains its frequent association with epilepsy and its typical occurrence in children and young adults.
Subtypes
DNETs are primarily classified based on histological features into:
- Simple form: Characterised by specific glioneuronal elements and absence of atypical cells.
- Complex form: Includes specific glioneuronal elements with areas of cortical dysplasia.
Epidemiology, Risk Factors & Associations
- Predominantly occurs in children and young adults, with no clear gender predilection.
- Strongly associated with early-onset epilepsy.
- No known risk factors or familial predisposition.
Clinical Features
- Long-standing history of seizures, often drug-resistant focal seizures.
- Rarely presents with signs of increased intracranial pressure or neurological deficits.
- Typically, patients have a normal neurological examination.
Complications
- Chronic epilepsy, which can impact quality of life and cognitive development.
- Potential for psychological and educational difficulties due to longstanding epilepsy.
Pathological Features
Histopathology
- Macroscopic: Well-circumscribed, cortically-based lesion with a multinodular bubbly appearance.
- Microscopic: Mixture of neuronal and glial components with specific “floating” neurons in a mucoid matrix.
Radiological Features
General Features
- Cortically based lesion with a bubbly appearance
- Most commonly located in the temporal lobe (65%). Other locations include;
- Frontal lobe (20%)
- Caudate nucleus
- Cerebellum
- Pons
CT
- Typically hypodense to isodense cortical lesion without significant mass effect.
- No or minimal enhancement
- Calcification may be present
- May remodel the inner table of the skull vault over time without erosion.
MRI
- T1: Isointense to slightly hypointense compared to the surrounding cortex.
- T2/FLAIR: Hyperintense signal with a multicystic or bubbly appearance.
- T1 Gad+: Minimal to no enhancement.
- DWI/ADC: Does not show restricted diffusion.
Grading and Staging
- DNETs are WHO Grade I lesions, indicating a benign prognosis.
Diagnosis
- Based on clinical presentation of long-standing epilepsy and characteristic MRI features.
- Histopathological examination after surgical resection confirms the diagnosis.
Differential Diagnosis
- Multinodular and vacuolating neuronal tumour (MVNT) – Seen in the juxtacortical white matter, rather than cortex.
- Ganglioglioma: Another temporal lobe tumour causing epilepsy, which may show more pronounced enhancement. Does not exhibit multicystic appearance.
- Cortical dysplasia: Lacks the discrete “bubbly” architecture seen in DNET.
- Low-grade gliomas: May have a more aggressive appearance and different histological features.
Management
- Surgical resection is the treatment of choice, often leading to seizure freedom.
- Complete resection is usually curative, given the tumour’s benign nature.
- Postoperative follow-up with MRI to ensure complete resection.
- Management of epilepsy with antiepileptic drugs pre- and post-operatively, with the goal of medication reduction or cessation following successful surgery.