Dysembryoplastic neuroepithelial tumour is a benign, mixed neuronal-glial tumour typically presenting in children and young adults with a history of long-standing seizures, characteristically appearing as a temporal lobe cortical lesion exhibiting a bubbly appearance on MRI.
Description
Dysembryoplastic neuroepithelial tumour (DNET) is a benign, mixed glioneuronal tumour commonly located within the cerebral cortex. It’s most notable for its association with drug-resistant partial seizures in children and young adults.
Pathogenesis
The precise pathogenesis of DNET is not entirely understood. It is hypothesised to arise from aberrant neuronal and glial precursor cells during cortical development, resulting in a mixed glioneuronal tumour.
Subtype
- Simple Form: Predominantly composed of a specific glioneuronal element, commonly presents as a solitary lesion.
- Complex Form: In addition to the specific glioneuronal element, it presents with other cortical dysplasia features.
- Non-specific Form: Lacks a specific glioneuronal element, displays characteristics of cortical dysplasia.
Epidemiology, Risk Factors & Associations
- Commonly diagnosed in children and young adults (average age at diagnosis: 10-20 years).
- Associated with long-standing, drug-resistant partial seizures.
Clinical Features
- Seizures are the most common presenting symptom.
- Focal neurological deficits based on the tumour location may occur but are less common.
Complications
- Intractable epilepsy.
- Cognitive and behavioural problems related to long-standing epilepsy.
Pathological Features
Histopathology
- Macroscopic: Typically well-circumscribed, non-invasive lesions within the cortical grey matter.
- Microscopic: Characterised by a specific glioneuronal element, appearing as clusters of floating neurons within a mucinous matrix.
Serology
No specific serological markers.
Biochemistry
No specific biochemical markers.
Radiological Features
General Features
- Characteristic well-defined, cortical-based lesion which shows minimal or no mass effect or perilesional oedema, reflecting slow-growing nature and its tendency to expand rather than infiltrate local structures.
- The lesion has a cortical base and an apex pointing towards the lateral ventricle
- Can occur in any lobe but there is a predilection for the temporal lobes
- Calcifications rarely associated with DNETs (<5% of cases).
CT
- Non-contrast: Typically appears as an iso- to hypodense lesion, corresponding to the mixture of neuronal and glial elements. Scalloping of overlying bone maybe seen.
- Contrast-enhanced: There is minimal or no enhancement post-contrast administration, highlighting the non-aggressive nature of DNET.
MRI
- T1 – Iso- to hypointense compared to the surrounding brain parenchyma, a reflection of its mixed cellular composition.
- T2: Homogenously hyperintense soap bubble appearance with delicate septa-like structures
- FLAIR: Partial suppression of bubble appearance, producing bright rim sign, which is a high signal rim on the periphery of the tumour (representing the mucinous matrix surrounding the neoplastic nodules)
- T1 C+: Shows minimal or no enhancement, aligning with its benign nature.
- DWI/ADC: No restricted diffusion (very high ADC values are measured inside the mass)
- SWI: No susceptibility
Grading and Staging
DNETs are classified as WHO Grade I tumours, reflecting their benign nature. No specific staging system exists for these tumours.
Diagnosis
Diagnosis is typically based on characteristic imaging findings and the clinical context of long-standing, drug-resistant epilepsy. Definitive diagnosis is confirmed histologically following surgical resection.
Differential Diagnosis
- Ganglioglioma: Another cause of long-standing epilepsy. Usually a cyst with a strongly enhancing mural nodule and frequent calcifications.
- Focal cortical dysplasia: Shares clinical features with DNET but lacks the ‘bright rim’ sign on T2WI.
- Low-grade glioma: May have similar imaging features, but usually demonstrates mass effect or surrounding oedema, which are uncommon in DNET.
Management
The primary management of DNET is surgical resection, aimed at achieving seizure freedom. Given the benign nature of the tumour, no adjuvant therapy is typically required post-resection.