Other / Other / MRI

Dysembryoplastic neuroepithelial tumor (DNET)

Young patient (typically child or adolescent, most before age 20) presenting with focal seizures that progress to chronic drug-resistant epilepsy; DNET is a long-term epilepsy-associated tumor accounting for ~5.9% of specimens from epilepsy surgery.

Key Images

A and B: T1-weighted and T2-weighted magnetic resonance images of a 10-year-old girl who presented with recurrent focal seizures. A multinodular mass is located in the right middle frontal gyrus. C and D: T2-weighted axial and coronal images of a 12-year-old boy who came to the clinic for chronic epilepsy. A large tumor is situated in the insular and left inferior frontal lobes. There are several satellite lesions (yellow arrows) on the medial side of the mass, in the caudate nucleus and internal capsule.
A and B: T1-weighted and T2-weighted magnetic resonance images of a 10-year-old girl who presented with recurrent focal seizures. A multinodular mass is located in the right middle frontal gyrus. C and D: T2-weighted axial and coronal images of a 12-year-old boy who came to the clinic for chronic epilepsy. A large tumor is situated in the insular and left inferior frontal lobes. There are several satellite lesions (yellow arrows) on the medial side of the mass, in the caudate nucleus and internal capsule.
DNET
DNET
Floating Neurons
Floating Neurons
Diagnostic criteria for DNET (according to the 2021 WHO classification). DNET, dysembryoplastic neuroepithelial tumor
Diagnostic criteria for DNET (according to the 2021 WHO classification). DNET, dysembryoplastic neuroepithelial tumor
DNET
DNET
DNET
DNET
DNET
DNET
A–G male, 8 years old, with DNET in the left basal ganglia. A. T1WI left basal ganglia tumor showed iso- and low mixed signal; B. T2WI tumor showed iso- and slightly high and low mixed signal; C. FLAIR tumor showed iso- and slightly high mixed signal; D. DWI tumor showed iso- and low mixed signal; E. ADC diagram tumor showed high signal intensity; F. enhanced MRI of tumor showed annular enhancement; G. pathological images showed that the tumor tissue was formed by abundant mucous matrix and microcapsules. The morphology was similar to astrocytes and oligodendrocytes, and a few neurons were seen with slightly increased number of glial cells (
A–G male, 8 years old, with DNET in the left basal ganglia. A. T1WI left basal ganglia tumor showed iso- and low mixed signal; B. T2WI tumor showed iso- and slightly high and low mixed signal; C. FLAIR tumor showed iso- and slightly high mixed signal; D. DWI tumor showed iso- and low mixed signal; E. ADC diagram tumor showed high signal intensity; F. enhanced MRI of tumor showed annular enhancement; G. pathological images showed that the tumor tissue was formed by abundant mucous matrix and microcapsules. The morphology was similar to astrocytes and oligodendrocytes, and a few neurons were seen with slightly increased number of glial cells (
Look For First
  • Cortical-based multinodular or 'bubbly' appearance in a young patient with epilepsy
  • T2/FLAIR hyperintense lesion with little to no gadolinium enhancement
  • Temporal lobe location (most common), but can occur anywhere in cerebral cortex
Key Image Findings
  • MRI is primary modality; CT shows hypoattenuating cortical and subcortical lesion with indolent imaging behavior.
  • Characteristic multinodular or multicystic 'bubble-like' or 'popcorn-like' appearance reflecting the underlying nodular intracortical architecture.
  • T1 hypointensity and T2/FLAIR hyperintensity, typically with absent or minimal gadolinium enhancement; patchy or partial enhancement can occur in some cases.
  • Cortical and subcortical white matter involvement, often extending along an entire gyrus or wedge-shaped portion of a lobe, with variable morphology across multiple gyri.
  • Chassoux classification recognizes three imaging patterns: Type 1 (polycystic), Type 2 (nodular), and Type 3 (diffuse/dysplastic), which may correlate with epileptogenic zone and seizure outcome.
  • Satellite lesions present in approximately 50% of cases, typically appearing as small separate nodules located on the medial/deep aspect of the primary tumor separated by thin white matter, potentially extending toward caudate, internal capsule, or ventricular margin.
  • Associated focal cortical dysplasia may surround the tumor, particularly in complex-type DNET, extending the epileptogenic zone beyond tumor boundaries.
  • Poorly defined margins on T2/FLAIR imaging can make complete surgical assessment challenging, especially when satellite lesions are adjacent to eloquent cortex or white-matter tracts.
Differential Diagnosis
  • Ganglioglioma: usually shows small cystic lesion with mural/nodular component rather than multinodular/multicystic pattern; demonstrates strong gadolinium enhancement in ~50% of cases (vs. minimal enhancement in DNET); ¹¹C-methionine PET shows increased uptake in ganglioglioma but low metabolic activity in DNET.
  • Focal cortical dysplasia: lacks the distinct glioneuronal columns and floating neurons; imaging alone may not definitively distinguish from DNET, particularly complex-type DNET with surrounding dysplasia.
  • Low-grade glioma: typically less cortically based and less epileptogenic; imaging pattern and clinical presentation favor DNET.
  • Cavernous malformation: shows characteristic 'popcorn' calcification pattern and hemosiderin ring; lacks multinodular glioneuronal architecture.
  • Cystic neoplasm with enhancement: strong enhancement and cystic-nodular morphology favor ganglioglioma over non-enhancing DNET.
Discussion

DNET represents ~1.5% of all childhood brain tumors and ~30% of mixed glioneuronal tumors; it is one of the classic long-term epilepsy-associated tumors (LEATs) with pronounced epileptogenicity reflecting both cortical location and developmental/dysplastic nature.

Pathologically, DNET is characterized by multinodular intracortical architecture with glioneuronal columns (axons perpendicular to cortex lined by oligodendroglia-like cells) and floating neurons suspended in a mucin-rich matrix; lacks aggressive features such as mitoses, necrosis, or high cellularity.

Molecularly distinct entity with characteristic FGFR1 alterations (internal tandem duplications, fusions, missense mutations), particularly those affecting the tyrosine kinase domain; modern DNA methylation and transcriptional profiling provide a distinct DNET signature useful for resolving diagnostically difficult cases.

Historically considered benign with acceptable incomplete resection, but recent evidence shows residual tumor—especially satellite nodules—can slowly enlarge; approximately 36% recurrence/progression rates reported in some series, higher than historically believed.

Gross total resection is the major determinant of both long-term tumor control and seizure freedom (~60–80% seizure-free after complete resection), making satellite nodule identification and complete removal critical for optimal outcomes.

Breakthrough seizures after initial control may signal tumor progression or satellite lesion enlargement; surgical planning must balance complete removal against avoiding injury to eloquent cortex, corticospinal tract, and optic radiations.

Reporting Pearls

Describe the lesion as a 'cortical-based multinodular/multicystic lesion with T2/FLAIR hyperintensity and minimal enhancement, consistent with DNET'; always specifically search for and comment on the presence or absence of medial/deep satellite nodules, as their identification significantly impacts surgical planning and long-term outcome—document their number, location relative to eloquent cortex, and relation to white-matter tracts.

Pitfalls
  • Overlooking satellite lesions on initial imaging review; systematically evaluate the medial/deep margin and white matter adjacent to the primary tumor, as satellite nodules are present in ~50% of cases and are crucial for surgical planning.
  • Overestimating the enhancement pattern; minimal or patchy enhancement is typical for DNET—do not be misled into favoring ganglioglioma if focal enhancement is present.
  • Underestimating the significance of residual tumor; historical literature emphasized acceptability of incomplete resection, but modern evidence shows residual lesions including satellites can enlarge and compromise seizure freedom; always emphasize completeness of resection in reporting.
  • Confusing DNET with focal cortical dysplasia based on imaging alone, particularly in complex-type DNET with surrounding dysplastic cortex; integration of imaging features (multinodular pattern, glioneuronal architecture on pathology, FGFR1 molecular signature) and clinical context is necessary for accurate diagnosis.
Source: Reference source