Dysembryoplastic neuroepithelial tumor (DNET)

Findings

Brain MRI shows T2 hyper intense lesion in a right parietal cortex with multiple small "cystic" components, extension into subcortical white matter. FLAIR hyperintense, but without perilesional edema or mass effect. No contrast enhancement.


Diagnosis: Dysembryoplastic neuroepithelial tumor (DNET)


Key points

Benign intracortical mass, superimposed on a background of cortical dysplasia.
Typical appearance: small, wedge-shaped "bubbly" mass which is based in a single gyrus, extends towards the ventricle. Characteristic features are a lack of mass effect, surrounding edema, or post-contrast enhancement. There should be little/no growth of the lesion over time.
Frequently scallops inner table of skull, sometimes calcifies, and infrequently hemorrhages. Associated cortical dysplasia is common.
Usually found in children/adolescents, comprises 1-2% of primary brain tumors (age <20). Patients commonly present with partial seizures. Most commonly location is in temporal lobe, followed by parietal cortex, caudate nucleus, septum pellucidum. From 5-80% of epilepsy brain specimens show DNETs.


Radiographic Findings

CT: Thickened gyrus, slightly hypo attenuating. May mimic acute ischemia.
MR: T1 - hypo intense with gyral architectural distortion. T2 - strikingly hyper intense, with bubbly cystic components, extends towards ventricle. FLAIR - characteristic "bright rim," but no perilesional edema. T1+C = minimal / no enhancement. DWI = no diffusion restriction.