Dysembryoplastic neuroepithelial tumor (DNET)
General description
Dysembryoplastic neuroepithelial tumor (DNET) is a rare, benign mixed glioneuronal neoplasm classified as WHO Grade I that predominantly affects children and young adults. Disease onset occurs before the age of 20 years in 90% of patients, with the mean age of seizure onset being 8.1 years old in children. The mean age at diagnosis ranges from 9-15.8 years across various studies, though cases can occur at any age from infancy to the fifth decade of life.
DNET belongs to the category of long-term epilepsy-associated tumors (LEATs) and is classified under neuronal and mixed neuronal-glial tumors in the WHO classification system. An association with Noonan syndrome has been proposed in some cases.
The vast majority of DNET patients (90%) present with longstanding treatment-resistant focal epilepsy without associated or progressive focal neurological deficits. Complex partial seizures account for 81.3-86.4% of seizure presentations, typically beginning in childhood with a mean duration of seizures prior to surgical intervention ranging from 3.2 to 4.8 years.
References
- Varlet, P., et al. "Dysembryoplastic neuroepithelial tumors: CT, MR findings and imaging follow-up: a study of 53 cases." Journal of Neuroradiology= Journal de Neuroradiologie 28.4 (2001): 230-240.
- Parmar, Hemant A., et al. "Fluid-attenuated inversion recovery ring sign as a marker of dysembryoplastic neuroepithelial tumors." Journal of computer assisted tomography 31.3 (2007): 348-353.
Subcortical mass
DNET originates within the brain parenchyma as an intrinsic cortical or cortico-subcortical lesion. The vast majority are centered in cortical gray matter of the temporal lobe, arising from secondary germinal layers. All tumors demonstrate intracortical or subcortical locations, with the cortex being involved in all cases and subcortical white matter involvement occurring in approximately 60% of cases.
DNET demonstrates characteristic morphological features with well-demarcated margins in the majority of cases. Well-demarcated lobular tumor margins are observed in approximately 80% of cases.
Solid component of DNET demonstrates hypointense on T1-weighted images, while, on T2-weighted and FLAIR images, DNET exhibits hyperintense signal intensity in nearly all cases. Contrast enhancement in DNET is variable but generally minimal. Enhancement occurs in approximately 20-30% of cases. Diffusion-weighted images and ADC mapping show no restricted diffusion.
The characteristic soap bubble appearance on T2-weighted images represents a multi-loculated pseudocystic pattern that is highly characteristic of DNET.
The hyperintense ring sign, also known as the bright rim sign, represents a well-defined rim of high signal around the tumor on FLAIR sequences. This hyperintense ring, whether complete or incomplete, demonstrates 82% sensitivity and 90% specificity for DNET diagnosis.
Calcification represents a relatively common finding in DNET, occurring in approximately 30-36% of cases based on imaging studies.
One of the distinguishing features of DNET is the consistent absence of significant surrounding vasogenic edema. Necrosis is not also a feature of typical DNET, with no cases of necrosis reported in histopathological examination.