Dysembryoplastic neuroepithelial tumour (DNET) - non-specific variant
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A small cortical circumscribed bright T2 mass involves the inferior temporal gyrus on the left, without enhancement. It appears to have a small central area of FLAIR signal suppression, surrounded by a T2 bright rim.
The patient went on to have a resection.
Sections show the specimen to contain a low-grade tumour that appears to be relatively circumscribed. The tumour is characterized by varied appearances that range from a more solid fibrillar appearance with numerous Rosenthal fibres, to a less compact pattern with cells that contain clear perinuclear cytoplasm, within a loosely microcystic background. Individual tumour cells display round to elongated nuclei. Nuclear pleomorphism is mild to moderate. Mitotic activity is not increased. Vascular neogenesis and areas of necrosis are not seen. In areas, the tumour is located within superficial cortex, and renders an exophytic appearance. Although some “floating” neurons may be present, they could well represent entrapped neurons. A well defined “specific glioneuronal element” that is diagnostic of DNT is not seen. Neuronal satellitosis is evident, and linear profiles of cells are also observed in the vicinity of the tumour. The appearance is consistent either with reactive oligodendrogliosis, or peripheral extension of the tumour. As previously mentioned, this low-grade tumour is interpreted as being a 'circumscribed' glioma rather than a diffusely infiltrating glioma.
Final Diagnosis: Dysembryoplastic neuroepithelial tumour (DNET), non-specific variant
Comment: The “specific glioneuronal element” of DNET was not well defined in this low-grade neoplasm. An element resembling pilocytic astrocytoma is very prominent. The “non-specific variant” of DNET is a somewhat controversial designation that may encompass a variety of histologically diverse lesions that are characterized by the following common features: young age, superficial location, and indolent course that require no further treatment beyond initial surgery. This tumour falls within this category.