Dysembryoplastic neuroepithelial tumor (DNET)
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A lesion on the inferior surface of the left frontal lobe is characterized by high T2 signal in the subcortical white matter with minor intrinsic high T1 signal and no discernable contrast enhancement.
The patient went on to have a resection.
Sections show brain tissue, including cerebral cortex and white matter, with areas of a relatively localized and superficial low-grade glial tumor. The tumor cells are fibrillar, and in areas display a bipolar appearance. There is a propensity for perivascular localization with nuclear-free zones between vessels. Mitotic activity is not increased. Vascular neurogenesis is not seen. Necrosis is not evident. Some areas display a loose hypocellular and cystic background. Small microcystic areas are also focally evident. Individual tumor cells are round to oval-shaped, and elongated, depending on the orientation. Some granular bodies are seen. Floating neurons are not well-defined, although entrapped neurons are observed within several parts of the tumor. In some areas, the pattern of architectural arrangement of neurons is irregular, consistent with focal cortical dysplasia. A ganglion cell component of a ganglioglioma is not definitively excluded.
FINAL DIAGNOSIS: dysembryoplastic neuroepithelial tumor (DNET).