Dysembryoplastic neuroepithelial tumour (DNET)
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A lesion on the inferior surface of the left frontal lobe is characterised 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 tumour. The tumour 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 tumour 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 tumour. 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 tumour (DNET).