Dysembryoplastic neuroepithelial tumor (DNET)
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There is a solitary T1 hypointense, T2 hyperintense lesion in the white matter of the left temporal lobe. The lesion demonstrates a central nodule of ring enhancement with no elevation of CBV or diffusion restriction. The lesion partially suppresses on FLAIR imaging and exerts minimal positive mass effect with no subfalcine, tonsillar or uncal herniation. A prominent peripheral rim of high FLAIR signal persists. MR spectroscopy demonstrates reversal of the choline to creatine ratio with elevated NAA within the left temporal lobe lesion. The remainder of the brain is unremarkable.
Conclusion: FLAIR rim sign is characteristic of a DNET although the degree of enhancement is not typical. Possibilities also include other low-grade tumors (e.g. ganglioglioma or pleomorphic xanthoastrocytoma). A higher grade tumor is also a possibility.
The patient went on to have surgery.
MICROSCOPIC DESCRIPTION: Paraffin sections show a moderately hypercellular tumor. This is composed of cells with neurocytic morphological features - small round hyperchromatic nuclei with delicate processes that are strongly immunopositive for synaptophysin. There are arranged in columns in association with small capillary vascular channels and GFAP positive glial cells forming glioneuronal elements. These enclose collections of myxomatous/mucinous material in which scattered "floatinmg" neurons are noted. These are highlighted by NeuN immunostaining. No mitotic figures or areas of necrosis are identified. No immunostaining for IDH-1 R132H is seen. Immunostaining for ATRX and p16CDKN2A is preserved. The topoisomerase labeling index is approximately 2%. The features are of dysembryoplastic neuroepithelial tumor (DNET).
FINAL DIAGNOSIS: Dysembryoplastic neuroepithelial tumor (DNET) - WHO Grade I.