Dysembryoplastic neuroepithelial tumor (DNET) - cerebellum
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High T2 signal lesion on the right side of the vermis has central incomplete FLAIR suppression. No contrast enhancement. No calcification or evidence of a blood product. No abnormal flow voids, although a branch of the PICA is closely related to the lesion coursing anterior and inferior. The minimal localized mass effect, with no effacement of the fourth ventricle and no hydrocephalus. Some isolated lesion. MR spectroscopy and perfusion are unremarkable, with no concerning features. All dural venous sinuses are patent, with dominant outflow along the right transverse and sigmoid sinus. A prominent vein drains in the right cerebellar hemisphere, and courses immediately to the right of the falx cerebelli.
Right-sided vermis lesion, unaltered in appearance, there is no specific features. Given the absence of any change of 3 months a low-grade tumor is favored.
The patient went on to have surgery.
MICROSCOPIC DESCRIPTION: The sections show a moderately cellular tumor. It forms elongated trabeculae-like structures. These are lined by cells with round to slightly ovoid nuclei and small nucleoli. No perinuclear haloes are seen. There is myxoid material in the background. Occasional mature 'floating' neurons are seen within the lesion. Immature neurocytic cells are not identified. No mitoses are noted. There is no microvascular proliferation or necrosis.
The lesional cells are GFAP, Nogo-A and ATRX positive, indicating glial in differentiation. The topoisomerase index is 1%. Synaptophysin stains background neuropil. NeuN and B-tubulin are negative in these cells. IDH-1 and BRAF are also negative.
FINAL DIAGNOSIS: Dysembryoplastic neuroepithelial tumor (WHO Grade I).