Papillary glioneuronal tumor

Ill-defined hyperdense mass within the anterior pole of the left temporal lobe associated with surrounding vasogenic edema. No midline shift or cerebral herniation. Remainder brain parenchyma is unremarkable. 

The left temporal lobe mass demonstrates a few prominent vessels within associated with a small hemorrhagic foci, has vivid rim enhancement, and shows partial diffusion restriction. Local mass effect and vasogenic edema are again demonstrated 

MICROSCOPIC DESCRIPTION: 1-3. Sections show a moderately cellular biphasic tumor composed of thin hyalinised blood vessels surrounded by small astrocytes (GFAP+), together with intervening neurocytes (Synaptophysin+) and occasional ganglion cells (NeuN+). There is focal moderate nuclear atypia and occasional mitoses. No pallisaded tumor necrosis or microvascular proliferation with multilayering of atypical cells around vessel lumena. Immunohistochemistry results show tumor cells stain: Nestin Positive (high) NogoA Positive IDH-1 R132H Negative (non-mutated) ATRX Negative (mutated) MGMT Positive (likely non-methylated) p53 Positive p16 CDKN2A Positive EMA Negative CD99 Negative Topoisomerase labeling index: Approximately 25%.

DIAGNOSIS: Brain, left temporal lesion: Papillary glioneuronal tumor (WHO I)

Comment: The histologcal and immunohistochemical features are most consistent with a papillary glioneural tumor (PGNT). A high proliferation index has been previously reported within PGNT, however close clinical follow-up is recommended. Additionally, immunohistochemical results show tumor cells with intact staining for MSH2, MSH6 and MLH1, whilst there is loss of staining for PMS2. Correlation with the known microsatellite instability related bowel lesions (Lynch Syndrome) is recommended.