MICROSCOPIC DESCRIPTION: 1-3. Sections show a moderately cellular biphasic tumour 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 tumour necrosis or microvascular proliferation with multilayering of atypical cells around vessel lumena. Immunohistochemistry results show tumour 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 labelling index: Approximately 25%.
DIAGNOSIS: Brain, left temporal lesion: Papillary glioneuronal tumour (WHO I)
Comment: The histologcal and immunohistochemical features are most consistent with a papillary glioneural tumour (PGNT). A high proliferation index has been previously reported within PGNT, however close clinical follow-up is recommended. Additionally, immunohistochemical results show tumour 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.