MICROSCOPIC DESCRIPTION
Paraffin sections show a variably hypercellular oligodendroglioma. Tumour cells show mild nuclear pleomorphism and are arranged in diffuse sheets. Areas with a vaguely lobular pattern are noted with lobules enclosed by thin-walled vessels. An occasional mitotic figure is identified. There is no microvascular proliferation and no necrosis is seen. Tumour is centred largely within white matter but focally extends into cortex where there is prominent perineuronal and perivascular secondary structuring. No breach of the pia-arachnoid is seen.
IMMUNOHISTOCHEMISTRY
GFAP positive in reactive astrocytes and gliofibrillary oligodendrocytes; negative in oligodendroglial cells. NogoA positive in oligodendroglial tumour cells. IDH-1 R132H positive MGMT positive (likely unmethylated) p53 negative p16 positive Topoisomerase labelling index: Approximately 3%.
DIAGNOSIS
Oligodendroglioma (WHO Grade II)