Oligodendroglioma NOS

Cortical and subcortical T2 hyperintensity and expansion is again identified in the left paramedian frontal lobe, with no enhancement but containing a small region of diffusion restriction. Spectroscopy trace in the left frontal lesion demonstrates increased choline and reduced NAA but no lactate peak. No convincing CBV increase.

A smaller focal region of cortical and subcortical T2 hyperintensity in the paramedian right parietal lobe demonstrates more pronounced diffusion restriction. There is no pathological contrast enhancement.

6 mm focus of T2 hyperintensity in right temporoparietal white matter is non-specific. No further abnormality identified. No hydrocephalus.

Conclusion:

Appearance is most consistent multifocal low-grade glioma.

MICROSCOPIC DESCRIPTION

Paraffin sections show a variably hypercellular oligodendroglioma. Tumor 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. Tumor is centered 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 tumor cells. IDH-1 R132H positive MGMT positive (likely unmethylated) p53 negative p16 positive Topoisomerase labeling index: Approximately 3%.

DIAGNOSIS

Oligodendroglioma (WHO Grade II)