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A sharply defined zone of abnormal slightly heterogeneous signal in the left parietal lobe extends to involve the medial cortex of the superior parietal lobule. Inferiorly it abuts and distorts the cingulate gyrus. Superiorly it is significantly posterior to the precentral gyrus and slightly posterior to the left post central gyrus. Posterior and laterally it extends to and distorts the left intraparietal sulcus. It extends to within 1 cm of the parieto-occipital fissure postero-medially, slightly posteriorly bowing it. It exhibits no restricted diffusion and no pathological contrast enhancement. It does show slightly elevated choline to creatine ratio, reduced NAA and a few small lactate peaks. It shows reduced relative cerebral blood volume (CBV) and relative cerebral blood flow (CBF) on perfusion studies.
The patient went on to have a resection.
Paraffin sections show a moderately hypercellular glial tumour involving cerebral cortex and white matter. Tumour cells have pleomorphic round and oval nuclei, some with perinuclear clearing. These are arranged in diffuse sheets intersected by delicate capillaries. Moderate numbers of minigemistocytes and gliofibrillary oligodendrocytes are noted. No mitotic figures are identified and there is no endothelial cell hyperplasia or necrosis.
Topoisomerase labelling index approximately 3%.
DIAGNOSIS: Oligodendroglioma (WHO Grade II)
Note: This case predates the recent (2016) revision WHO classification of CNS tumours, and as 1p19q co-deletion status is not available this tumour would now be classified as an oligodendroglioma NOS.