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Most easily seen on FLAIR are multiple regions of high T2 signal with positive mass effect. These involve the mesial temporal lobe on the right, extending up into the splenium of the corpus callosum and medial occipital lobe as well as involving the posterior thalamus. Additional high T2 signal and thickening of the cortex is noted in the posterior aspect of the insular
cortex. On the left region of similar change involves the parietal lobe, and middle and inferior temporal gyrus. On postcontrast imaging there is possible subtle wispy enhancement in the region of the splenium corpus callosum.
MR spectroscopy is largely unremarkable. MR perfusion suggests minor elevation of cerebral blood volume (CBV) in the region of the right side of the splenium of the corpus callosum.
Scattered through the white matter are patchy regions of high T2 signal, non -specific but suggestive of chronic small vessel ischaemic change. Remainder of the brain is unremarkable in appearance.
Multiple regions of high T2 signal with mass effect scattered across more than 3 lobes does not appear convincingly different from the previous MRI, although only 6 weeks have elapsed making all but rapid growth difficult to identify. Correlation with older studies is recommended.
Appearances favours gliomatosis cerebri, especially in light of marginal elevation of the cerebral blood volume (CBV) and possible wispy enhancement.
The patient went on to have a biopsy.
MICROSCOPIC DESCRIPTION: The sections show features of a densely cellular glial tumour. Most of the tumour cells are astrocytic with elongated, angulated and pleomorphic nuclei (>90%). A second minor population of intermixed neoplastic oligodendroglial cells is also present (<10%). These cells have round nuclei and perinuclear haloes. Some tumour cells extend to involve the cerebral cortex. Scattered mitotic figures are identified (more than 5 per 10 high power fields). Endothelial cell hyperplasia is absent. No necrosis is seen. The tumour cells are p53 positive. The Ki-67 index is 10-12%. MGMT and IDH-1 immunostains are negative. The features are those of anaplastic oligoastrocytoma.
DIAGNOSIS: Anaplastic oligoastrocytoma (WHO Grade III).
As there is evidence of diffuse involvement of 3 or more lobes this is an example of gliomatosis cerebri.
Importantly, whereas gliomatosis was previously considered a distinct entity, since the 2016 update to the WHO classification of CNS tumours it is now merely thought of as a growth pattern.