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Very extensive predominantly cortical based abnormality is seen throughout the superior and middle frontal gyrus extending back to involve the precentral gyrus-the parietal lobe is spared. A second area of signal abnormality and mass effect involves the insular cortex on the right, and posterior limb of the external capsule extending into the adjacent Corona radiata. Significant mass effect persists in the frontal lobe, with complete effacement of the sulci, as shown on the prior imaging, with no resolution. No abnormal contrast enhancement shown, no diffusion restriction, with heterogeneous MRS showing metabolite depletion with low NAA, and some minor elevation of Cho. No elevation of cerebral blood volume.Other areas of white matter and cortical signal change demonstrated, in the
left cerebral hemisphere, at the parieto-occipital Junction, and in the tail of the hippocampus. While the hippocampal change was present in retrospect on the prior examination, the parieto-occipital lesions were not identified. No hydrocephalus.
Conclusion: Multifocal cortical and subcortical lesions with persistent mass effect, abnormal spectroscopy, persistent for four months excludes post seizure effect alone, cerebritis would be expected to change, and the most likely single diagnosis would be of gliomatosis cerebri.
The patient went on to have a biopsy.
All the sections show features of a moderately cellular infiltrating glial tumour. The tumour has prominent extension into the cerebral cortex as well as involving the white matter. The tumour cells form aggregates and cords. Many of the tumour cells have features of oligodendrocytes. They have enlarged round nuclei and occasional perinuclear haloes. Smaller numbers of neoplastic cells are more astrocytic with elongated and angulated nuclei. Within the cortex, there is secondary structuring including perineuronal satellitosis and perivascular aggregation. Mitoses are inconspicuous. No microvascular proliferation or necrosis is present. The tumour cells show variable staining for GFAP and Nogo-A, indicating astrocytic and oligodendroglial differentiation respectively. The topoisomerase index is about 1%. IDH-1 immunostain is negative. MGMT stains about 20% of the tumour cells. The features are those of oligoastrocytoma.
Oligoastrocytoma. Based on morphology alone, the tumour would be classified as WHO grade II. However, if the radiology suggests gliomatosis cerebri (by definition, involving at least 3 lobes), then this lesion might possibly behave as a grade III tumour.
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.