Diffuse astrocytoma NOS ("protoplasmic")
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A large right temporal lobe mass is present without convincing enhancement. The central portions are of very high T2 signal and attenuate on FLAIR in an ill defined fashion (not cystic).
MR specroscopy demonstrates elevation of Choline and Myo-inositol.
The patient went on to have a craniotomy and excision.
MICROSCOPIC DESCRIPTION: The sections show a moderately cellular glial tumour with a proliferation of mainly protoplasmic astrocytes with some intermixed fibrillary astrocytes. The protoplasmic astrocytes have enlarged round nuclei and short GFAP+ cytoplasmic processes in a background of prominent microcystic change. The fibrillary astrocytes appear more elongated and angulated. The tumour extends to involve the cerebral cortex. Sparse mitoses are seen (0-1 per 10 high power fields). There is no endothelial cell hyperplasia or necrosis. The overall features are those of diffuse astrocytoma (predominantly protoplasmic type). The Ki-67 index is about 3-4%. p53 is diffusely positive.
DIAGNOSIS: Diffuse astrocytoma of predominantly protoplasmic type (WHO grade II).
This case illustrates very typical appearances of protoplasmic astrocytomas, a somewhat less common variant of diffuse low grade gliomas.
Until recently, protoplasmic astrocytomas were classified as a subtype low-grade astrocytoma, however, in the latest (2016) update to WHO classification of CNS tumours, protoplasmic astrocytomas no longer exists as a distinct entity.