Diffuse astrocytoma NOS ("protoplasmic")
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A large mass located in the anterior temporal lobe, insular cortex and extending into the inferior frontal lobe is demonstrated. Parts of the mass, which is mostly high T2 signal, attenuate on FLAIR. A single region of contrast enhancement is present. At the margins of the 'cystic' area is a rim of relative restricted diffusion.
The patient went on to have a craniotomy and resection of the tumour.
Paraffin sections show a moderately hypercellular glioma composed
predominantly of protoplasmic astrocytes with lesser numbers of fibrillary and occasional gemistocytic astrocytes. Protoplasmic cells have mildly pleomorphic round and oval hyperchromatic nuclei and delicate processes. No mitotic figures are identified and there is no vascular endothelial cell hyperplasia and no necrosis. The Ki-67/MIB-1 proliferation index is approximately 7%. Prominent microcyst formation is seen. Tumour is seen to infiltrate white matter but is relatively well demarcated from the cortex.
FINAL DIAGNOSIS: Diffuse astrocytoma of protoplasmic type (WHO Grade II)
Note: 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, but rather are considered as a pattern of certain gliomas, requiring IDH +/- 1p19q status for classification.