Diffuse astrocytoma NOS


Features are consistent with a diffuse low-grade glioma. Only faint enhancement and absence of evidence of necrosis/hemorrhage argues against a higher grade lesion (i.e unlikely to be a GBM). 


Paraffin sections show fragments of white matter. These show a moderate increase in the numbers of astrocytic cells and prominent perineuronal and perivascular secondary structuring. Astrocytic cells show a mild degree of nuclear atypia and there is clustering of cells in many areas. No mitotic figures are seen and there is no vascular endothelial cell proliferation and no necrosis. A minority of atypical astrocytic cells show strong nuclear staining for Ki-67/MIB-1 (proliferation index approx. 5%). The features are of diffuse fibrillary astrocytoma.

FINAL DIAGNOSIS: diffuse (fibrillary) astrocytoma

Note: IDH mutation status is not provided in this case and according to the current (2016) WHO classification of CNS tumors, this tumor would, therefore, be designated as a diffuse astrocytoma NOS