Diffuse astrocytoma, light micrograph. Infiltrating astrocytomas燼ccount for almost?0% of adult primary brain tumours. The usual location is燾erebral hemispheres燼nd the most commonly affected age group is?th to 6th decades. The histologic spectrum ranges from diffuse fibrillary astrocytomas (WHO Grade II; shown in this image), through anaplastic astrocytomas (WHO Grade III) to Glioblastoma (WHO Grade IV). WHO Grade I is reserved for Pilocytic astrocytomas. This image of diffuse astrocytoma (WHO Grade II) shows increased number of glial cells (cells with copious eosinophilic cytoplasm), mild nuclear pleomorphism, and a network of delicate astrocytic processes giving a fibrillary appearance to the background.