Anaplastic 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) through anaplastic astrocytomas (WHO Grade III) to Glioblastoma (WHO Grade IV). WHO Grade I is reserved for Pilocytic astrocytomas.燗naplastic astrocytomas (WHO Grade III; shown in this image) exhibit greater degree of cellularity, nuclear pleomorphism, and mitotic activity as compared to low-grade astrocytomas. However, necrosis and endothelial proliferation - the two hallmarks of Glioblastoma (WHO Grade IV) - are absent.