Depending on the size of the lesion and its location, other features may be present, such as hydrocephalus and focal neurological dysfunction, including personality changes. The most common presenting feature (~40% of cases) is a seizure. There is a substantially higher incidence in men of all ages and of all grades tumor (M:F ~1.5) 1,17. This is substantially younger than glioblastoma IDH wildtype tumors (median 50-60 years of age) 17. IDH-mutant adult-type astrocytomas are typically diagnosed in young adults median age of 36 years for grades 2 and 3 (combined), and 38 years for grade 4) 17. Although gemistocytic astrocytoma are also no longer recognized as distinct entities, gemistocytic tissue pattern remains a histological feature 19. The terms fibrillary astrocytoma and protoplasmic astrocytomas are no longer recognized as separate entities 13.
Importantly, the diagnosis of astrocytoma, IDH mutant is an adult-type diagnosis, distinct from a variety of other pediatric-type diffuse astrocytomas (see astrocytic tumors).
Glioblastoma is now considered a separate entity and distinct and must be IDH-wildtype, and is therefore discussed separately. These IDH-mutant astrocytomas are now graded 2, 3 or 4 based on histological and molecular features, but importantly a grade 4 tumor is no longer a glioblastoma, but rather just an astrocytoma, IDH mutant WHO CNS grade 4 16. What would previously in most instances have been known as a diffuse astrocytoma or anaplastic astrocytoma or secondary glioblastoma now all come under the one diagnosis, based on the presence of IDH mutation and the demonstrated absence of 1p19q co-deletion, which if present would make the diagnosis of an oligodendroglioma 16.
The 5th edition (2021) update to the WHO classification of CNS tumors has substantially changed the classification of astrocytic tumors, building upon the prior (2016) edition that started to define tumors based on molecular characteristics 19.
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