Astrocytic Tumors

Astrocytoma is the general term applied to a diversity of glial tumors spanning WHO Grades I–IV showing cellular features of astrocytes. The subtypes are classified according to their similarity to certain nonneoplastic astrocytes, most commonly fibrillary, occasionally gemistocytic, and rarely protoplasmic. It is essential to recognize the similarities and differences, particularly in nuclear size and morphology between nonneoplastic cells and their neoplastic counterparts.

As with almost all gliomas, a fibrillary background is highly characteristic of astrocytomas, particularly conspicuous in cytological smear preparations as well as in histological sections. When a fibrillary background is absent, an alternative diagnosis should be seriously considered, particularly of lymphoma ormetastatic tumor.

The accurate grading of astrocytomas, as in all glial neoplasia, is of paramount importance in assigning the appropriate therapy and prognosis. Grading based strictly upon histological features has been somewhat augmented by molecular and genetic markers (Louis and International Agency for Research on Cancer, 2007). WHO Grade I astrocytomas comprise a very special group within gliomas since they are associated with a distinctly better prognosis over WHO Grade II–IV astrocytomas, and the pilocytic astrocytoma exemplifies this group best. Higher grades are assigned based upon the additive criteria of

• nuclear atypia (WHO Grade II)

• conspicuous mitotic activity (WHO Grade III), and

• vascular proliferation and/or necrosis (WHO Grade IV).