Fig. 3

Histopathology of adult pilocytic astrocytoma. Pilocytic astrocytoma with anaplastic features. The tumor consists of multiple well-circumscribed nodules, some with dense calcification. a Some nodules consist of tightly packed spindle cells with hyperchromatic nuclei (magnification 2× hematoxylin and eosin [H&E]). b Mitoses are readily identified in these areas (magnification 10× H&E). Note the perivascular pseudorosettes. Other nodules exhibit conventional pilocytic astrocytoma morphology with (c) the classic biphasic pattern (magnification 20× H&E). The tumor cells are strongly immunoreactive for S100, GFAP, and (d) Olig2 (magnification 20× H&E)