Pathophysiology
- W.H.O. grade used to describe: The W.H.O. 4-point grading system is used to describe these tumors, with grade 1 representing the most benign pilocytic astrocytomas; grade 2, the fibrillary astrocytomas; and grades 3 and 4, the malignant astrocytomas.
- Site of origin: There does not seem to be a preferred location of origin for these tumors.
- Gross appearance: These tumors tend to have a margin that bends over a short distance with the surrounding normal cerebellar parenchyma.
- Infiltrative: These tumors tend to infiltrate to a varying degree based on the tumor grade. Low grades do not infiltrate to the degree that higher grades do.
Molecular/Genetic Pathology
Histopathology
Features of cerebellar astrocytomas typically include the following (8):
- Biphasic pattern with varying proportions of Rosenthal fibers and multipolar cells with microcysts and granular bodies
Typical biphasic pattern of compact areas and hypocellular areas with microcysts:
Squash preparation of a pilocytic astrocytoma showing Rosenthal fibers and piloid cells:
- Low MIB-1: Low to moderate cellularity with low proliferative (MIB-1) index
Low MIB-1 proliferative index in a pilocytic astrocytoma:
- GFAP positivity
GFAP positivity in cerebellar pilocytic astrocytoma:
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