Pathology of Cerebellar Astrocytomas in Children

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: