pilocytic astrocytoma

Introduction

low grade circumscribed astrocytoma.

Epidemiology

• mainly children & young adults,
• peak incidence around 10 years of age.

Pathology

• typically located in midline structures (optic nerve, third ventricle, thalamus, median temporal lobe, brain stem & cerebellum).
• can occur anywhere in neuraxis
• less frequent but not uncommon in spinal cord
• more circumscribed than diffuse astrocytomas, expands slowly into surrounding brain.

Microscopic pathology

• variable appearance
• bipolar fusiform/piloid cells with dense fibrillation
• compact parallel bundles of cells
• biphasic pattern: 1) pilocytic areas, 2) microcystic areas with protoplasmic poorly fibrillated cells
• sometimes cells separated by mucin
• oligodendroglioma-like cells
• alignment of cells in pallisading pattern
• Rosenthal fibers
• eosinophilic granular bodies (intracytoplasmic protein droplets) alpha-1-antichymotrypsin & alpha-1-antitrypsin immunoreactive
• hyperchromatic bizarre nuclei may be present
• endothelial proliferation not uncommon
• local invasion of subarachnoid space frequent
• may have leptomeningeal involvement
• regressive changes:
  • hyalinized telangiectatic blood vessels, calcification, necrosis, lymphocytic infiltrates,

Genetics

• association with NF1 gene mutations

Radiology

MRI: well circumscribed, contrast enhancing cyst formation common

Management

Prognosis:

• corresponds to WHO grade I
• rarely progresses to malignant
• see pilomyxoid astrocytoma

More general terms

• astrocytoma (astrocytic neoplasm)

Additional terms

• pilomyxoid astrocytoma