pilocytic astrocytoma

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

References

WHO Classification Tumours of the Nervous System. Kleihues & Cavenee eds. IARC Press 2000