CNS tumor
Other astrocytic tumors
Pilocytic astrocytoma

Topic Completed: 1 March 2012

Minor changes: 23 April 2021

Copyright: 2002-2021,, Inc.

PubMed Search: "Pilocytic astrocytoma" CNS

See also: Pilomyxoid astrocytoma

Eman Abdelzaher, M.D., Ph.D.
Page views in 2020: 21,553
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Cite this page: Abdelzaher E. Pilocytic astrocytoma. website. Accessed May 6th, 2021.
Definition / general
  • Pilocytic means "hair-like," due to long, bipolar processes
  • Most common CNS neoplasm of childhood
  • Better prognosis than diffuse types, particularly if resectable (such as cerebellar tumors)
  • WHO grade I
  • Most common CNS neoplasm of childhood; incidence of 1/100K
  • Most commonly arises during the first two decades of life (peak age 8 - 13 years)
  • May arise in adults (rare after 50 years, Br J Neurosurg 2004;18:613)
  • No gender predilection
  • Usually involves midline structures in posterior fossa including cerebellum; also third ventricle, thalamus, hypothalamus, neurohypophysis
  • Also optic nerve (optic nerve glioma), optic chiasm / hypothalamus, thalamus and basal ganglia, cerebral hemispheres, cerebellum (cerebellar astrocytoma), brain stem (dorsal exophytic brain stem glioma), spinal cord, may occupy the ventricles
  • May be multicentric
Radiology description
  • Pilocytic astrocytomas are well circumscribed and contrast enhancing, often cystic masses
  • Some assume cyst mural nodule architecture (Radiographics 2004;24:1693)
  • Optic tumors form a fusiform enhancing mass
  • Brain stem tumors are relatively discrete, often exophytic and variably contrast enhancing
Prognostic factors
  • 10 year survival is 100% if supratentorial and gross total resection vs. 74% if subtotal resection
  • Invasion of subarachnoid space and endothelial proliferation are NOT poor prognostic factors
  • Resection; radiation and chemotherapy for tumors of optic pathway and hypothalamic region; rarely recurs or disseminates
Gross description
  • Discrete and often cystic
  • Microcystic or macrocystic; may have mural nodule
Gross images

Images hosted on other servers:

Cerebellar tumor

Optic nerve tumor

Microscopic (histologic) description
  • Bipolar neoplastic cells with elongated hair-like processes that are arranged in parallel bundles and resemble mats of hair
  • Rosenthal fibers (tapered corkscrew shaped, brightly eosinophilic, hyaline masses), often associated with eosinophilic protein droplets (resembling foamy macrophages); may have microscopically infiltrative margin; mural nodule may be highly vascular; often calcifications
  • Rarely malignant degeneration with hypercellularity, mitotic figures and necrosis
  • Characterized by a biphasic pattern with varying proportions of piloid areas alternating with spongy areas
  • Piloid areas are formed of compacted strongly GFAP+ bipolar cells (with hair-like bipolar processes) associated with Rosenthal fibers
  • Spongy areas are loosely textured and formed of weakly GFAP+ multipolar cells (protoplasmic astrocytes) associated with microcysts and eosinophilic granular bodies (brightly eosinophilic PAS+ globular aggregates)
  • Vascular changes are common including glomeruloid vascular proliferation and vascular hyalinization
  • Degenerative changes include hyalinized blood vessels, infarct-like necrosis, degenerative nuclear atypia, calcification, hemosiderin deposits and lymphocytic infiltrate
  • Leptomeningeal extension is not a sign of malignancy
  • Some cerebellar tumors show a diffuse growth pattern
Positive stains
Differential diagnosis
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