CNS tumor
Other astrocytic tumors
Pilocytic astrocytoma
Author: Eman Abdelzaher, M.D., Ph.D.
Topic Completed: 1 March 2012
Minor changes: 19 November 2020
Copyright: 2002-2021, PathologyOutlines.com, Inc.
PubMed Search: "Pilocytic astrocytoma" CNS
See also: Pilomyxoid astrocytoma
Table of Contents
Definition / general | Epidemiology | Sites | Radiology description | Prognostic factors | Treatment | Gross description | Gross images | Microscopic (histologic) description | Positive stains | Differential diagnosisCite this page: Abdelzaher E. Pilocytic astrocytoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/cnstumorpilocyticastrocytoma.html. Accessed January 20th, 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
Epidemiology
- 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
Sites
- 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
Treatment
- 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
- GFAP (strong), PTAH, PAS (protein droplets), alpha-1-antichymotrypsin (protein droplets)
Differential diagnosis
- Diffuse astrocytoma: grades II - IV; a prognostically important distinction
- Gliosis
- Hemangioblastoma: cells appear fibrillar on frozen section
- Other cystic tumors: especially those with a cyst mural nodule architecture (pleomorphic xanthoastrocytoma and ganglioglioma)
- Piloid gliosis: hypocellular, no spongy areas, numerous Rosenthal fibers
