Astrocytoma

Epidemiology:

Common sites:

• pilocytic astrocytomas occur along a track in the CNS:
• diffuse astrocytomas:
• supratentorial

Gross features:

Histologic features:

• pilocytic astrocytoma (low grade always):
• cells shaped like a strand of hair
• Rosenthal fibres (non-specific)
• Diffuse astrocytoma (10-15%):
• Feltwork background
• Tend to track along blood vessels, white matter tracts, ventricles (amoeboid infiltration)
• Grading: (add up each one and add 1 = grade)
• mitotic rate (should be first to occur)
• Necrosis
• Vascular proliferation:
• 3 or more layers of endothelial cells must be present
• cellularity and atypia
• Gemistocytic variant:
• Rich eosinophilic perinuclear cytoplasm
• Protoplasmic variant:
• Well-circumscribed
• GBM (grade IV diffuse astrocytoma):
• Not well-circumscribed
• No differentiation apart from astrocyte

Immunophenotype:

Marker:	Sensitivity:	Specificity:
GFAP	Often	Good
S100	100%	Poor
Vimentin
CK (particularly AE1/AE3)	Some

Molecular features:

• Loss of 19q (frequent)
• Rarely occurs with loss of 1p
• Loss of 1p (occasional)
• TP53 mutation
• 10q loss (especially common in glioblastoma)
• Nearly always in small cell astrocytoma

Other features:

• MIB-1 is usually < 1%
• 1.5 to 2.0% is unfavorable prognosis
• may contain cavernous hemangiomas
• protoplasmic variant has good prognosis
• clinical presentation: seizure à MRI

References: