CNS tumor

Other astrocytic tumors

Pilocytic astrocytoma



Minor changes: 9 September 2021

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PubMed Search: Pilocytic astrocytoma[TI] CNS tumor "free full text"[sb]

See Also: Pilomyxoid astrocytoma

Rebecca Yoda, M.D.
P.J. Cimino, M.D., Ph.D.
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Cite this page: Yoda R, Cimino PJ. Pilocytic astrocytoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/cnstumorpilocyticastrocytoma.html. Accessed September 21st, 2021.
Definition / general
  • Circumscribed, well differentiated astrocytic neoplasm with piloid (hair-like) processes, most commonly occurring in children and young adults, WHO grade 1 (Acta Neuropathol 2016;131:803)
Essential features
Terminology
  • Pilocytic astrocytoma
  • Juvenile pilocytic astrocytoma (not recommended)
  • Spongioblastoma (not recommended)
  • Pilomyxoid astrocytoma (subtype)
  • Optic nerve glioma
ICD coding
  • ICD-O: 9421/1 - pilocytic astrocytoma
  • ICD-11: 2A00.0Y - other specified gliomas of brain
  • ICD-11: XH29Q5 - pilomyxoid astrocytoma
Epidemiology
Sites
  • Found throughout neuraxis
  • Most common sites: cerebellum (42%), supratentorial (36%), optic pathway / hypothalamus (9%), brainstem (9%), spinal cord (2%) (J Neurosurg 2003;98:1170)
  • Infratentorial location most common in childhood (J Neurooncol 2017;131:163)
Pathophysiology
  • Mutation in MAPK pathway component → pathway activation → transcription factor activation → increased cell growth and proliferation
  • Biallelic inactivation of NF1 in the setting of neurofibromatosis type 1 (Genome Res 2013;23:431)
Etiology
  • Most cases are sporadic
  • Germline mutations in MAPK pathway genes, including FGFR1, NF1, PTPN11 and RAF1
Diagrams / tables

Images hosted on other servers:

MAPK pathway mutations

Clinical features
  • Neurological deficits depending on tumor location
  • Nonlocalizing signs
    • Macrocephaly
    • Headache
    • Endocrinopathy
    • Increased intracranial pressure
  • Optic pathway tumors in 15% of patients with neurofibromatosis type 1 (Ophthalmology 1984;91:929)
Diagnosis
  • Diagnosis may be made on histologic features alone (Acta Neuropathol 2015;129:775)
  • When microscopic findings are limited / ambiguous, molecular testing may be necessary to assess for gene fusions and other alterations
Radiology description
  • Well demarcated enhancing mass (Insights Imaging 2014;5:387)
  • Cystic mass with enhancing mural nodule (~66% of cases), solid or heterogeneous mixed solid - cystic
  • Fusiform mass in optic pathway
Radiology images

Contributed by P.J. Cimino, M.D., Ph.D.
T1 postcontrast MRI

T1 postcontrast MRI

Prognostic factors
Case reports
Treatment
Clinical images

Images hosted on other servers:

Intraoperative surgical image

Exophthalmos - optic nerve glioma

Orbital pilocytic astrocytoma

Gross description
  • Usually well circumscribed (Acta Neuropathol 2015;129:775)
  • Commonly cystic
  • May have myxoid or mucoid appearance
  • May contain calcifications or hemosiderin staining
Gross images

Images hosted on other servers:

Intraocular pilocytic astrocytoma

Cerebellar tumor

Optic nerve tumor

Frozen section images

Contributed by P.J. Cimino, M.D., Ph.D.
Atypical piloid glial cells

Atypical piloid glial cells

Microscopic (histologic) description
  • Growth pattern
    • Predominantly solid / circumscribed; often limited peripheral infiltration
    • Frequent extension into subarachnoid space
  • Biphasic appearance
    • Compact fibrillar portions: elongated nuclei, bipolar piloid processes, Rosenthal fibers
    • Loose microcystic portions: round to oval nuclei, cobweb-like processes, eosinophilic granular bodies
  • Occasional "pennies on a plate" multinucleated cells
  • Oligodendroglioma-like areas may be present
  • Glomeruloid vessels
  • Regressive / degenerative changes
    • Degenerative atypia
    • Vascular hyalinization
    • Infarct-like necrosis
    • Calcification
    • Perivascular lymphocytes
  • Anaplasia in a minority of cases
  • Pilomyxoid astrocytoma subtype
    • Variant with angiocentric arrangement of monophasic bipolar tumor cells in a myxoid background
Microscopic (histologic) images

Contributed by P.J. Cimino, M.D., Ph.D.
Biphasic appearance

Biphasic appearance

Compact fibrillary area

Compact fibrillary area

Cystic area

Cystic area

Rosenthal fibers

Rosenthal fibers

Eosinophilic granular bodies

Eosinophilic granular bodies

Microvascular proliferation

Microvascular proliferation


Multinucleated cells

Multinucleated cells

Hyalinized vessels

Hyalinized vessels

Extensive regressive features

Extensive regressive features

Oligodendroglial-like cytomorphology

Oligodendroglial-like
cytomorphology

Mitosis

Mitosis

GFAP piloid processes

GFAP piloid processes


Rosenthal fiber - GFAP

Rosenthal fiber - GFAP

ATRX retained nuclear immunoreactivity

ATRX retained nuclear immunoreactivity

Increased Ki67 with anaplasia

Increased Ki67 with anaplasia

Masson trichrome - EGBs

Masson trichrome - EGBs

Virtual slides

Images hosted on other servers:
Pilocytic astrocytoma (grade I)

Pilocytic astrocytoma (grade I)

Cytology description
  • Smear preparation (alcohol fixed, H&E stained) (Cancer Cytopathol 2015;123:331)
    • Mildly atypical glial cells with long piloid processes
    • Ovoid nuclei with delicate chromatin
    • Rosenthal fibers
    • Eosinophilic granular bodies
Cytology images

Contributed by P.J. Cimino, M.D., Ph.D.
Smear (squash) preparation

Smear (squash) preparation

Negative stains
Electron microscopy description
  • Rosenthal fibers: amorphous, electron dense elements surrounded by intermediate filaments within astrocytic processes (J Pathol Transl Med 2015;49:427)
  • Eosinophilic granular bodies: round body, electron dense homogeneous material
Electron microscopy images

Images hosted on other servers:

Eosinophilic granular bodies

Molecular / cytogenetics description
  • Activating alterations in components of MAPK pathway (Nat Genet 2013;45:927, Nat Genet 2013;45:602)
    • > 70% KIAA1549-BRAF fusion due to 7q34 tandem duplication
      • ~90% cerebellar cases
      • ~50% supratentorial cases
    • ~5% other BRAF fusion
    • ~5% BRAF V600E
    • ~8% NF1 loss
    • < 5% FGFR1 mutation
    • < 5% FGFR1 fusions / internal tandem duplication
    • ~2% NTRK fusions
    • PTPN1 mutation (rare)
    • KRAS mutation (rare)
    • RAF1 fusions (rare)
  • Chromosomal polysomies (5, 6, 7, 11, 15) detected by comparative genomic hybridization (CGH) (J Neuropathol Exp Neurol 2006;65:1049, Br J Cancer 2000;82:1218)
  • Infratentorial / supratentorial tumors show distinct gene expression and DNA methylation signatures (Acta Neuropathol 2013;126:291)
  • H3 K27M mutation (rare) (Brain Pathol 2019;29:126)
  • Negative for IDH1 / IDH2 exon 4 mutations
  • Usually negative for TP53 mutations
Molecular / cytogenetics images

Images hosted on other servers:

KIAA1549-BRAF fusion by FISH

Copy number variation plot

NTRK2 fusion by next generation sequencing

NF1 biallelic inactivation

Pilocytic astrocytoma methylation classifier

Videos

Pilocytic astrocytoma

Rosenthal fibers in pilocytic astrocytoma

Sample pathology report
  • Brain, cerebellum, biopsy:
    • Pilocytic astrocytoma, WHO grade 1 (see comment)
    • Comment: Positive for KIAA1549-BRAF fusion.
Differential diagnosis
Board review style question #1

The above tumor is from the cerebellum of a child. What is the most common underlying genetic alteration in this entity?

  1. TP53 mutation
  2. IDH1 R132H
  3. BRAF V600E mutation
  4. BRAF fusion involving KIAA1549
  5. NF1 loss
Board review style answer #1
D. BRAF fusion involving KIAA1549. TP53 mutations (answer A) are uncommon in pilocytic astrocytoma. IDH1 R132H (answer B) is the most common mutation in IDH mutant astrocytomas and oligodendrogliomas but should be negative in pilocytic astrocytomas. BRAF V600E mutation (answer C) and NF1 loss (answer E) occur in pilocytic astrocytomas at lower frequencies.

Comment Here

Reference: Pilocytic astrocytoma
Board review style question #2
Which of the following is true of pilocytic astrocytomas?

  1. Show diffuse p53 immunoreactivity
  2. Most frequently occur in adults
  3. Demonstrate reticulin rich foci
  4. Associated with neurofibromatosis 2
  5. Potentially curable with resection
Board review style answer #2
E. Potentially curable with resection. Pilocytic astrocytomas should not show significant p53 immunopositivity (answer A) and they usually occur in children (answer B). Reticulin rich foci are a more typical feature of pleomorphic xanthoastrocytoma or gliosarcoma (answer C). In addition, pilocytic astrocytomas are associated with NF1 (answer D).

Comment Here

Reference: Pilocytic astrocytoma
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