Pilocytic Astrocytoma Characteristics
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Questions and Answers

What is the typical appearance of a pilocytic astrocytoma on T1 imaging?

  • Hypointense
  • Variable intensity
  • Hyperintense
  • Isointense to hypointense (correct)

    • What is the average annual age-adjusted incidence rate of pilocytic astrocytoma per 100,000 population?

  • 0.5 cases
  • 1.5 cases
  • 0.1 cases
  • 0.91 cases (correct)

    • What percentage of all childhood primary brain tumours are pilocytic astrocytomas?

  • 10%
  • 15%
  • 17.6% (correct)
  • 20%

    • What is the characteristic of optic nerve tumours associated with neurofibromatosis type 1 (NF1)?

    <p>They rarely extend beyond the optic pathway</p> Signup and view all the answers

    What is the percentage of all primary brain tumours that are pilocytic astrocytomas?

    <p>5%</p> Signup and view all the answers

    What is a characteristic of the KIAA1549::BRAF fusion?

    <p>It is common in cerebellar tumours</p> Signup and view all the answers

    What is a common feature of pilocytic astrocytomas?

    <p>Low to moderate cellularity</p> Signup and view all the answers

    In which type of tumours are BRAF p.V600E mutations more common?

    <p>Supratentorial tumours</p> Signup and view all the answers

    What is a characteristic of optic nerve tumours?

    <p>They often circumferentially infiltrate the optic sheath</p> Signup and view all the answers

    What is a characteristic of the nuclei of neoplastic cells in pilocytic astrocytomas?

    <p>They are round to elongate</p> Signup and view all the answers

    What is a characteristic feature of pilocytic astrocytomas in some cases?

    <p>Rare mitotic figures</p> Signup and view all the answers

    What is a common feature of pilocytic astrocytomas?

    <p>Myxoid background with microcystic change</p> Signup and view all the answers

    What is a histological pattern seen in pilocytic astrocytomas?

    <p>Biphasic pattern</p> Signup and view all the answers

    What is a rare feature of pilocytic astrocytomas?

    <p>Palisading necrosis</p> Signup and view all the answers

    What is associated with the oligodendrocyte-like pattern in pilocytic astrocytomas?

    <p>FGFR1 alterations</p> Signup and view all the answers

    What is the primary mechanism behind the activation of NTRK fusion proteins?

    <p>Constitutive dimerization of the NTRK fusion proteins</p> Signup and view all the answers

    Which of the following genes is typically fused with BRAF in pilocytic astrocytomas?

    <p>KIAA1549</p> Signup and view all the answers

    What type of mutations are commonly seen in the FGFR1 gene in pilocytic astrocytomas?

    <p>Hotspot point mutations</p> Signup and view all the answers

    Which of the following chromosomes are reportedly involved in polysomies in pilocytic astrocytomas?

    <p>Chromosomes 5, 6, 7, 11, and 15</p> Signup and view all the answers

    What is the effect of the internal tandem duplication of the kinase domain of FGFR1?

    <p>Constitutive activation of the FGFR1 protein</p> Signup and view all the answers

    What is the most common age range for pilocytic astrocytomas with anaplasia?

    <p>Adults with a mean age of 32 years</p> Signup and view all the answers

    What is the percentage of pilocytic astrocytomas with anaplasia that show loss of nuclear ATRX expression?

    <p>57%</p> Signup and view all the answers

    What is the term used to describe the distinct methylome signature found in 81% of pilocytic astrocytomas with anaplasia?

    <p>DNA methylation class anaplastic astrocytoma with piloid features</p> Signup and view all the answers

    What is the percentage of cerebellar glioblastomas that show a similar DNA methylation profile to pilocytic astrocytomas with anaplasia?

    <p>36%</p> Signup and view all the answers

    What is the current understanding of the relationship between pilocytic astrocytomas with histological anaplasia and high-grade astrocytoma with piloid features?

    <p>They overlap partially, but their relationship remains to be elucidated</p> Signup and view all the answers

    Study Notes

    Imaging Characteristics

    • Pilocytic astrocytomas can appear as a cyst-like mass with a central non-enhancing zone or as a predominantly solid mass.
    • The cyst wall enhancement is variable, and enhancement does not necessarily indicate tumour involvement.
    • Calcification may be present.
    • Pilocytic astrocytomas are often contrast enhancing, with the solid tumour component typically being isointense to hypointense on T1 imaging and hyperintense on T2.

    Epidemiology

    • Pilocytic astrocytoma accounts for 5% of all primary brain tumours.
    • It is most common during the first two decades of life, with an average annual age-adjusted incidence rate of 0.91 cases per 100,000 population.
    • Pilocytic astrocytoma accounts for 17.6% of all childhood primary brain tumours and is the most common glioma in children.
    • The incidence rate is highest in young children and decreases with advancing age.
    • Pilocytic astrocytoma is rare in older adults.

    Genetics

    • Alterations include NF1 mutations, BRAF p.V600E mutations, BRAF fusions, BRAF insertions, KRAS mutations, FGFR1 mutations or fusions, and rare NTRK family receptor tyrosine kinase fusions.
    • NTRK genes fuse with several different 5′ partners that contain a dimerization domain, leading to constitutive dimerization of the NTRK fusion proteins and activation of the kinase.
    • FGFR1 alterations seen in pilocytic astrocytomas overlap with those seen in other paediatric low-grade glial and glioneuronal tumours.

    Macroscopic Appearance

    • Most pilocytic astrocytomas are soft, grey, and relatively discrete.
    • Intratumoural or paratumoural cyst formation, including mural tumour nodules, is common.
    • Chronic lesions may be calcified.
    • Spinal tumours may be associated with syrinx formation.
    • Optic nerve tumours often circumferentially infiltrate the optic sheath.

    Histopathology

    • Pilocytic astrocytomas have low to moderate cellularity.
    • Neoplastic cells range widely in their morphology and include varying proportions of piloid and oligodendrocyte-like cells.
    • Nuclei are round to elongate.
    • Multinucleated cells with horseshoe-shaped nuclear clusters (pennies-on-a-plate pattern) are often seen.
    • In some cases, hyperchromasia and pleomorphism are obvious, but mitotic figures are rare.

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    Learn about the characteristics of pilocytic astrocytomas, including appearance, enhancement, and calcification. Test your knowledge of these brain tumors.

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