CNS tumor
Other astrocytic tumors
Pilomyxoid astrocytoma


Topic Completed: 16 August 2019

Revised: 16 August 2019

Copyright: 2019, PathologyOutlines.com, Inc.

PubMed Search: Pilomyxoid astrocytoma[TI]

Eman Abdelzaher, M.D., Ph.D.
Page views in 2019 to date: 599
Cite this page: Abdelzaher E. Pilomyxoid astrocytoma. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/cnstumorpilomyxoidastro.html. Accessed November 20th, 2019.
Definition / general
Essential features
  • A variant of pilocytic astrocytoma with distinct histologic and clinical features
  • Predominantly affects infants and young children
  • Preferentially located in the hypothalamic / chiasmatic region
  • Histologically characterized by small monomorphous bipolar cells, a myxoid background and perivascular arrangement
  • Generally has more aggressive behavior than pilocytic astrocytoma due to local recurrence and cerebrospinal fluid dissemination
Terminology
  • Pilomyxoid astrocytoma (PMA)
ICD coding
Epidemiology
Sites
Pathophysiology
Etiology
Diagrams / tables

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BRAF testing in pediatric low grade gliomas

Histologic features

Clinical features
Diagnosis
  • MRI with contrast
  • Definitive diagnosis requires tissue biopsy
Radiology description
  • MRI findings (Neurol Res 2008;30:945, MedGenMed 2004;6:42):
    • Well circumscribed
    • The majority (84.6%) are solid
    • T1: isointense or hypointense signal
    • T2 / FLAIR: hyperintense signal
    • No diffusion restriction
    • Homogeneous or heterogeneous enhancement pattern
    • No peritumoral edema
    • Craniospinal imaging is advisable to detect dissemination
Radiology images

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Chiasmatic / hypothalamic pilomyxoid astrocytoma in a 3 month old infant:
DWI: no sign of restricted diffusion
T2w: homogeneous hyperintense signal
T1w: hypointense signal
T1w+ contrast: solid mass with marked enhancement

Prognostic factors
Case reports
Treatment
Gross description
Gross images

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Coronal section through hypothalamus

Frozen section description
Frozen section images

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Perivascular bipolar cells in a mucoid background

Microscopic (histologic) description
Microscopic (histologic) images

Contributed by Eman Abdelzaher, M.D., Ph.D.

Angiocentric pattern

Monomorphous cells in a myxoid background

Cytology description
Positive stains
Negative stains
Electron microscopy description
  • Bipolar tumor cells with elongated thin processes extending to rest upon the basal lamina of blood vessels
  • Abundant intermediate (glial) filaments can be seen in some cells
  • Apical surfaces may show microvilli, blebs and occasional cilia
  • Vesicles and coated pits, as well as dense core granules and synaptoid complexes may be seen (Adesina: Atlas of Pediatric Brain Tumors, 2010)
Electron microscopy images

Images hosted on other servers:

A. Bipolar, thin 
processes extending to
basal lamina of 
vessels (corresponding to
perivascular pseudorosettes by histology)
B. Dense core granules

Molecular / cytogenetics description
Molecular / cytogenetics images

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KIAA1549-BRAF fusion

Sample pathology report
  • Brain, suprasellar region, biopsy:
    • Pilomyxoid astrocytoma
    • Ancillary tests:
      • Strong positive GFAP staining
      • Focally positive for synaptophysin
      • Ki67 proliferation index: 3%
Differential diagnosis
Board review question #1
A 10 month old boy presents with a solid enhancing hypothalamic mass on MRI. Biopsy shows a highly myxoid tumor with perivascular arrangement of monomorphous cells. What is the most likely genetic alteration in this tumor?



  1. BRAF duplication / fusion
  2. H3F3A K27M mutation
  3. IDH1 and IDH2 mutations
  4. SMARCB1 / INI1 mutations
Board review answer #1
A. BRAF duplication / fusion. The histology shows pilomyxoid astrocytoma. BRAF duplication / fusion is a frequent event in this tumor. IDH1 / 2 mutations are frequent in diffusely infiltrating gliomas. SMARCB1 / INI1 mutations are the hallmark of atypical teratoid / rhabdoid tumor. H3F3A K27M mutation is associated with diffuse midline gliomas, H3 K27M mutant.

Reference: Pilomyxoid astrocytoma

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Board review question #2
A 13 month old infant presented with failure to thrive. MRI showed a suprasellar enhancing mass. Intraoperative frozen section showed monomorphous bipolar tumor cells in an abundant myxoid background. Which of the following statements describes this tumor?

  1. Has a favorable prognosis with no reported risk of recurrence
  2. Preferentially located in the cerebellum with rare cases involving other sites
  3. Shares common genetic alterations with pilocytic astrocytoma
  4. Tends to affect adults
Board review answer #2
C. Shares common genetic alterations with pilocytic astrocytoma. Pilomyxoid astrocytoma is considered a variant of pilocytic astrocytoma. They may be part of a single disease spectrum. They share common genetic alterations (BRAF duplication / fusion), some pilomyxoid astrocytomas mature into classic pilocytic astrocytomas over time and intermediate forms exist. Pilomyxoid astrocytomas tend to affect young children and are preferentially located in the hypothalamic / chiasmatic region. They are well known to exhibit a more aggressive behavior compared to pilocytic astrocytoma.

Reference: Pilomyxoid astrocytoma

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