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AJNR Awards, New Junior Editors, and more. Read the latest AJNR updates

Case of the Week

Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada

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July 6, 2017
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Pilocytic Astrocytoma

  • Background:
    • Pilocytic astrocytoma (PA) is the most common pediatric glioma and the most common pediatric cerebellar neoplasm.
    • The tumor is most often WHO grade I, with a high 10-year survival rate of over 90%.
    • Many PAs have abnormalities in the Ras/RAF/MAPK/ERK pathway, as did this tumor, which contained an ERC2-RAF1 translocation.
  • Clinical Presentation:
    • Most (75%) PAs present in the first 2 decades, therefore making the age of this patient slightly older than usual.
    • Symptoms are reflective of tumor location. For example, tumors within the cerebellum often cause headache, hydrocephalus, truncal ataxia, gait disturbance, and appendicular dysmetria.
  • Key Diagnostic Features:
    • This particular case of pilocytic astrocytoma is atypical in that the tumor is both completely solid and nonenhancing. However, certain features are helpful in arriving at the correct diagnosis.
    • First, the cerebellar hemisphere is one of the most common locations of PAs (the other being vermis).
    • Lack of surrounding edema and well-demarcated, smooth margins are typical, reflecting the benign behavior of the tumor.
    • Characteristic hyperintensity on T2 sequence and lack of diffusion restriction due to low cellularity also provide clues to the low tumor grade.
    • Unfortunately, the calcification seen in this case is not particularly helpful; one study of 80 PAs found a calcification rate of only 14%.
  • Differential Diagnoses:
    • Due to the unusual appearance of this PA, the standard differential does not apply. Instead, the differential should include:
      • nonenhancing, solid masses of the cerebellum, such as subependymoma (rarely intraparenchymal)
      • low-grade astrocytomas, such as diffuse fibrillary astrocytoma (more often supratentorial)
      • hamartoma: seen in patients with tuberous sclerosis or neurofibromatosis 1
      • dysplastic cerebellar gangliocytoma: thickened cerebellar folia with “tigroid” pattern, plus characteristic clinical syndromes
      • ganglioglioma: more likely to have cystic change and enhancement)
  • Treatment:
    • Surgical resection is usually curative.
    • Radiation and/or chemotherapy is used for tumors of the hypothalamic region or optic chiasm and for recurrent or disseminated tumors, which are rare.

Suggested Reading

  1. Koeller KK, Rushing EJ. From the archives of the AFIP: pilocytic astrocytoma: radiologic-pathologic correlation. Radiographics​ 2004;24:1693–1708, 10.1016/S1474-4422(12)70192-8.
  2. Zhang S, Ai L, Chen XZ, et al. Radiological evaluation of infratentorial gangliogliomas in various anatomic locations of the cerebellum and brainstem. Clin Neuroradiol​ 2016 Jan 7. [Epub ahead of print],10.1007/s00062-015-0495-7.
  3. Kim Y, Lee SY, Yi KS, et al. Infratentorial and intraparenchymal subependymoma in the cerebellum: case report. Korean J Radiol 2014;15:151–55, 10.3348/kjr.2014.15.1.151 .
  4. Fernandez C, Figarella-Branger D, Girard N, et al. Pilocytic astrocytomas in children: prognostic factors – a retrospective study of 80 cases. Neurosurgery 2003;53:544–55, 10.1227/01.NEU.0000079330.01541.6E.

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American Journal of Neuroradiology: 46 (6)
American Journal of Neuroradiology
Vol. 46, Issue 6
1 Jun 2025
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