Pilocytic astrocytoma

Case contributed by Assoc Prof Frank Gaillard



Patient Data

Age: 25 years
Gender: Male

Arising from the right side of the midbrain is a mass which is mixed solid cystic. The solid component, which has smaller cysts embedded within it and is associated with a cyst around its posterior superior aspect.

The cystic component can be seen to displace the pineal gland superiorly, which is distinct from mass, and the tectal plate which is displaced posterosuperiorly. The mass is clearly extraventricular with the third ventricle displaced towards the left. The aqueduct is obstructed with established obstructive hydrocephalus and transependymal edema.

The mass demonstrates no calcification intermediate ADC values and no evidence of hemorrhage. No abnormal flow voids. Cerebral blood volume is elevated in the enhancing component (not shown). MR spectroscopy demonstrates increased minor increased choline but is generally non-contributory (not shown).


Partially solid/cystic mass arising from the right side of the midbrain. By far the most likely diagnosis is that of a pilocytic astrocytoma/pilomyxoid astrocytoma.


Sections show a mildly cellular glioma composed of hyperchromatic nuclei set within a densely fibrillary stroma. Tumor cells demonstrate focal nuclear pleomorphism with nuclear enlargement and multinucleation. There are scattered Rosenthal fibers and eosinophilic granular bodies present. No mitoses are seen. There is no necrosis or microvascular proliferation identified.

Immunohistochemistry and genetic results:

  • GFAP: Positive
  • IDH-1 R132H: Negative (non-mutated)
  • ATRX: Positive (non-mutated)
  • p53: Positive BRAF: Negative
  • Topoisomerase labeling index: 2%.
  • BRAF-KIAA1549 translocation: No mutation detected. 

FINAL DIAGNOSIS: pilocytic astrocytoma - WHO Grade I

Case Discussion

It is important to remember that in the non-pediatric population, pilocytic astrocytomas are often supratentorial and can be both unusual in appearance and more aggressive. 

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Case information

rID: 63157
Published: 22nd Jun 2019
Last edited: 23rd Nov 2019
Inclusion in quiz mode: Included