Presentation
Ataxia.
Patient Data
Rounded FLAIR hyperintense vermian mass with central faint enhancement and central susceptibility induced signal loss suggestive of small hemorrhage within the lesion. No associated CBV elevation. The mass demonstrates facilitated diffusion compared to the adjacent brain. Spectroscopy trace is non-contributory. The mass mildly partially effaces the fourth ventricle without evidence of hydrocephalus.
Conclusion
The vermian mass has a differential that includes pilocytic astrocytoma/pilomyxoid astrocytoma although usually they have more florid enhancement. Medulloblastoma in this age group is more frequent in the cerebellar hemispheres and would be expected to have lower ADC values. A DNET can have this appearance, although this appears somewhat larger and more solid than is usual.
Case Discussion
The patient went on to have a resection.
Histology
Sections show the cerebellum infiltrated by a glial tumor of only moderate cellularity. The tumor cells have elongated nuclei and fine processes. Rosenthal fibers and eosinophilic granular bodies are widespread. In some areas, the stroma is much looser and somewhat microcystic. There are no mitoses, necrosis or microvascular proliferation.
Immunohistochemistry
GFAP: positive
OLIG2: positive
IDH1 R132H: negative (not mutated)
ATRX: positive (not mutated)
p53: mosaic (wildtype)
p16: positive
BRAF V600E: negative
S100: positive
H3K27M: negative
Ki67: <1%
Final diagnosis
Pilocytic astrocytoma (CNS WHO grade 1).
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