Presentation
Dizziness and headache.
Patient Data
Cerebellar midline patchily enhancing mass that is T2/FLAIR high signal centered on the vermis extending into the cerebellar hemispheres, more so on the right. No abnormally restricted diffusion or blooming artifact.
Superiorly, high FLAIR signal extends through the left superior cerebellar peduncle into the left periaqueductal grey matter and tectal plate with narrowing of the cerebral aqueduct. Inferiorly, high FLAIR signal extends into the left cerebellar tonsil.
Mass effect on the fourth ventricle, which is nearly effaced. Mild ventriculomegaly. Scattered high FLAIR signal foci in the centrum semiovale.
HISTOPATHOLOGY
MICROSCOPIC: Sections taken, most prominently within specimen 3, comprise a mildly to moderately cellular proliferation of cells with variably sized, bland ovoid nuclei embedded within a fibrillary background showing prominent myxoid degeneration. Focal hyalinisation of the blood vessels is also identified. No necrosis, microvascular proliferation or mitotic activity is identified. The tumor appears relatively circumscribed from the surrounding cerebellum
On immunohistochemical examination the tumor cells show positive staining for GFAP, ATRX and synaptophysin with negative staining for neurofilament, BRAF, p53 and IDH1. The tumor has a very low nuclear proliferation rate of approximately 1% on immunohistochemical examination with the proliferation marker Ki–67.
After multidisciplinary meeting review, the consensus opinion is that the lesion represents a pilocytic astrocytoma.
The characteristic piloid astrocytes with Rosenthal fibers and eosinophilic globules is not seen in the sections examined but variants of pilocytic astrocytoma are described showing predominant oligodendroglial–like cells within a myxoid background as in this case.
In addition, except for the negative staining for BRAF, the immunoprofile also is consistent with pilocytic astrocytoma.
DIAGNOSIS: Cerebellar vermis lesion: Low grade glioma showing features favoring a pilocytic astrocytoma.
Case Discussion
This case of pilocytic astrocytoma is slightly unusual occurring in the posterior fossa in an adult. The posterior fossa pilocytic astrocytomas are more common in children whereas the supratentorial brain is more common in adults.
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