Presentation
Visual loss.
Patient Data
A mass with intermediate attenuation in the suprasellar and hypothalamic region demonstrates vivid contrast enhancement. It is located between the internal carotid arteries and the basilar artery.
A suprasellar/hypothalamic mass has eroded the dorsum sellae and compressed the pituitary gland inferiorly (seen as separate from the mass).
On sagittal T2 images, the right optic nerve is elevated and can be followed towards the midline blending with the chiasm which is expanded by the mass. The left optic nerve is expanded. On coronal T2 images, the expanded optic chiasm is more easily identified with extension posteriorly into the left optic tract and into surrounding structures.
The mass has heterogeneous diffusion restriction without areas of profound restriction. Much of the mass demonstrates prominent enhancement (only dynamic post-contrast images available) and this is slower than the adjacent pituitary gland. No cystic components.
The patient went on to have a biopsy.
Histology
Sections show a moderately cellular glial tumor. The tumor is composed of relatively uniform piloid cells with oval nuclei and fine processes. In some areas, there is a slightly microcystic appearance. No mitoses or necrosis is seen. There are a few Rosenthal fibers and eosinophilic granular bodies.
Immunohistochemistry
BRAF V600E: equivocal
S100: positive
Ki6: 2-3%
p16 CDKN2A: positive (not lost)
p53: mosaic (not mutated)
ATRX: positive (not mutated)
IDH1 R132H: negative (not mutated)
OLIG2: positive
GFAP: positive
Final diagnosis
Pilocytic astrocytoma (CNS WHO grade 1)
Case Discussion
This case is a good example of how pilocytic astrocytomas, typically thought of as pediatric tumors, do occur in adults. When they do, they do not look like the typical pediatric version and are far more commonly located suptratentorially.