Intrasellar presentation of a cystic optic chiasm fibrillary astrocytoma.

The unusual radiologic presentation of an optic chiasm fibrillary astrocytoma extending through and expanding the diaphragma sellae in an 8-year-old male is described. The child presented with decreased vision in the right eye. Magnetic resonance imaging demonstrated a cystic intra- and suprasellar mass, isointense on T1WI and hyperintense on T2WI, that enhanced with contrast. There was no radiographic involvement of the pituitary or hypothalamus. The optic chiasm could not be seen. The tumor mass was believed to be a craniopharyngioma and was partially removed by a transsphenoidal approach. Frozen section was not consistent with craniopharyngioma. Histochemical stains were positive for glial fibrillary acidic protein and S100 protein and nonreactive for EMA or actin. Electron microscopy showed abundant cellular processes and cytoplasmic filaments within the cells. A diagnosis of intrasellar fibrillary astrocytoma, probably arising from the optic chiasm, was made.