Giant suprasellar varix: an unusual cause of chiasmal compression.

A 63-year-old woman developed visual field defects consistent with lateral compression of the optic chiasm. The cause of the compression was found to be a giant venous varix formed by the dilatation of the outflow vein from a dural arteriovenous fistula located in the superior petrosal sinus. After embolization and surgical obliteration of the fistula, the patient's visual function improved markedly.