Choristoma of the optic nerve and chiasm.

A 21-year-old patient with a biopsy-proved choristomatous malformation of the optic nerve and chiasm is presented. The patient experienced progressive unilateral vision loss and optic atrophy. A gadolinium-enhanced magnetic resonance image demonstrated chiasmal involvement that was not evident on computed tomographic scan or visual field testing. We believe this is the third reported case of a choristomatous malformation of the optic nerve and chiasm and the first report of magnetic resonance imaging findings.