Optic chiasm distortions caused by craniopharyngiomas: clinical and magnetic resonance imaging correlation and influence on visual outcome.

OBJECTIVE

To evaluate the anatomic distortions of the optic chiasm caused by craniopharyngiomas (CPs) and their influence on preoperative and postoperative visual status.

METHODS

We conducted a retrospective investigation of 150 CPs including preoperative and postoperative magnetic resonance imaging (MRI) studies and the preoperative visual status and visual outcome after surgery. Morphologic distortions of the optic chiasm were analyzed on midsagittal MRI and correlated with preoperative vision, visual outcome, and features and topography of the CP.

RESULTS

Vision loss before operation was present in 68.7% of the patients. The type of chiasm distortion caused by the CP was the major predictive factor of preoperative visual impairment (P < 0.001). There were 6 patterns of chiasm distortion identified: nondistorted or normal (11.3%), compressed downward (18%), compressed forward (23.3%), stretched forward (18%), stretched upward (16.7%), and stretched backward (4.7%). Reduced vision was present in >80% of compressed forward and stretched chiasms. Overall, the mechanical stretching deformation of the chiasm caused a more severe visual deficit than its compression. Postoperative chiasm morphology was the major predictive factor for visual outcome (P < 0.001). There were 6 different chiasm morphologies identified after surgery: normal (52.7%), thinned (9.4%), thickened (16.7%), displaced forward (6%), displaced upward (4%), and displaced backward (2.7%). Thinned and displaced upward chiasms were associated with the highest rate of no visual improvement. A multivariate model including preoperative and postoperative chiasm distortions predicted the visual outcome in 91.3% of patients.

CONCLUSIONS

The type of chiasm distortion represents a valuable neuroradiologic finding to ascertain the preoperative and postoperative visual status.