[Optochiasmatic diastasis in tumors with suprasellar extension and duplication of the chiasma].

The opto chiasmatic diastasis whose extreme form is a duplication of the chiasma, corresponds to a longitudinal cleavage, using the well known fasciculation of the optic fibres. It has been noticed four times in the sellar and para sellar expanding processes (two adenomas, one craniopharyngioma and one metastasis). Generally, this lesion of the chiasma goes with big tumors (grade II); it has been detected four times in frontal approaches (15%) while the rhinoseptal approach represents 85% of our cases. The diastasis of the optic fibers with tendency to form double chiasma, instead of being an exception, happens in 4% of sellars tumors. It is perfectly identified by the frontal surgical approach, but is really hard or impossible to be recognized by the rhinoseptal surgical way. The mechanisms and the prognosis of this lesion are discussed.