Relationships of the cisternal segment of the trochlear nerve

Object. The cisternal portion of the trochlear nerve (fourth cranial nerve) can easily be injured during intracranial surgical operations. To help min imize the chance of such injury by promoting a thorough understanding of th e anatomy of this nerve and its relationships to surrounding structures, th e authors present this anatomical study. Methods. In this study, in which 12 cadaveric heads (24 sides) were used: t he authors describe exact distances between the trochlear nerve and various surrounding structures. Also described are relatively safe areas in which to manipulate or enter the tentorium, and these are referenced to external landmarks. Conclusions. This information will prove useful in planning and executing s urgical procedures in and around the free edge of the tentorium cerebelli.