Surgical anatomy of the cisternal segment of the trochlear nerve

In this paper the author describes the results of an anatomical study of the cisternal segment of the trochlear nerve, performed on 10 adults cadavers, The anatomical aspects of surgical interest are emphasized in relation to the cisternal course of the 4 th cranial nerve, dividing it into two segments: an initial or cerebellomesencephalic segment and a distal or tentorial segment, The long cisternal course of the trochlear nerve (35 s,d, 5 mm), its arachnoidal attachments, its thinness (0.7-1 mm thick) and its infratentorial position (in close relationship with the inner face of the tentorium cerebelli), are anatomical features that make it a potentially fragile nerve which may be inadvertently damaged during surgical manipulation to the region of the tentorial incisure, especially during transtentorial subtemporal approaches.