Duplicated abducent nerve and its course: microanatomical study and surgery-related considerations

Object. The anatomy of the abducent nerve is well known; its duplication (r anging from 5 to 28.6%), however, has rarely been reported in the literatur e. The authors performed a microanatomical study in 100 cadaveric specimens (50 heads) to evaluate the prevalence of this phenomenon and to provide a clear anatomical description of the course and relationships of the nerve. The surgery-related implications of this rare anatomical variant will be hi ghlighted. Methods. The 50 human cadaveric heads (100 specimens) were embalmed in a 10 % formalin solution for 3 weeks. Fifteen of them were injected with colored neoprene latex. A duplicated abducent nerve was found in eight specimens ( 8%). In two (25%) of these eight specimens the nerve originated at the pont omedullary sulcus as two independent trunks: in one case the superior trunk was thicker than the inferior and in the other it was thinner. In the othe r six cases (75%) the nerve originated as a single trunk, splitting in two trunks into the cisternal segment: in two of them the trunks ran below the Gruber ligament, whereas in four specimens one trunk ran below and one abov e it. In all the specimens, the duplicated nerves fused again into the cave rnous sinus, just after the posterior genu of the internal carotid artery. Conclusions. Although the presence of a duplicated abducent nerve is a rare finding, preoperative magnetic resonance imaging should be performed to ru le out this possibility, thus tailoring the operation to avoid postoperativ e deficits.