Supernumerary Abducens Nerves: A Comprehensive Review

Background: Branching and/or replication of the abducens nerve is not an uncommon occurrence. Although numerous variations have been documented, the rarest forms are duplicated or triplicated nerves, where multiple nerve roots originate from the brainstem, travel intracranially, and attach to the lateral rectus as separate entities. Methods: We conducted a systematic literature search on the topic of supernumerary abducens nerve, using PubMed and Google Scholar. Results: After screening, 16 studies were included: 11 cadaveric studies and 6 case reports. Conclusions: In this paper, we review the literature on variations found, discuss current hypotheses and clinical relevance, and propose future studies. Neurosurgeons should be aware of such nerve variants when viewing imaging or operating in the regions traversed by the abducens nerve.