Elsevier

World Neurosurgery

Volume 112, April 2018, Pages 39-45
World Neurosurgery

Literature Review
Supernumerary Abducens Nerves: A Comprehensive Review

https://doi.org/10.1016/j.wneu.2017.11.052Get rights and content

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.

Introduction

The abducens nerve has a long, tortuous intracranial path with multiple fixation points, causing it to be vulnerable to various pathologies.1, 2, 3, 4, 5, 6, 7 The nerve originates from the pontomedullary sulcus, on the ventral side of the brainstem. It travels upward and anteriorly along the clivus, in the prepontine cistern, lateral to the basilar artery.8, 9, 10 When piercing the dura mater at the petroclival region to reach the cavernous sinus, it travels through Dorello canal formed by the petroclinoid ligament (Gruber ligament) (Figure 1). Within the cavernous sinus, the nerve travels laterally over the cavernous internal carotid artery. As it reaches the orbit through the superior orbital fissure, it travels medial to the ophthalmic branch of the trigeminal nerve. As the abducens reaches the lateral rectus muscle, it splits into superior and inferior branches and enters the proximal half of the muscle.11, 12, 13 Although this pathway is the most common, several studies have shown multiple abducens nerve branches with a prevalence of 5%–28.6%.4 Considering that abducens nerve palsy is the most common extraocular nerve palsy, these anatomic variants warrant further investigation. We review available literature, postulate causes for abducens nerve variations, and discuss several unknowns as aims for future studies.

Section snippets

Materials and Methods

A systematic literature search was performed using PubMed and Google Scholar with the terms “abducens nerve,” “variation,” “duplication,” “aberrant,” and “recurrent.” Only relevant articles with human subjects, written in English, and published in peer-reviewed journals were included.

Results

The initial search yielded 76 studies. After screening, 16 studies were included in the final analysis. Of the 16 articles, 11 were cadaveric studies and 6 were case reports.

Clinical Relevance

Owing to its long, tortuous path through the cranium, the abducens nerve is vulnerable to injury and thus is the most common extraocular nerve palsy. A variety of causes can lead to abducens nerve palsy such as intracranial hypertension or hypotension, aneurysms, ligament entrapment, and surgical procedures.1, 20, 22, 23, 24, 25 Despite the complex anatomy, most cases of abducens nerve variations were found incidentally with subjects possessing normal ophthalmologic function.19, 20, 21, 22

One

Conclusions

Given its long and complex intracranial route, the abducens nerve can be vulnerable to iatrogenic injury and neurovascular interactions with its surrounding structures, resulting in abducens nerve palsy. Knowledge of anatomic variations of the abducens nerve is essential for improving procedural outcomes and patient safety.

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    Conflict of interest statement: The authors declare that the article content was composed in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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