Petrobasilar, petroclival, or petrosphenoidal canal of the abducens nerve
In the recently published case report entitled Anatomic variation of the abducens nerve in a single cadaver dissection: the ”petrobasilar canal” we described the exceptional course of the abducens nerve, cranial nerve VI (CNVI) . Generally, CNVI exits the pontomedullary sulcus as a single trunk, ascending in a rostral and lateral direction to reach the petrous apex. At the petrous apex the nerve pierces the visceral dura, passing over the temporal bone and below the dural sheath of the petrosphenoidal ligament in most cases, with the exception that a branch of a duplicated CNVI or the nerve itself can course above the ligament [1, 2, 3, 4].
To the best of our knowledge, our finding is difficult to place in the current literature since similar anatomic variations of CNVI have never been described. Only the reports by Wegner  and Özveren  are worth being considered carefully. More specifically, in 1920 Wegner showed that the posterior clinoid process of a gibbon extended as a broad plate posteriorly and, underneath it, the left CNVI traveled through a particular closed canal that he named “canalis nervi abducentis” . In such manner, the “petrobasilar canal” resembles the “canalis nervi abducentis” described by Wegner and comprised in the posterior clinoid process of the sphenoid bone.
Moreover, in a study on the duplication of CNVI at the petroclival region, Özveren  described one CNVI of 50 under study with an unusual course. It presented with two branches having different courses: the smaller branch traveled over the apex of the petrous bone, the larger through a bony canal named the “petrosphenoidal canal”. The “petrosphenoidal canal”, as outlined by Özveren, was formed by the junction of the petroux apex with the superolateral border of the clivus .
As a result, we reported a similar variation noted by Özveren with the difference that the nerve passing through the canal between the petrous bone and the clivus had a single branch. However, our study brings into question whether the course of CNVI under the petrous bone could have been described using the terms “petrosphenoidal” or “petroclival”.
Given the findings of our study, we did not consider the term “petrosphenoidal” since no anatomic relationship was found with the sphenoid bone, and the course of CNVI below the petrous bone was significantly below the dorsum sellae. We acknowledge that the location of the petrobasilar canal, as we have described, is at the level of the petroclival region, but the passage of the nerve through the petrobasilar suture is visible and not questionable. Thus, we think that the so-termed “petrobasilar canal”, comprised in the suture, reflects what we noticed and documented when we studied the course of CNVI.
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- 6.Wegner R (1920) Das ligamentum spheno-petrosum grtjber= abducensbriicke und homologe gebilde. Anat Anz 53:161–175Google Scholar