The Dorello Canal

Historical Development, Controversies in Microsurgical Anatomy, and Clinical Implications

Varun R. Kshettry, M.D; Joung H. Lee, M.D; Mario Ammirati M.D., M.B.A

Disclosures

Neurosurg Focus. 2013;34(3):e4 

In This Article

Clinical Implications

Initial interest in studying the anatomy of the abducent nerve arose from the occurrence of abducent palsy in clinical practice. Abducent nerve palsies have been described in trauma with or without fractures of the skull base,[4,32–34] mass effect with brainstem shift,[38] ICA aneurysms,[3,31] intracranial hypotension,[9] lumbar puncture,[23,39] shunting for hydrocephalus,[10] sphenoid sinus pathology,[8] and suppurative middle ear infections.[16] While direct injury or compression is straightforward, the etiology of indirect injuries or stretch injuries in trauma or intracranial hypotension is more peculiar. Some have hypothesized as to why the abducent nerve may be sensitive to injury in such cases. Umansky et al.[36] described 3 curves in the course of the abducent nerve. The first occurs at the dural foramen where the nerve courses laterally toward the petrous apex. The second curve extends over the petrous apex after which the nerve angles inferiorly and laterally to reach the posterior bend of the cavernous ICA. The last curve is around the posterior bend of the ICA. Of these, the most severe curve occurs over the petrous apex and would, therefore, be the point most vulnerable to blunt trauma or stretch injury. Iaconetta et al.[19] point out that there is a point of fixation at the dural porus. In cases of intracranial hypotension with brainstem sag or cervical trauma resulting in parenchymal movement within the cranium, this may be a point at which the cisternal segment of the nerve suffers stretch injury.[9] Ozveren et al.[27] point out that fixation of the nerve to the lateral wall of the cavernous ICA may also be a mechanism for abducent nerve injury in trauma. An autopsy analysis after severe head trauma demonstrated frequent contusion at this site and at the dural porus.

Knowledge of the detailed anatomy of the abducent nerve is of utmost importance to minimize risk of injury in surgical approaches to the petroclival region. The advent of endoscopic endonasal transclival, transellar transcavernous, and paramedian approaches to the medial petrous apex has renewed interest in studying the anatomical relations of the abducent nerve from an endoscopic perspective.[7,22] In particular, petroclival tumors tend to grow along a lateral to medial trajectory and can therefore displace the abducent nerve medially. Barges-Coll et al.[7] found that the vertebrobasilar junction was on average 4 mm inferior to the origin of the abducent nerve and served as a good landmark for the cisternal segment in midline approaches. In the lateral transclival and medial petrous apex approaches, the dural entry point of the abducent nerve is just posterosuperior to the upper limit of the lacerum segment of the ICA (C3), and the nerve is at risk for direct or thermal injury during drilling.[7] In the posterior cavernous sinus, the abducent nerve runs parallel to the V1 segment of the trigeminal nerve, and therefore, dissection in the approach via the Meckel cave should not proceed above the V2 segment.[7] Abducent nerve injury during endoscopic endonasal approaches has been well documented.[7,24]

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