The Oculomotor Nerve: Microanatomical and Endoscopic Study

OBJECTIVE: This study was performed to assess the anatomy of the oculomotor nerve and to describe its course from the brainstem to the orbit. A new anatomically and surgically oriented classification of the nerve has been provided to illustrate its topographic and neurovascular relationships. METHODS: Fifty-nine human cadaveric heads (118 specimens) were used for the anatomical dissection. Forty-four of these were embalmed in a 10% formalin solution for 3 weeks, and 15 were fresh frozen injected with colored latex. The nerve was exposed along its pathway via frontotemporal, frontotemporo-orbitozygomatic, and subtemporal transtentorial approaches. These approaches were performed to expose each segment of the nerve. An endoscopic endonasal transsphenoidal approach was performed on 9 heads to visualize and compare the neurovascular relationships of the same areas from an inferomedial perspective. Measurements of each segment of the nerve were taken in all specimens during the dissecting process. RESULTS: The nerve was divided into 5 segments: cisternal, petroclinoid, cavernous, fissural, and orbital. The simultaneous use of a microscopic transcranial and an endoscopic endonasal route allows a better understanding of the spatial relationship of the nerve. CONCLUSION: The knowledge of the dural, bony, and neurovascular relationships of the oculomotor nerve may help to prevent common complications during both microsurgical and endoscopic approaches to the cavernous sinus, interpeduncular, middle cranial fossa, and orbital regions. We discuss the possible significance of the observed anatomical data and propose classification of the different segments of the nerve.