Endoscopic Endonasal Anatomical Study of the Cavernous Sinus Segment of the Ophthalmic Nerve

Background: The emergence of endonasal skull base surgery has led neurosurgeons to rediscover the surgical anatomy of this region from a ventral perspective. This cadaveric study analyzes the endoscopic endonasal anatomy of ophthalmic nerve (V1), the ophthalmic division of the trigeminal nerve, from its origin in the middle fossa to its orbital entry via the superior orbital fissure. The authors evaluated its relations with the surrounding cranial nerves and blood vessels, with emphasis on the clinical role of these anatomical correlations during surgery in this region.

Objective: This study aims to describe the anatomical relations of the ophthalmic division of the trigeminal nerve from a ventral perspective with emphasis on surgical applications.

Methods: A total of 30 middle cranial fossae, in 15 adult human cadaveric specimens, were dissected endonasally under direct endoscopic visualization. The ophthalmic nerve (V1) was encountered at its origin from the gasserian ganglion and followed to its orbital entry through the superior orbital fissure in all specimens. The relations of V1 with the other trigeminal branches, as well as with the oculomotor and trochlear nerves, the paraclival and cavernous portions of the internal carotid artery (ICA), and superior orbital fissure (SOF) were documented with high-definition images and analyzed. Measurements of the distance between the superior border of the ophthalmic nerve as it emerges from the gasserian ganglion and the inferior border of the trochlear and oculomotor nerves were obtained. Similarly, the distances between the superior border of the ophthalmic nerve and the internal carotid artery and superior orbital fissure were also measured.

Results: The gasserian ganglion is located just lateral to the paraclival ICA. V1 is the most superior trigeminal branch and runs upward, obliquely, along the middle portion of the lateral wall of the cavernous sinus. V1 joins the oculomotor and trochlear nerves to exit the cavernous sinus and enter the orbit through the SOF. Overall, 10% of the specimens displayed the trochlear nerve running along with the ophthalmic nerve. This finding was dubbed “partnered nerves.” In summary, the findings of this study depict the seemingly unfailing anatomy of the cavernous segment of V1; and confirm, in a quantitative manner, the feasibility of the anteromedial triangle as the main entry avenue into the middle cranial fossa when using the endonasal corridor. DISTANCE A (V1–trochlear nerve) 2.09 mm. DISTANCE B (V1–oculomotor nerve) 3.69 mm. DISTANCE C (V1-ICA) 3.95 mm. DISTANCE D (V1–SOF) 14 mm.

Conclusion: The course of the cavernous segment of the ophthalmic nerve appears constant and no clinically significant variations were observed, rendering it a potentially useful and reliable landmark of the lateral wall of the cavernous sinus. It facilitates identifying the anteromedial triangle, which can be an adequate window to access the intradural middle fossa space from a ventromedial route. Variations in the course of the trochlear nerve occur sparsely; it can travel alongside V1 toward the SOF in a common trajectory.