Endoscopic Endonasal Approach to the Inferolateral Intraconal Orbit: An Anatomical Analysis of Exposure and Maneuverability.

Background: Endoscopic endonasal techniques, initially developed for sinonasal tumor resection, have revolutionized the approach to orbital lesions. The emergence of endonasal orbital tumor surgery has prompted anatomical studies focusing on the medial orbit, yet there remains a lack of literature on maneuverability lateral to the optic nerve (ON), with current feasibility assessments relying primarily on the plane of resectability (POR).

Methods: Bilateral anatomical dissections were conducted on four latex-injected human cadaveric heads using an endoscopic medial and inferior orbitotomy and superomedial displacement of the inferior rectus muscle (IRM) to access the inferolateral intraconal quadrant. Measurements of distances, areas, angles of attack, and volumetric exposure were obtained using stereotactic points from an imaging-based navigation system. Additionally, an illustrative case was presented to demonstrate the endoscopic management of laterally based intraconal lesions.

Results: The intraconal space was safely accessed through superomedial displacement of the IRM. The mean intraconal volumetric exposure attained through this maneuver was 2.78 cm³ (1.18 cm³). The most superolateral point reachable by the ipsilateral endoscopic endonasal approach was consistently lateral and superior to the ON at a mean absolute distance of 1.45 cm (0.37 cm). Maneuverability at this target point was superior in the sagittal plane, noted by a larger vertical angle of attack compared with the horizontal angle of attack.

Conclusion: This study demonstrates that inferolateral intraconal dissection through an ipsilateral endoscopic endonasal approach is feasible via a medial orbitotomy and superomedial retraction of the IRM. Additionally, our findings reaffirm lesions below the POR are suitable for endoscopic endonasal resection.