Intraconal Anatomy of the Anterior Ethmoidal Neurovascular Bundle: Implications for Surgery in the Superomedial Orbit

Abstract

Background The anterior ethmoidal artery (AEA) branches from the ophthalmic artery in the superomedial intraconal space. The feasibility of management of lesions arising from the superomedial intraconal space via an endoscopic endonasal approach has not been sufficiently explored. Objective To yield a detailed anatomic description of the anterior ethmoidal neurovascular bundle and its variants to serve as the foundation for possible management of lesions in the superomedial intraconal space. Methods Eight cadaveric specimens (16 sides) were dissected using an endonasal approach, tracing the AEA proximally through the superomedial intraconal space. Furthermore, the anatomy of adjacent structures was noted, and distances from the anterior ethmoidal foramen to the origin of the AEA at the ophthalmic artery were measured. Results Supraorbital cells were found in 13/16 sides (81.25%), and a bony dehiscence of the anterior ethmoidal canal was observed in 5/16 sides (31.25%). The nasociliary nerve, ophthalmic artery, superior division of the oculomotor nerve, superior rectus muscle, and levator palpebrae superioris were routinely identified in the superomedial intraconal space. The AEA passed through a corridor between the medial rectus and superior oblique muscles after arising from the ophthalmic artery (lateral to the foramen) in all specimens. The average distance from its origin to the anterior ethmoidal foramen was 5.19 ± 0.98 mm. Conclusion Anatomically, it is feasible to access the superomedial intraconal space via an endoscopic endonasal approach. This study provides the anatomical basis for procedures in the superomedial intraconal space.

Endoscopic Endonasal Approaches to the Medial Intraconal Space: Comparison of Transethmoidal and Prelacrimal Corridors

“…6 Description of technical nuances and the advantages and drawbacks of the transethmoidal and prelacrimal approaches are helpful to choose the appropriate corridor for addressing lesions in specific zones within the medial intraconal space. 17,18 Subdivision of the medial intraconal space into three distinct zones helps selecting the optimal endonasal approach. Although both the transethmoidal approach and the prelacrimal approach can provide good exposure of Zone 3 (below the lower border of medial rectus muscle, average height 6.53 AE 0.59 mm), lesions arising from the medial intraconal space restricted to Zone 3 are rare.…”

“…Whereas it is reasonable to use a transethmoidal approach for incision and drainage of an abscess or a tumor biopsy, its use for tumor resection or control of a retracted artery, is extremely limited by the poor instrument maneuverability through a narrow space and the risk of damaging the optic nerve. 18 In addition, although structures in Zone 1 could be exposed through a prelacrimal approach on cadaveric specimens, the orbital fat in Zone 3 and Zone 2 needs to be removed or retracted and strict control of the vessels are critical for the exposure, which may be detrimental to ocular function. Therefore, a prelacrimal approach might be indicated as an auxiliary corridor for resection of lesions that originated in Zone 3 or 2 with superior extension.…”

“…[16][17][18] On previous cadaveric studies, partial resection of the orbital floor via a transnasal prelacrimal approach provided a corridor to access the inferior intraconal space, 16,17 and a transethmoidal approach was advocated to access the superomedial intraconal space. 18 Although both the transethmoidal and prelacrimal approaches can access the inferomedial intraconal space, technical nuances, advantages and drawbacks for each approach have not been sufficiently explored. Moreover, whether the prelacrimal approach may be suitable for managing lesions in other regions of the medial intraconal space is undefined.…”

Expanded exposure and detailed anatomic analysis of the superior orbital fissure: Implications for endonasal and transorbital approaches

“…After traversing the medial SOF, the CNs VI, V 1 , and III enter the intraconal space, innervating their respective recti and oblique muscles or glands. 26 The CN VI runs an oblique course traveling in a lateral direction to innervate the lateral rectus muscle while crossing the SOF. Moreover, the distal segments of the CN III, optic nerve, ophthalmic artery and nasociliary nerve within the medial intraconal space could be sufficiently exposed via a transnasal corridor.…”

“…The terminal segment of the CN IV and the frontal nerve were identified at the dorsal aspect of the levator palpebrae superioris. 26 Although these structures could be sufficiently exposed through the gap between the superior oblique and medial rectus muscles on a cadaveric dissection, the employment of an endonasal corridor to address lesions arising from the SOF with extension into the dorsal aspect of the levator palpebrae superioris is extremely limited on live patients. It may serve as an auxiliary corridor for tumor biopsy or abscess drainage; to act as a reasonable window for tumor resection or bleeding control, however, is not recommended.…”