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

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.

Radiological anatomy of the anterior ethmoidal artery for functional endoscopic sinus surgery

Aim:This study investigated the extent to which the anterior ethmoidal artery and anterior ethmoidal foramen could be reliably identified on routine coronal sinus computed tomography scans. Where they could be identified, the relationship of these structures with the vertical height of the skull base, and their distance from an anterior landmark, were measured.Methods:Fifty consecutive coronal sinus computed tomography scans were viewed independently by two observers. Scans were reviewed when the observers' opinions differed.Results:Inter-observer concordance was high. The anterior ethmoidal foramen was visualised in 95 per cent of cases bilaterally and in the remaining 5 per cent unilaterally. The anterior ethmoidal artery was visualised in 33 per cent of scans. The anterior ethmoidal foramen was at skull base level in 72 per cent of sides studied, and below it in the remainder. The distance from the lacrimal crest to the anterior ethmoidal foramen was 22.4 mm (mean; standard deviation 3.7).Conclusion:The anterior ethmoidal foramen is a reliable landmark on coronal computed tomography scans of the paranasal sinuses. From this, the position of the anterior ethmoidal artery can be inferred.

Anterior Ethmoidal Artery: Microsurgical Anatomy and Technical Considerations

OBJECTIVE: Vascular lesions of the anterior cranial fossa can receive significant blood supply from the anterior ethmoidal artery. Embolization of this blood supply exposes the parent vessel, the ophthalmic artery, to possible embolic complications, which can lead to loss of vision. A study of the microsurgical anatomy can help delineate the course of the anterior ethmoidal artery and find the best points for proximal control of the blood supply to these lesions. Clinical cases are presented to illustrate how lesions with prominent anterior ethmoidal artery feeders are best approached through fronto-orbital single-flap craniotomies. METHODS: Eight cadaveric dissections to demonstrate the microsurgical anatomy of the anterior ethmoidal artery were performed to study the relevant anatomy. Two clinical cases are presented that demonstrate clinical application of this anatomy through fronto-orbital single-flap craniotomies. RESULTS: Eight arteries were studied in four cadaveric heads. The dissections show the course of the anterior ethmoidal artery from the ophthalmic artery in the orbit, through the anterior ethmoidal foramen into the ethmoid air cells, to the cribriform plate, where it turns superiorly to become the anterior falx artery. The first surgical case is of a giant tuberculum sellae meningioma that was resected with coagulation and division of the anterior ethmoidal arteries at the anterior ethmoidal foramina at the laminae papyraceae of both medial orbital walls. The second surgical case is of a large deep right frontal arteriovenous malformation that was resected with coagulation and division of the anterior ethmoidal artery at the anterior ethmoidal foramen of the lamina papyracea of the right medial orbital wall. CONCLUSION: The cadaveric dissections and our surgical experience show that the anterior ethmoidal artery has three important sites for surgical access: 1) the anterior ethmoidal foramen at the lamina papyracea of the medial orbital wall; 2) the anterior ethmoid canal at the lateral ethmoid wall; and 3) extradurally, at the cribriform plate. These three sites are best accessed through a fronto-orbital single-flap craniotomy, which can be unilateral or bilateral, depending on the pathological findings. The described orbital-cranial approach in this article is not being advocated to replace the standard pterional and frontal approaches; rather, we suggest it as an option in these complex cases that require early proximal control of the anterior ethmoidal artery feeders.