Anatomical Variants and Landmarks for the Anterior Ethmoid Artery: A Study of CT Imaging

Introduction: The anterior ethmoid artery (AEA) is commonly encountered in sinus surgery and endoscopic surgery of the anterior skull base. Visual location of the vessel along the skull base can be difficult, particularly in the setting of neoplasia, inflammation, and bleeding. Injury can be problematic and may result in intraorbital bleeding and hematoma, threatening the eye, or even intracranial bleeding. Our study reviewed the course of the AEA as it traverses the fovea ethmoidalis, with the aim of devising a method of locating the vessel during endoscopic surgery.

Methods: A retrospective study of CT imaging of patients in an outpatient clinic of a tertiary referral center was undertaken. Fifty CT scans with multi-planar reconstructions of the paranasal sinuses were reviewed to study the course of the AEA in three planes across the fovea ethmoidalis. The path of the AEA was recorded in relation to ethmoid lamellae posterior to the frontal sinus (or frontonasal drainage pathway), both laterally (adjacent to the orbit) and medially (adjacent to the lateral lamella of the cribiform plate). The course was also documented to be either along the skull base, below the skull base along the entire course, or only below the skull base laterally. Data were then analyzed to assess for common findings and patterns.

Results: Fifty CT scans were assessed. In three patients, the course of the AEA on both sides could not be confidently identified. These patients were found to have severe inflammatory disease with neo-osteogenesis or osteolysis. In one patient, the AEA could not be seen on one side. In total, 93 AEAs were identified, and the course traced across the skull base. The most common pathway of the AEA was passage of the vessel along the second ethmoidal lamella posterior to the frontal sinus os or frontonasal drainage pathway. This finding was present in 40/93 (43%). The next most common finding was for the AEA to be situated at the second lamella laterally, and to pass anteriomedially to be situated between the first and second lamella medially. This finding was present in 15/93 (16.1%). The AEA was found to traverse along the first ethmoidal lamella in 9/93 (9.7%). The vessel passed entirely along the skull base in 58/93 (62.4%). In 26/93 (28%), the AEA was below the skull base; in 9 cases (9.7%), the vessel was found below the skull base laterally but at the level of the skull base medially.

Conclusion: In most cases, the AEA can be accurately located in relation to the skull base at the fovea ethmoidalis using three-planar images from a CT scan. This information can be used to locate the vessel during endoscopic surgery. Our study has demonstrated that the artery is most commonly associated with the second bony lamella (58/93, 62.4%) and can be found at or between the first and second lamellae in 84/93 (90.3%).