International Frontal Sinus Anatomy Classification and Anatomic Predictors of Low-Lying Anterior Ethmoidal Arteries

Background The International Frontal Sinus Anatomy Classification (IFAC) was introduced to more accurately characterize ethmoid and frontal sinus pneumatization patterns. The prevalence of IFAC cells and their anatomic associations have not been described. Objective The goal was to examine the prevalence of IFAC cells and determine radiologic features associated with a low-lying anterior ethmoidal artery (LAEA). Methods Imaging of adult patients who underwent computed tomographies from January 2015 to March 2016 were retrospectively reviewed by using the IFAC classification. We also measured the distance from the skull base to the anterior ethmoidal artery (AEA), the height of the lateral lamella of the cribriform plate, and anterior-posterior diameter from the anterior wall of the frontal sinus to the skull base (APF). Patients with a history of sinus surgery, trauma, malignancy, or congenital anomaly were excluded. Statistical analysis was performed by using Pearson correlation coefficients and χ2 tests. Results A total of 95 patients met the inclusion criteria. There was a significant association between supraorbital ethmoid cells and an LAEA (p < 0.001), with a significant effect size (ϕ = 0.276, p = 0.007). An inverse relationship was observed between Keros type I classification I and an LAEA (p < 0.001), with a significant effect size (ϕ = -0.414, p = 0.000). Significant associations were found between the AEA distance from the skull base and the cribriform lateral lamella height (R = 0.576, p < 0.001). In addition, there was a significant association between the AEA distance from the skull base and the APF (R = 0.497, p < 0.001). Conclusion The presence of a supraorbital ethmoid cell and a wide APF were associated with an LAEA. There was a significant relationship between Keros type I classification and the AEA adjacent to the skull base. Delineation of these anatomic relationships may be helpful during endoscopic sinus surgery to avoid complications.