Endonasal Identification of the Orbital Apex

Abstract

Objectives/Hypothesis: To describe anatomical landmarks for endoscopic endonasal approaches to the orbital apex and to measure the distances between those landmarks. Methods: In this anatomic study, the nasal fossae of 30 adult fresh cadavers were dissected (n=60 half-skulls). One double-injected orbit was carefully dissected, mainly focusing on the neurovascular structures. The orbital apex was dissected under endoscopic endonasal visualization in all cases. The distances between the ethmoidal crest and choanal arch to the optic canal (OC) and superior orbital fissure (SOF) were measured and recorded. Results: The sample was predominantly male (63.3%, 19/30 cadavers). The following correlations between measurements according to side were observed: ethmoidal crest to OC, r=0.748 (P=0.0001); ethmoidal crest to SOF, r=0.785 (P=0.0001); choanal arch to OC, r=0.835 (P=0.0001); choanal arch to SOF, r=0.820 (P=0.0001). Conclusions: In the cadavers studied in this sample, the ethmoidal crest and choanal arch were relevant structures and exhibited consistent measurements. Spearman correlation coefficients were greater than 0.7, which is indicative of good correlation between measurements obtained in the skull halves of each cadaver. Comparison of the measurements obtained in different sides showed similar values, with no statistically significant differences in the distances between any of the proposed anatomic landmarks.