Positional Relationship of Ethmoidal Foramens With Reference to the Nasion and Its Significance in Orbital Surgery.

PURPOSE: The aim of the study was to elucidate the positional relationship of the ethmoidal foramens (EFs) with reference to the nasion to facilitate prediction of the exact location of EFs, the optic canal (OC), and the frontoethmoidal suture (FS), and thereby avoid complications during complex surgery involving the medial wall of the orbit. MATERIALS AND METHODS: One hundred two intact orbits of 57 embalmed cadavers were dissected in this observational anatomic study. Nasion' (N') was defined as the intersection point of the medial orbit margin with the horizontal line through the nasion, and this was used as a reference point. N'-OC was defined as the straight line joining N' and OC. The locations of the anterior ethmoidal foramen (AEF), posterior ethmoidal foramen (PEF), and OC were determined with reference to N'. The vertical distances from N'-OC to EFs and to FS were also determined. RESULTS: The N'-AEF, AEF-PEF, and PEF-OC distances were 18.4, 15.3, and 8.3 mm, respectively. Vertically, AEF and PEF were situated at 0.2 mm below and 0.4 mm above N'-OC, respectively. At the same reference points, N'-OC was situated at 0.4 and 0.6 mm above FS, respectively. CONCLUSIONS: N', AEF, PEF, and OC were considered to be situated on the same straight line, and N'-OC could be regarded as coinciding with FS. This means that N' is an easily identifiable and reliable landmark for identifying EFs, OC, and FS. Our navigational parameters with reference to N' will help surgeons to enhance the safety of orbital surgery.