Computed tomographic evaluation of anatomic relationship between the paranasal structures and orbital contents for endoscopic endonasal transethmoidal approach to the orbit.

OBJECTIVE: Some recent reports have described the endoscopic endonasal removal of orbital tumors. However, the surgical anatomy for an endoscopic endonasal approach has not yet been clearly described. The first aim of this study is to examine the anatomic relationship between the paranasal and orbital structures with the use of computed tomographic imaging and to find useful landmarks for a transethmoidal approach to the orbital retrobulbar space. The second aim is to determine a procedure to minimize the possibility of bleeding via the endonasal transethmoidal approach.
METHODS: One hundred axial and coronal computed tomographic scans obtained between January 2004 and December 2005 were evaluated.
RESULTS: The third lamella was located posteriorly to the posterior end of the eyeball on all axial computed tomographic scans, thus indicating that it may be a useful landmark for the localization of the retrobulbar space. There was a large variation in the relationship among the inferior and medial rectus muscles and the ethmoid-maxillary plate regarding their location. These results demonstrate that the route into the orbit via the ethmoid-maxillary plate gains no access to the medial side of the medial rectus muscle, the region with abundant blood vessels.
CONCLUSION: These results suggest that the third lamella and ethmoid-maxillary plate are the most important anatomic landmarks for an endoscopic endonasal transethmoidal approach to the orbital retrobulbar space.