A stepwise surgical technique using the medial orbital floor as the key landmark in performing endoscopic sinus surgery

Hypothesis: The medial orbital floor (MOF) and adjacent bony ridge of the antrostomy, when combined with columellar measurements, are easily identifiable and consistent anatomic reference points from which critical orbital and skull base structures can be found during endoscopic sinus surgery. Methods: Two examiners, with varying endoscopic sinus surgery experience, performed endoscopic and direct measurements from the columnella and medial orbital floor to critical orbital and skull base structures on 11 human cadaver heads (18 sides). The distances to four critical skull base or orbital structures and to the anterior and posterior wall of the sphenoid sinus were measured. The mean, ranges, and standard deviations for all measurements (endoscopic and direct) were calculated and simple regression analysis was performed. Results: The mean and range of values for each of the variables correlated well between examiners, and between endoscopic and direct measurements. There was slightly more variability in measurements when the MOF was used. However, the differences were no more than a few millimeters and did not appear to affect the overall clinical use of these values. Conclusions: The MOF and adjacent bony ridge of the antrostomy, when combined with columellar measurements, are easily identifiable and consistent anatomic landmarks that are not affected by the presence of significant inflammatory disease or previous surgery. These reference points provide even the most inexperienced surgeon with precise anatomic localization within the paranasal sinuses. They also determine the correct anteroposterior trajectory into the sphenoid sinus, whereby inadvertent intracranial or intraorbital complications may be avoided.