Preoperative Evaluation of the Maxillary Sinus Roof as a Guide for Posterior Ethmoid and Sphenoid Sinus Surgery

Background: The maxillary sinus roof has long been regarded as a reliable reference point for both endoscopic and skull base surgery. Objective: This study was designed to evaluate the maxillary sinus roof as a preoperative guide for posterior ethmoid and sphenoid sinus surgery. Method: This was a cross-sectional observational study of 50 randomly selected computed tomographic (CT) sinus scans from patients previously seen at a tertiary rhinology clinic. Each side of the sinuses was treated independently, giving a total of 100 sides for analysis. Using the medial maxillary sinus roof as a fixed reference point, the vertical distance to the posterior ethmoid skull base, natural sphenoid ostium, and anterior sphenoid roof and floor were measured. In addition, the maxillary sinus to posterior ethmoid height ratio was calculated for each patient. Results: Relative to the medial maxillary sinus roof, the mean vertical height of the posterior ethmoid skull base was 14.08 +/- 3.03 mm. Using this same reference point, the mean vertical distance to the natural sphenoid ostium, sphenoid roof, and sphenoid floor was 2.76 +/- 2.80 mm, 12.18 +/- 3.20 mm, and 5.94 +/- 2.94 mm, respectively. The mean maxillary sinus to posterior ethmoid height ratio was 2.49:1. Conclusion: The medial maxillary sinus roof is a reliable preoperative reference point for guiding safe surgical entry into the posterior ethmoid and sphenoid sinus. In addition to providing a margin of safety away from the skull base, it may also help with localization of the natural sphenoid ostium. A classification scheme for evaluating posterior ethmoid height is proposed.