Posterior Maxillary Sinus Wall: A Landmark for Identifying the Sphenoid Sinus Ostium

Abstract

Importance: Safe entry into sphenoid sinus is critical in endoscopic sinus and skull base surgery. A number of surgical landmarks have been used to identify the sphenoid sinus ostium during endoscopic endonasal surgery with variable reliability and intraoperative feasibility. Objective: To determine if the posterior wall of the maxillary sinus is a reliable landmark to determine the depth of the sphenoid sinus ostium during anterior to posterior dissection. Design, Setting, and Participants: Prospective study of adult patients undergoing endoscopic sinus surgery between August 2016 and September 2017. Measurements were made intraoperatively between the depth of the posterior maxillary sinus wall and sphenoid sinus ostium. Main Outcomes and Measures: The primary measurement is the distance between the depth of the posterior maxillary sinus wall and sphenoid sinus ostium. Additional data points included age, gender, surgical indication, and primary versus revision endoscopic sinus surgery. Results: Forty-five patients (38% male, 62% female) with an average age of 56 were enrolled, resulting in 88 operated sides. The average distance between the depth of the posterior wall of the maxillary sinus and the sphenoid ostium was 1.5 mm ± 1.4 mm. The most common position of the sphenoid sinus ostium was posterior to the level of the posterior maxillary sinus wall (54%), followed by same level (23%) and anterior (23%). There was no significant difference between different disease states ( P = .75) and between primary and revision cases ( P = .13). Conclusions and Relevance: The posterior wall of the maxillary sinus serves as an adjunctive intraoperative landmark to determine the depth of the sphenoid sinus ostium. While the posterior wall of the maxillary sinus approximates the depth of the sphenoid sinus ostium, the relative position is variable and can be anterior or posterior.

Validity of Sphenoid Ostium in Relation to Posterior Wall of Maxillary Sinus by Computed Tomography

“…Our finding, regarding the difference in depth between the two anatomical sites also agree with the CT based readings of Albahkaly et (12) who have reported an average of 7.5 mm difference in the coronal plane between both sites. A smaller average (1.5 ± 1.4 mm) of the intraoperatively measured distance between SSO and PWMS has been reported by Dedhia et al (13) . They have also mentioned that SSO was not always posterior to PWMS but at the same level in 23 % of investigated sides and at an anterior level to it in 23% of them.…”

“…Second, measurement technique: As previously mentioned, some studies used CT to measure the distance between the SSO and PWMS while others measured it directly through the nasal cavity either intraoperatively or in cadavers. Third, racial variation: Differences among races may be also another explanation as our study and that of Albahkaly et al (12) were done in the Middle East, the studies of Casiano (6) and Dedhia et al (13) were done at USA while patients of Lee (14) study were Korean.…”

“…Different anatomical landmarks have been reported as references for localization of the SSO including medial orbital floor (6) , posteroinferior end superior turbinate (7) , superior margin of choana (8) , nasal spine (9) , sphenovomerian suture (10) and sphenoid skull base (11) . Few studies in literature have investigated the posterior wall of maxillary sinus (PWMS) as a landmark to locate the SSO either radiologically or by direct measurement during surgery or cadaveric dissection (12)(13)(14) .…”