Frontal Angle: A New Predictor of Difficulty in Endoscopic Frontal Sinus Surgery-A Preliminary Computed Tomography Study

Objectives: The possibility of visualization of the frontal sinus during endoscopic surgery depends on 3-dimensional configuration of the frontal sinus opening (FSO). We aimed to determine the prevalence of unfavorable angulation of the lower part of the posterior wall of the frontal sinus and its relation to FSO diameter. Methods: One hundred and twenty-eight computed tomography (CT) scans were retrospectively reviewed to measure (1) the angle between the nasal floor and the plane tangent to the posterior table of the frontal sinus above the most posterior aspect of the anterior buttress (frontal angle, FA) and (2) dimensions of the FSO. Results: The FA ranged from below 30 degrees to 90 degrees. Nearly 13% of sinuses (16.4% of patients) showed FA about 90 degrees, which should enable good visualization of the sinus with the 30 degrees scope after opening and clearing the frontal recess, while 4% (6.25% of patients) showed FA <= 30 degrees. The anterior-posterior diameter (A-PD) was below 5 mm in 17.6% of sinuses (26.6% of patients). There was a significant correlation between FA and A-PD. Unfavorable combination of FA and A-PD (<45 degrees, <5 mm) was present in 5.2% of sinuses (8.6% of patients), and extremely unfavorable combination (<30 degrees, <5 mm) in 0.8% (0.8% of patients). Conclusions: The FA shows great interindividual variability, which is very likely to reflect the possibility of inspection of the frontal sinus. This implies a need for further prospective clinical studies to validate FA as a predictor of difficulty in frontal sinus surgery.