International assessment of inter- and intrarater reliability of the International Frontal Sinus Anatomy Classification system.

Background: Inconsistencies in the nomenclature of structures of the frontal sinus have impeded the development of a validated "reference standard" classification system that surgeons can reliably agree upon. The International Frontal Sinus Anatomy Classification (IFAC) system was developed as a consensus document, based on expert opinion, attempting to address this issue. The purposes of this study are to: establish the reliability of the IFAC as a tool for classifying cells in the frontal recess among an international group of rhinologists; and improve communication and teaching of frontal endoscopic sinus surgery (ESS).

Methods: Forty-two computed tomography (CT) scans, each with a marked frontal cell, were reviewed by 15 international fellowship-trained rhinologists. Each marked cell was classified into 1 of 7 categories described in the IFAC, on 2 occasions separated by 2 weeks. Inter- and intrarater reliability were evaluated using Light's kappa (κ), the interclass correlation coefficient (ICC), and simple proportion of agreement.

Results: Interrater reliability showed pairwise κ values ranging from 0.7248 to 1.0, with a mean of 0.9162 (SD, 0.0537). The ICC was 0.98. Intrarater reliability showed κ values ranging from 0.8613 to 1.0, with a mean of 0.9407 (SD, 0.0376). The within-rater ICC was 0.98.

Conclusion: Among a diverse sample of rhinologists (raters), there was substantial to almost perfect agreement between raters, and among individual raters at different timepoints. The IFAC is a reliable tool for classification of cells in the frontal sinus. Further outcome studies are still needed to determine the validity of the IFAC.