In the current study, we determined the prevalence, symmetry, and interrater agreement of IFAC cell types in an adult population with non-diseased sinuses. To date, a few studies have documented the prevalence of FR cells using the IFAC in different populations with healthy sinuses [2, 3, 10, 12, 13]. The most frequently observed FR cell in our study was ANC, present in 88% of sides, consistent with previous literature quoting ANC incidence between 87–97%. Given its high prevalence, ANC serves as a reference cell for all anteriorly-based cells in the IFAC system and is a crucial consideration in endoscopic frontal sinus surgery. The second most prevalent cell in our study was SBC, followed by SAC, FSC, SOEC, SAFC, and SBFC in descending order. The prevalences of SAC, SBFC, and SOEC in our study were comparable to previous studies, while the prevalences of SAFC and SBC were lower. Our results confirm that the prevalence of individual FR cells other than ANC can vary significantly across different populations. Apart from that, variations in the numbers of males and females across the studies might affect the overall prevalence rates.
In endoscopic frontal sinus surgery, the presence of FR cells that pneumatize throughout the frontal sinus, such as SAFC, SBFC, and SOEC, can pose challenges and often require alternative procedures, such as the axillary flap procedure, the endoscopic modified Lothrop procedure, or an external approach [18]. Our study found that at least one such cell was present in approximately 29% of FRs, which is consistent with Gotlib et al.'s study [3], which reported a rate of 28%. Additionally, we observed that these cells were more prevalent in male patients, likely due to their frontal sinuses being more pneumatized [9].
Our analysis revealed that SBFC had the highest incidence of presence or absence on both sides, followed by SAFC, ANC, SOEC, SAC, and SBC. We found that the incidence of bilateral presence was high for ANC and SBC, which was consistent with the results of Choby et al.'s study [2]. However, when we investigated the probability of a cell's contralateral presence when present on the ipsilateral side, we found that SBFC had the highest probability. In contrast, Choby et al.'s study reported that the SOEC had the highest probability. In both studies, SAC had the lowest probability of contralateral presence.
Our analysis showed that there was a high level of inter-observer agreement between two independent reviewers for nearly all IFAC cell types. Among the different cell types, the FSC demonstrated the highest level of agreement among reviewers, while the SAFC had the lowest. Choby et al. [2] also found good to excellent interrater agreement in their evaluation of one hundred CT scans. However, they reported that the SAC had the highest reliability among reviewers, whereas the SBFC had the lowest. The authors noted that the difficulty in distinguishing between the ethmoid skull base and the posterior plate of the frontal sinus could lead to the misidentification of some cells. In another study, Villarreal et al. [16] reported substantial to almost perfect agreement among 15 rhinologists from various centers. They found that the inter-observer agreement was slight for the SAC and SBC, fair for the SBFC and SOEC, and moderate for the ANC, SAFC, and FSC. However, in this study, the authors used sets of selected images with specific types of FR cells marked, rather than multiplanar reconstruction with adjustable planes. Our findings, combined with those of Choby et al., suggest that triplanar analysis of a fine-cut CT examination can aid in accurately identifying FR cells.
The present study has several limitations that need to be acknowledged. First, the ethnic composition of our research sample may limit the generalizability of our findings. Second, the study was not conducted across multiple centers, which may result in the neglect of potential local populational differences. Another limitation is that the CT scans were restricted to patients with healthy paranasal sinuses, which might have led to an underestimation of the exact prevalence of FR cells. However, since the number of patients with sinunasal disease in the hospital radiology database is expected to be higher than in the general population, the frequency of FR cells in these patients may differ. If such patients were included in the study, the results may have been more contradictory. Furthermore, a recent study indicated that individuals with advanced sinus disease had a significantly higher chance of inaccurate identification of the FR cell [4]. Lastly, while two independent observers analyzed the CT data and the results were compared and reviewed, the interpretation is always subjective, which represents a final limitation. Despite the limitations, our study utilized a considerable number of CT scans with a fine-cut slice thickness and employed multiplanar reconstruction with adjustable planes. We are confident that our findings make a significant contribution to estimating the prevalence of IFAC cells globally and pave the way for further studies on different ethnic groups. Additionally, by providing prevalence data on FR cells in individuals with healthy sinuses, our findings can serve as essential reference data for future studies examining the possible link between IFAC cells and frontal sinusitis.