Over the past century, radiological evaluation of the frontal sinus has been sustained for forensic and clinical purposes [9, 11, 26–28, 30]. Guerram classification system is one of the most popular methods for classifying frontal sinus pneumatization patterns [9]. However, two-dimensional methods are not adequate in estimating the asymmetric and irregular three-dimensional extension of the frontal sinus and cannot provide the depth dimension. With advancements in imaging technology, the frontal sinus is increasingly being studied using three-dimensional reconstruction analysis [11, 21, 28, 30].
Aslier et al. suggested a more reliable and precise method for grouping frontal sinus pneumatization patterns using computed tomography volumetric analysis [28]. In agreement with our results, they found that most frontal sinuses were hyperplastic (44.5%), followed by medium-sized (37.2%), while aplasia was found in 4.1%. We analyzed frontal sinus volume differences in relation to gender, age, and side variations. Significantly higher values were noted in males; however, age did not affect volumetric measurements. In a similar manner to our results, Hacl et al. reported mean volumes of 3.423 mm3 and 3.945 mm3 on the right and left sides, respectively but this difference did not reach statistical significance [11]. In their study, Aslier et al. found that the left frontal sinus volume was significantly larger than the right [28]. Males and young adults had significantly larger frontal sinuses according to Park et al. [21].
Several studies have suggested that certain variations of the anterior skull base may increase the risk of iatrogenic injuries during endoscopic sinus surgery [1, 8, 14, 15, 19, 20, 25]. In 1962, Keros et al. proposed a classification system using the depth of the cribriform plate to determine their vulnerability to iatrogenic injuries [15]. Nevertheless, many authors emphasize that more needs to be evaluated than just the depth of the cribriform plate, since this comprises only the medial portion of the anterior skull base, whereas the lateral portion is angulated [3, 6, 12, 13, 22–24]. Gera et al. predicted the hypothetical iatrogenic injury risk based on the angle formed between the lateral lamella of the cribriform plate and the horizontal plane in continuation with the cribriform plate [8]. Comparing the two methods, Gera classification was found to be more sensitive than Keros classification; however, both measurements demonstrated positive correlations [6, 8, 16, 22, 24].
It is important to consider how the extent of frontal sinus pneumatization affects adjacent structures. Researchers have examined the effect of frontal sinus pneumatization on the height of the anterior skull base and have found that greater pneumatization of the frontal sinus is associated with a deeper cribriform plate, and a deeper cribriform plate increases the risk of surgical complications [2, 4, 6, 10]. We found that frontal sinus volume affects the lateral lamella angle. A larger frontal sinus is associated with a higher angle and a lower risk of iatrogenic injury as a result. In other words, a larger frontal sinus is associated with a deeper cribriform plate (a higher risk situation according to Keros) and a higher lateral lamella angle (a lower risk situation according to Gera) (Fig. 4). Consequently, the anterior skull base must be carefully assessed using both methods.
In accordance with previous studies, Gera class II lateral lamella angles (72.3%) were the most common. Table 4 summarizes the distribution of Gera classification in previous reports [1, 6, 8, 16, 18, 24]. In terms of gender, males had significantly higher angles than females, but many authors did not observe such a difference [1, 8, 16, 18]. Similar to Keşkek et al., age did not influence the lateral lamella angle [16]. Our results show that the left side has a significantly higher lateral lamella angle. Mahdian et al. reported significant differences between the right and left angles [18]. Lawson et al. and Freedman et al. studied over 1000 intranasal ethmoidectomies and found that right-sided operations had more complications [7, 17]. They suggested that the position of a right-handed surgeon performing a right-sided ethmoidectomy may correlate with a higher incidence of right-sided surgical complications. Dessi et al. investigated the asymmetry of the ethmoid roof and found it to be lower on the right side, which may contribute to the higher injury rate [5].
Table 4
The distribution of Gera classification of lateral lamella angles in previous studies
| Author | Sample size | Class I (%) | Class II (%) | Class III (%) |
| Abdullah et al. [1] | 150 | 23.7% | 72.3%, | 4% |
| Fadda et al. [6] | 220 | 17.7% | 77.5% | 4.8% |
| Gera et al. [8] | 190 | 32.6% | 62.7% | 4.7% |
| Keşkek et al. [16] | 385 | 34.7% | 63% | 2.3% |
| Mahdian et al. [18] | 372 | 29.57% | 61.42% | 9.01% |
| Sasmal et al [24] | 600 | 11% | 85% | 4% |
Potential weaknesses of this study are the small sample size and retrospective design. The generalization of the results may be limited by the exclusion of subjects with frontal sinus or skull base pathology or previous surgery; however, these conditions could deform the anatomy and result in imprecise measurements. A future study may investigate how frontal sinus and skull base variations affect intraoperative and postoperative outcomes.
The findings of this research provide a deeper understanding of the complex relationship between the frontal sinus and the anterior skull base. Larger frontal sinuses are associated with higher lateral lamella angles. Studies have also shown that larger frontal sinuses are associated with deeper cribriform plates [2, 4, 6, 10]. A safe surgical approach requires awareness of these anatomical associations. Additionally, several parameters should be measured preoperatively to identify anatomical situations that may lead to complications.