Discussion
A comprehensive understanding of the anatomical variations and pathologies of the maxillary sinus is essential for clinical practice in dentistry, maxillofacial surgery, and otolaryngology. Various imaging techniques, including CT and CBCT, have been used to assess the nasal cavity and maxillary sinuses. Conventional radiographs offer only a two-dimensional view of anatomical structures. By contrast, CT and CBCT provide valuable insights for imaging and identifying anatomical variations within the bony structures of the paranasal sinuses (2,3). MSV and sinus dimensions may vary by age and between individuals. Additionally, even within the same individual, there may be variations between the right and left sinus parameters (2). The relatively high prevalence of maxillary sinus asymmetry (62.6%) and the variability in other parameters in this study may be influenced by several anatomical, developmental, and environmental factors. Craniofacial morphological variations, particularly vertical skeletal growth patterns, have been shown to affect sinus dimensions and contribute to side-to-side differences in MSV (10). Ethnic and population-specific variability further contributes to these differences, as studies in other populations report wide variation in sinus asymmetry prevalence, depending on methodology and population (5,6,11). Developmental factors, including differential pneumatization and sinus remodeling influenced by dental status, skeletal growth, and sinonasal anatomy, may also play a role (12). Environmental and functional influences, such as chronic sinonasal inflammation or differences in mastication patterns, can contribute to asymmetric sinus development over time (13). Finally, methodological factors, including imaging modality, slice orientation, and the threshold used to define asymmetry, may partly explain differences in prevalence across studies. The prevalence of AMO in the present study (~48%) has important anatomical and clinical implications. AMO has been consistently associated with impaired mucociliary clearance, mucus recirculation, and a higher risk of recurrent or chronic maxillary sinusitis (14). Generally, AMO prevalence ranges from 35-56% and is significantly associated with abnormal maxillary sinus mucosal changes, such as mucosal thickening or natural-ostium obstruction (15). This pathophysiological mechanism suggests that AMO may facilitate mucus recirculation between the accessory and natural ostia, predisposing the sinus to chronic inflammation and recurrent sinusitis (16). In our study population, the high prevalence of AMO underscores the importance of careful preoperative imaging assessment for ENT surgeons, radiologists, and dental/maxillofacial clinicians to minimize procedural complications and anticipate potential sinus drainage issues.
In the present cohort, maxillary sinus septations were identified in approximately one-fifth of patients (~20%). This finding aligns with reported prevalence rates from CBCT and CT studies, which range from 21 to 25.6% of sinus segments and 25-37% of individuals, depending on the population and imaging method employed (17,18). Anatomically, these septa comprise bony ridges that divide the sinus cavity, often oriented bucco-palatally and located in the middle region, which complicates surgical access (18). Clinically, the presence of septa significantly increases the risk of perforating the Schneiderian membrane during sinus lift procedures. A meta-analysis across 1,865 patients (2,168 sinus lifts) found an odds ratio of ~4.03 for perforation when septa were present, compared with sinuses without septa (19).
Congenital maxillary sinus hypoplasia was identified in 1% of the cases in this study, consistent with the low prevalence reported in the literature (5.65%) (20). It is clinically significant because it may mimic chronic maxillary sinusitis, present with nonspecific symptoms, or lead to diagnostic confusion on routine imaging. In addition, the altered anatomy may complicate endoscopic sinus surgery, increase the risk of orbital penetration, and affect surgical planning (20). Therefore, even though its prevalence is low, awareness of this variation is essential for accurate radiologic interpretation and safe surgical management.
Certain studies indicated a significant association between age and MSV, noting that MSV decreases with age (21,22). By contrast, others reported no significant differences between the right and left MSV values and MSV with age (21,23,24). Sex differences in MSV have also been explored. Aşantoğrol and Coşgunarslan (2) and Al-Rawi et al (23) observed that males had greater maxillary sinus width, height, and length than females, with statistically significant differences. Conversely, Demir et al (25) and Lessa et al (4) reported no significant correlation between MSV and sex. Despite these findings, numerous studies support that MSV values are generally higher in males than in females (21,23). In the present study, the right MSV did not vary significantly with age, whereas the left MSV showed differences across age groups. Concerning sex, the MSV on both sides was significantly higher in males than in females, with this difference evident across age categories.
Accurate identification of bony septa is essential to enhance the safety of surgical procedures, particularly sinus lift surgeries and implant placements, as septa have been associated with an increased risk of sinus membrane perforation and thinner sinus mucosa. This risk is heightened when the septa are arranged longitudinally or are incomplete, as these configurations can complicate membrane elevation compared with a transverse arrangement (4). In terms of anatomical variations, previous studies found no association between the presence of septa and MSV. However, significant increases in the maxillary sinus width on both the left and right sides were noted when septa were present (2,21). The prevalence of bony septa within the maxillary sinus has been reported to range from 9.5 to 70%, varying according to the studied population and diagnostic modality used (26). Lessa et al (4) observed that 47% of maxillary sinuses presented with bony septa, although no significant difference was noted in MSV related to the presence of septa. Şimşek Kaya et al (27) identified septa in 32.9% of 228 evaluated sinuses, while Asan et al (3) reported a prevalence rate of 24%, with septa more commonly located on the right side. Sex differences in septa prevalence have been inconsistent in the literature. A study found a higher prevalence of septa among females, with no association between septa and age or dental status (28). Conversely, studies by Koymen et al (29) and Hong et al (30) reported a male predominance in septa presence. This increased occurrence in males has been postulated to relate to the typically higher mean maximum bite force in males than females (29,30). In the present study, maxillary sinus septation was identified in 45 cases (19.8%), comprising 26 males (57.8%) and 19 females (42.2%). Bilateral septation was the most common in 19 cases (42.2%).
Haller cells, or infra-orbital ethmoid cells, are air-filled cavities inferolateral to the ethmoidal bulla (3). These cells can increase susceptibility to sinus pathologies by accelerating inflammation, complicating sinus surgery, and contributing to conditions such as rhinosinusitis. Infection of Haller cells can lead to mucosal swelling, which restricts secretion transport and creates a cycle that may contribute to unilateral orbital cellulitis (3). Prevalence rates of Haller cells vary widely in the literature, with reports ranging from 4.7 to 45.1% or 5.5 to 45.9% (31,32). Asan et al (3) observed Haller cells in 15.3% of samples, identifying them as the second most significant anatomical variation. Although there was no significant difference in prevalence between sexes, a higher occurrence was noted on the right side (3). Chaudhari et al (32) found a prevalence of 10% (30 out of 300 individuals), with 18 males and 12 females, yielding a male-to-female ratio of 3:2. Conversely, Ahmad et al (33) reported a notably higher prevalence of 38.2%, with a higher occurrence among females (32). Regarding laterality, Chaudhari et al (32) reported that Haller cells appeared bilaterally in 16 cases and unilaterally in 14, suggesting a tendency for bilateral occurrence. This finding contrasts with a previous study that reported a predominantly unilateral presentation of Haller cells (34). The current study identified Haller cells in 23 cases (10.1%), comprising 14 males and 9 females. The majority of these cases were unilateral (87%) and predominantly located on the right side (52.2%), consistent with the findings of Ramaswamy et al (34) and Asan et al (3). The most prevalent anatomical variation observed was sinus asymmetry, identified in 142 cases (62.6%). Conversely, the presence of Haller cells was the second least common variation. This finding contrasts with the study by Asan et al (3), who identified Haller cells as the second most frequent anatomical variation.
Lantos et al (35) defined infraorbital canal (IOC) protrusion as occurring when the entire 360˚ circumference of the IOC wall lacked contact with a maxillary sinus wall on at least one axial CT image. Although reported prevalence rates for ION protrusion range from 8 to 35%, there is no standardized definition for protrusion despite efforts to establish a classification system (35). In their study, Lantos et al (35) observed a 10.8% prevalence of IOC protrusion into the maxillary sinus, with a bilateral protrusion rate of 5.6% (34). Eiid et al (36) found that the IOC most frequently presented as the typical confined type, detected in 78.1% of sinuses, while the suspended (or protruded) variant was identified in 14.6% of cases. They emphasized that IOC protrusion, though not uncommon, requires heightened caution from surgeons utilizing the maxillary sinuses as access points, particularly in the upper lateral areas of the sinus (36). In the present study, ION protrusion into the maxillary sinus was present in 62 cases (27.3%), with bilateral protrusions in 40 cases (17.6%). On both sides, ION protrusion was significantly associated with increased MSV. The observed association between ION protrusion and increased MSV in our study has important anatomical and clinical implications. Previous volumetric research demonstrated that individuals with a ‘descending’ or protruding IOC Type 3 consistently exhibit significantly larger MSVs, suggesting that extensive sinus pneumatization may progressively encompass or suspend the canal within the sinus cavity. Since the developmental trajectory of the ION canal is established prenatally, whereas maxillary sinus pneumatization continues through adolescence and adulthood, this relationship supports the concept that ION protrusion is likely a pneumatization-driven variant rather than an isolated anomaly (37). Clinically, larger sinuses have been associated with a higher prevalence of canal exposure or ‘suspension’ into the sinus lumen, reported in ~11% of cases in large CT-based series, underscoring the risk of iatrogenic nerve injury during endoscopic sinus surgery, dental implant placement, or transmaxillary procedures (35). Therefore, these findings reinforce the importance of preoperative imaging, particularly volumetric assessment, in patients exhibiting large maxillary sinuses, as the likelihood of encountering a protruding or vulnerable IOC is increased. This relationship also highlights the need for future research to routinely incorporate sinus volume when evaluating ION canal variants to improve anatomical understanding and surgical planning.
The small sample size, non-random sampling, no multiple comparison analysis, lack of assessment of interobserver reliability, the use of ellipsoid volume estimates, and the data being collected from only a single center are significant limitations of this study that may affect the generalizability of the findings.
In conclusion, anatomical variations of the maxillary sinus were common within the study population, with asymmetry present in 62.6%. The maxillary sinus was revealed to be significantly larger in males than in females, exhibiting notable differences in dimensions and volume. Additionally, this study revealed an association between ION protrusion and sinus volume; specifically, sinuses with protruded ION tended to have larger volumes. These findings suggest the potential necessity for preoperative assessments utilizing CT scans or other three-dimensional imaging techniques.