Radiodiagnostic properties of maxillary antroliths: a retrospective cone beam computed tomography study

Abstract

Background

To evaluate the frequency and radiodiagnostic characteristics of maxillary antroliths using cone beam computed tomography.

Methods

A review of 1166 patients aged 11–85 years was conducted to assess the frequency of maxillary antroliths, considering sex, age, and location. The relationship between antroliths and sex, location, dental treatment status, and sinus inflammation was evaluated. The shape, size, and volume of the antroliths were also analyzed. Data were analyzed using descriptive statistics, Mann-Whitney U, Kruskal-Wallis, Spearman rank correlation, independent t-tests, and Pearson Chi-square tests.

Results

Forty-eight antroliths were detected in 41 patients (3.5%), with 16 in males and 25 in females. The frequency of antroliths was higher in the 81-90- and 31-40-years age groups (p < 0.001). The most common locations were the sinus floor (56.3%) and molar region (87.5%), with an amorphous shape (47.9%). Regarding the sinus-mucosa relationship, 66.7% of patients had mucosal thickness completely covering the antroliths, and 72.9% had less than one-third of the sinus opacified. Tooth extraction was the most common dental status near the antrolith (45.8%). The shape, size, and volume of antroliths did not affect the surrounding mucosal thickness (p > 0.05), but sinuses containing antroliths had significantly thicker mucosa than those without (p = 0.036).

Conclusions

The findings indicate that although antroliths are relatively rare, predominantly located on the sinus floor and in the molar region, their presence is associated with increased mucosal thickening regardless of their shape, size, or volume. Understanding their radiographic features can aid in differential diagnosis and help anticipate potential complications during surgical interventions.

Trial registration

The trial protocol was retrospectively registered ID NCT06765148 (https://clinicaltrials.gov/); 09/01/2025.

Background

Maxillary antrolith refers to calcific bodies formed within the maxillary sinus. These masses are usually formed by accumulating mineral salts around a central nidus of endogenous origin (such as mucus in the sinus, tooth, or bone fragment) or exogenous origin (foreign objects such as paper, beads, root canal filling materials, vegetable seeds). Although the pathogenesis of maxillary antrolith formation is not fully understood, it is assumed that predisposing factors such as chronic infection, poor sinus drainage, foreign objects entering the sinus, and external trauma to the maxillary sinus play a role [1,2,3].

Antroliths are uncommon, with incidence rates ranging from 0.15 to 8.4% [1, 4,5,6,7,8]. Maxillary antroliths are usually discovered incidentally during radiologic examinations and are usually asymptomatic, although they may enlarge or carry a risk of infection. Possible symptoms include epistaxis, nasal obstruction, facial pain, foul-smelling nasal discharge, cacosmia, anosmia, hyposmia, oroantral fistula, and halitosis. These symptoms can vary depending on the size and location of the antrolith, as well as any complications such as infection or damage to nearby structures. In small asymptomatic antroliths, regular check-ups and/or conservative treatment are considered treatment. Symptomatic and complicated antroliths are usually removed surgically via endoscopic sinus surgery or the Caldwell-Luc approach. However, more comprehensive approaches are used in complex cases such as sinusitis/oroantral fistula formation [8, 9]. It is extremely important to evaluate the radiologic characteristics of antroliths to ensure appropriate treatment and avoid unnecessary treatment.

Antroliths can be observed radiographically as irregular or well-defined radiopaque and more often radiolucent masses of different sizes and shapes within the maxillary sinus. Antroliths, which are usually seen singly, can also be seen in more than one number [1, 5]. Two-dimensional (2D) plain radiographs such as periapical and panoramic radiographs are not sufficient to detect antroliths due to projection effects and superposition disadvantages. Three-dimensional (3D) imaging methods such as computed tomography (CT) and cone beam computed tomography (CBCT) are used to evaluate antroliths. CBCT can also be used in the evaluation of paranasal sinus pathologies with its low radiation dose, submillimetric resolution, and low-cost advantage compared with CT [1, 8,9,10].

Early tooth loss in the posterior maxilla may result in resorption of the bone in the relevant area, and pneumatization of the adjacent sinus into the alveolar crest is also common. For these reasons, CBCT is often used before rehabilitating the relevant area with an implant. Sinus floor elevation (SFE) procedures with a transcrestal or lateral window approach are used for vertical insufficiency of the bone in this region. To perform SFE procedures, it is important to evaluate the health status of the maxillary sinus and exclude possible pathologies [11, 12]. Large maxillary antroliths or those located adjacent to the sinus floor/sinus lateral wall may increase the risk of Schneiderian membrane perforation during SFE procedures [10, 13]. Antroliths may also be confused with other radiopacity pathologies located within the sinus (residual root fragments, osteogenic (osteomas) and odontogenic lesions (cementoma), periapical condensing osteitis, and calcified neoplasm) [14, 15].

The ability to detect and evaluate antroliths in three dimensions is extremely important both in the selection of surgical technique in surgical intervention planning, in determining the prognosis of the intervention, and in the diagnosis of the relevant calcification. Therefore, it is necessary to determine the characteristics of antroliths located in the sinus, such as size/location area, and to distinguish them from possible pathologies. This study aimed to determine the frequency, distribution, location, and volume of maxillary sinus antroliths and the relationship between maxillary sinus antrolith volume and sinus mucosal thickness/maxillary sinus ostium using retrospective CBCT. Also, to evaluate the relationship between the dental treatment status of the teeth adjacent to the maxillary sinus antroliths, and establish whether antroliths detected in CBCT could also be diagnosed in digital panoramic radiography (DPR). This study is the first to compare the detectability of antroliths in both 3D and 2D images while also assessing antroliths in 3D through volume measurements. It addresses gaps in the literature and makes a valuable contribution to the field.

Methods

Selection of the study cohort

This retrospective study was conducted in strict adherence to the relevant ethical principles, including the World Medical Association Declaration of Helsinki of 1964 and subsequent revisions. The study received approval from the Recep Tayyip Erdoğan University Non-Interventional Ethics Committee (2024/299) as retrospective research using CBCT scans previously obtained for the diagnosis or treatment planning of complex oral surgery procedures, such as impacted teeth, skeletal anomalies, or implant surgeries. All patients gave consent for future anonymous use of their radiographs for research purposes.

CBCT images from a total of 1166 patients aged 11–85 years, who presented to the Department of Oral and Maxillofacial Radiology between 2022 and 2024, were evaluated retrospectively.

Patients who underwent DPR and CBCT and also had a maximum of 3 months between the two image recording times were included in the study. All tomographic images that included both maxillary sinuses in the imaging area, where all walls of the maxillary sinuses and the ostium could be evaluated, where the image quality was sufficient, and where there were no artifacts in the evaluation area, were included in the study. Tomographic images that contained pathologies such as cysts/tumors in the maxillary sinuses or adjacent anatomic structures, had insufficient diagnostic quality, history of maxillofacial trauma or surgery, any syndrome/bone-related disease/metabolic disease, and had artifacts that prevented the evaluation of the relevant region were excluded from the study. DPRs with insufficient diagnostic quality or patient position-related artifacts were also excluded.

Imaging protocol and assessment

DPRs were obtained using a Planmeca Promax 2D S2 (Planmeca Oy; Helsinki, Finland) with settings of 66 kVp, 8 mA, and 16.6 s. To ensure an accurate representation of anatomic structures without unwanted distortions, each patient was positioned according to the manufacturer’s instructions and by adjusting the Frankfurt horizontal plane parallel to the ground and the vertical line to the sagittal plane.

CBCT images were obtained using a Newtom VGi-evo (QR Verona, Cefla, Verona, Italy) with parameters of 3 mA, 1.8 s, and 110 kVp with different fields of views of 15 cm × 12 cm, 16 cm × 16–24 cm × 19 cm, 200–300 μm isotropic voxel size, standard resolution mode. Images were evaluated using NewTom’s NNT (NewTom image viewer; NewTom NNT Software version 11.5) at 0.2–0.3 mm slice thickness and 0.2–0.3 mm slice interval. All images were analyzed on a Philips 223 V LED monitor with a resolution of 1920 × 1080 pixels (Philips, Amsterdam, The Netherlands).

Radiographic images were evaluated together by two oral and maxillofacial radiologists with more than 10 years of experience (TEK) and one with more than 1 year of experience (FC), and Excel documentation was created as a result of a single joint decision. When a third opinion was needed on the tomography images, a mutual decision was reached with the guidance of an oral and maxillofacial radiologist (DNG) who had 10 years of experience. The examiners were permitted to use enhancements and orientation tools such as magnification, brightness, and contrast to improve visualization. Images were evaluated on a monitor. No time limit was imposed during the evaluation process of the observers. Two months after the evaluation, 100 randomly selected tomographic images were re-evaluated for investigation of intra-observer agreement.

CBCT images were examined in axial, sagittal, and coronal slices to investigate the presence of antroliths. The age and sex information of the detected cases were recorded. Each sinus cavity exhibiting antroliths was evaluated for distribution and location as follows: unilateral or bilateral, single or multiple, tooth extraction/root canal treatment/residual root fragment/implant/periodontal disease and/or periapical lesion (any dental cause of sinus inflammation), premolar or molar region, sinus floor, lateral wall, or medial wall. The detected antroliths were categorized according to the classification of Cho et al. [11]. In this classification made according to the sizes of antroliths, Punctate = ≤ 3 mm in both height and width, Linear = ≤ 3 mm and more than treble in width, and Amorphous = > 3 mm in both width and height.

Additionally, the locations of the openings of the maxillary sinus ostiums were evaluated, and mucosal thickening, if any, was measured. Mucosal thickness measurements were made on coronal slices using NewTom’s NNT viewer measuring tool. Corresponding to Chen et al., the sinus membrane thickness was measured perpendicular to the bone wall, from the maximum thickest region [4]. Similar to Chen et al.‘s classification of sinus membrane thickness measurements, which used Block and Dostoury’s classification, the mucosal thickness was classified into three subgroups: membrane thickness < 2 mm, 2–5 mm, and > 5 mm [4, 16]. Also, in line with the article by Cho et al., the degree of inflammation in the maxillary sinus was defined as: 1 = mild (less than one-third opacification of the sinus), 2 = moderate (from one-third to two-thirds opacification of the sinus), or 3 = severe (greater than two-thirds opacification of the sinus) [10]. As in the study of Chen et al., the relationship between the antrolith and the sinus membrane was evaluated in sagittal slices. This evaluation was made as follows: Type 1, the sinus membrane encircled less than half the height of the antrolith; Type 2, the sinus membrane encircled more than half the height of the antrolith but did not extend beyond the top of the antrolith; and Type 3, the sinus membrane extended beyond the top of the antrolith [4].

Similar to the study by Chen et al., width (lateral to medial), height (apical to coronal), and length (mesial to distal) measurements were calculated [5]. However, unlike Chen et al. [5], these measurements were performed on paraxial and paracoronal images by readjusting the axes by the antrolith shape (Fig. 1).

Fig. 1

Display of linear measurements on CBCT images; (a) width (lateral to medial) and length (mesial to distal) measurements on the paraxial slice, (b) height (apical to coronal) measurements on the paracoronal slice

Accessory maxillary ostiums (AMOs) were identified as extra openings located on the anterior part of the posterior fontanelle of the lateral nasal wall in coronal slices of the CBCT [17, 18]. At the same time, in cases where antroliths were detected, an evaluation was made for the presence of an accessory ostium.

3D reconstruction and volume measurements of antroliths were performed using the ITK SNAP software (free software under the GNU General Public License developed by the National Institutes of Health, the US National Institute of Biomedical Imaging and Bioenergy needs, the US National Library of Medicine, the Universities of Pennsylvania and North Carolina, and an independent group of developers). In addition, the visibility of antroliths detected on CBCT was also evaluated using panoramic radiographs taken from the patient (Fig. 2). The detectability of antroliths in DPRs was evaluated by observers as detectable, suspicious, and undetectable.

Fig. 2

Antrolith located in the floor of the left maxillary sinus from the same patient; (a) cropped DPR image (b) cropped CBCT image

Statistical analysis

The sample size was determined through a Power analysis. In this analysis, the Type I error rate was set at 5%, the prior power (1 − β) was 80%, and the standardized Cohen’s effect size was d = 0.5. Consequently, a total of 34 antrolith patients were needed for inclusion in the study. The calculations were performed using G*POWER 3.1 (Heinrich-Heine University of Düsseldorf, Germany).

Statistical analyses were performed using the IBM SPSS 8 v. 23 software package (SPSS Inc., Chicago, IL) with a level of significance of 5% (p < 0.05). Descriptive statistics of the measurements were calculated as mean, standard deviation (SD), median, 25th and 75th quartiles, number, and percentage frequencies. The normality of data distribution was evaluated using the Shapiro-Wilk test. The Mann-Whitney U test and the Kruskal-Wallis test were used to compare various groups in terms of numerical structure features, and the post hoc Dunn test was used to determine the groups causing significance. Additionally, relationships between numerical features were evaluated using Spearman’s rank correlation analysis and the independent sample t-test. Relationships between categorical characteristics were assessed using Pearson’s Chi-square test. Cohen kappa was used to evaluate intraobserver agreement.

Results

The weighted κ coefficient was 0.864, and intra-observer reliability was evaluated as good [19].

Two thousand three hundred thirty-two sinuses from 1166 patients were included in the study. Of the participants, 542 (46.2%) were male and 631 (53.8%) were female. The mean age of the participants was 48.5 ± 15.1 years.

Forty-eight antroliths were detected in 41 patients (41/1166 = 3.5%). Of the detected antroliths, 24 were in the right and 24 were in the left sinus. Of the 41 patients with at least one antrolith detected in their sinuses, 16 were male and 25 were female. Bilateral antroliths were detected in three patients. In addition, three other individuals had more than one antrolith (2 in two individuals, 1 in three individuals) in a single maxillary sinus.

There was no significant difference in the mean age between males and females among the 41 patients with antroliths (p = 0.683) (male: 46.44 ± 11.86; female: 45.52 ± 14.80). There was no significant difference in the mean age between the sexes of the 41 people with antroliths (p = 0.683). The average age of patients with antroliths (45.88 ± 13.57) was found to be similar to that of those without (48.59 ± 15.09) (p = 0.257). When the ages were divided into eight classes of 10 and the distribution of antrolith incidence according to age groups was examined, the highest significant antrolith frequency was found in the 81-90-years age group, followed by the 31-40-years age group (Table 1) (p < 0.001). Figure 3 illustrates the distribution of antrolith frequency by age group and sex. No antrolith was detected in the 10–20 and 71–80 age groups. Antroliths were identified in 2 out of 4 patients aged between 81 and 90 years, and both patients were observed in female patients.

Table 1 Distribution of antrolith occurrence according to age groups

Fig. 3

Distribution of antrolith frequency according to age group and gender

It was determined that antroliths were mostly present in the sinus floor (n = 27, 56.3%), followed by the lateral wall (n = 18, 37.5%), and medial wall (n = 3, 6.3%). Of the detected antroliths, six (12.5%) were observed in the premolar region and 42 (87.5%) in the molar region. When evaluated according to Chen et al.‘s classification of the sinus membrane and antrolith relationship [4], the highest rate was observed in Type 3 (66.7%), followed by Type 2 (22.9%), and the lowest was found in Type 1 (10.4%). When the classification made by Cho et al. according to the severity of inflammation in the maxillary sinus in patients with antroliths was evaluated [10], the highest rate was Type 1 (72.9%), followed by Type 2 (14.6%), and the lowest rate was Type 3 (12.5%).

The detected antroliths were classified according to their types, the most common type was amorphous (23/48 = 47.9%), followed by linear (18/48 = 37.5%), and punctate (7/48 = 14.6%). The mean mucosal thicknesses around the linear, punctate, and amorphous antrolith types were measured as 3.06 ± 3.55, 5.76 ± 6.16, and 4.23 ± 4.71 mm, respectively. The mean mucosal thicknesses around the antrolith types were similar (p = 0.515).

The mean thickest mucosal thickness measured in the antrolith region was 4.01 ± 4.54 mm, the mean antrolith volume was 45.44 ± 50.60 mm³, and the mean width, length, and height measurements of the antroliths were 4.08 ± 2.55 mm, 4.17 ± 3.67 mm, and 3.13 ± 2.27 mm, respectively (Table 2). It was found that the change in mucosal thickness caused no significant change in the width, length, and height measurements of the antroliths (Pearson correlation: -0.143, -0.131. and 0.099, respectively).

Table 2 Descriptive values of linear and volumetric measurements of antroliths

After excluding the data of three individuals with bilateral antroliths from the study, the mean maximum mucosal thickness of the sinus with antroliths (9.74 ± 8.56) was compared with the maximum mucosal thickness in healthy sinuses (6.36 ± 6.95), and the mean mucosal thickness in the sinus containing antroliths was found to be significantly greater (p = 0.036).

Antrolith volumes were compared with the three classes defined by Chen et al., and it was seen that there was no significant difference between the classes (p = 0.339). According to Chen et al., the mean mucosal thickness measured in the antrolith region was found to be significantly lower in the Type 1 class than in Types 2 and 3 (p = 0.001) (Table 3).

Table 3 Comparison results according to the three antrolith-sinus relationship classifications defined by Chen et al. in terms of antrolith volume

Similarly, when antrolith volumes were compared with the three classes defined by Cho et al., it was seen that there was no significant difference between the classes (p = 0.359). When the mucosal thickness in the antrolith region was compared between the classes formed according to Cho et al., the average thickness of class 1 was found to be significantly thinner than class 3 (p = 0.046) (Table 4).

Table 4 Comparison results of antrolith volumes according to Cho et al.‘s antrolith-sinus relationship classification

When the relationship between maxillary sinus ostium and mucosal thickness measurement classifications made by Chen et al. was evaluated, it was found that the maxillary sinus of individuals with mucosal thickness less than 5 mm was significantly open, and the maxillary sinus of individuals with mucosal thickness greater than 5 mm was significantly closed (p < 0.001). When the relationship between the presence of accessory maxillary ostium and mucosal thickness was evaluated, it was seen that there was no significant relationship (p = 0.166) (Table 5). The maxillary sinus ostium was found to be open in 44 of the 48 sinuses containing antroliths, and the ostium was closed in the sinuses containing antroliths only four. In addition, accessory maxillary ostium was found in only one sinus with antrolith.

Table 5 Comparison of the relationship between maxillary sinus ostium openness and the presence of accessory maxillary sinus and mucosal thickness measurement

No dental implants located close to the antrolith area. Tooth extraction close to the antrolith area was observed in 22 patients (45.8%), periapical lesion in the tooth in four (8.3%), root remnant in three (6.3%), periodontal problems in two (4.2%), and root canal treatment in three (6.3%).

Of the antroliths identified in CBCT, 29 (60.4%) could not be detected in DPR, 16 (33.33%) could be detected, and the remaining three (6.3%) were identified as suspicious.

Discussion

Maxillary antroliths (antrum cavity within a bone, litho stone), also called rhinoliths, maxillary sinus stones, antral calculi, antral stones, antral rhinoliths, antroliths, and sinoliths, show concentric rings when examined histologically, similar to those found in calculi located in different organs of the body covered by richly vascularized granulation tissue [1]. These rare calcifications have been found to have different frequencies in various imaging methods in the literature. Nass Duce et al. found three antroliths in 1957 (0.15%) patients in their retrospective CT scan study [1], and Aoun and Nasseh found antroliths in three of 500 (0.6%) patients in their retrospective panoramic scan study [14]. In studies using CBCT, Cho et al. detected antroliths in 138 out of 13,946 patients (0.99%) [10], Sanchez-Perez et al. found two out of 160 patients (1.25%) [20], Lana et al. found 16 out of 500 patients (3.2%) [21], Çakır et al. reported 31 out of 621 patients (4.99%) [22], and Rege et al. found 43 (3.2%) out of 1406 sinuses in 703 patients [23]. Betin-Noriega et al. examined CBCT images of 278 patients and detected antroliths in 59 of 556 maxillary sinuses [17]. In their study of CBCT images of 1566 patients, Bayramov et al. stated that 390 patients had soft tissue calcifications and 10 of these were antroliths (10/390, 2.6%) [24].

Imaging methods and the evaluation features of images are very important in the evaluation of calcifications such as antroliths. The reason why Nass Duce et al. [1] detected antroliths in only three of 1957 patients in their CT study may be that they scanned using a slice thickness and interval of 3 mm. 3D imaging with submillimetric resolution and slice thickness, such as CBCT, increases the detectability of antroliths. In this CBCT study, this frequency was found as 3.5%. The reasons why study results show a wide prevalence may be due to differences in assessment/imaging methods or sample sizes. If the evaluation methods are the same, it is conceivable that they may differ depending on factors such as environmental factors, the race of the subjects, or other genetic influences. In their study, Çakır et al. stated that most small-sized antroliths could not be detected in panoramic radiographs but could be detected very clearly with their location in CBCT images, but they did not make a detectability assessment like in our study. They stated that the size of the antroliths and the image quality of the radiographs were important in detectability and diagnosis, but they did not show a threshold on this issue [22]. According to the results of this study, only 33.33% of the antroliths detected in CBCT could be detected in DPR. Therefore, based on the result that only one-third of the antroliths in the sinus could be detected in 2D images, the superiority of CBCT in the evaluation of the relevant region can be mentioned due to the inadequacy of 2D images to diagnose antroliths. As a contribution to the literature on the radiological features of antroliths, this study is the first to evaluate and compare the detectability of 2D and 3D images.

Antroliths are calcifications that can develop around a concentrated mucus or endogenous (bony fragments, blood)/exogenous (dental implant, gutta-percha points) nidus [1, 10]. In their study evaluating antroliths via CBCT, Cho et al. found a root residue in the sinus in one case and a dental implant in the sinus in one case. However, these two exogenous factors were detected far from the antroliths and were not interpreted as nidus [10]. Although studies state that periapical pathologies adjacent to the maxillary sinus may cause inflammatory abnormalities within the sinus [23], there are also papers concluding that there is no relationship between the two conditions [17]. The reason for the differences in these findings may be that the threshold value for inflammatory mucosal thickening is determined differently in each study (there are different lower limits such as 2/3/6 mm) [17, 23].

In their study with CBCT, Chen et al. evaluated the relationship between dental status such as alveolar bone loss, periapical lesion and root canal filling, and the presence of antroliths. No significant relationship was found between alveolar bone loss and periapical lesion conditions and the presence of antroliths, but it was determined that there was a significant relationship between the absence of root canal filling and the presence of antroliths in the teeth adjacent to the maxillary sinus (p < 0.05). In the same study, it was found that there was a significant relationship between the presence of root canal fillings in the teeth adjacent to the maxillary sinus and the absence of antroliths in the maxillary sinus (p < 0.05). This situation has been associated with the healing of apical chronic infections thanks to root canal filling treatment, as well as the thickening of the maxillary sinus membrane and the decrease in the likelihood of antrolith development. Dental findings other than root canal treatment have not been associated with the development of antroliths, so it has been interpreted that antroliths are primarily caused by sinus irritation rather than odontogenic infection [5]. In their study, Chen et al. included patients with antroliths in the maxillary sinus adjacent to edentulous areas, they did not consider tooth extraction as a dental finding, nor did they analyze the relationship between tooth extraction and the presence of antroliths [5]. Nass Duce et al. examined patients with antroliths in their literature review and noted that 16 of 28 patients had a history of tooth extraction (duration ranging from 3 months to 21 years). In the same study, they also presented three patients who they diagnosed, stating that all three had a history of tooth extraction adjacent to the relevant sinus [1].

The reason why tooth extraction history is such a common feature may be apical lesion/ infection/ periodontal abscesses as a factor for the extraction of teeth in the relevant area, which may contribute to the thickening of the sinus mucosa and the development of antroliths. Alternatively, tooth extraction trauma occurring in the bone and local adverse conditions in post-surgical healing may result in the thickening of the adjacent sinus membrane and an increase in the prevalence of antrolith development. However, in another study Chen et al., contra to these studies, it was found that the frequency of antroliths adjacent to dentate areas (60%) was more frequent than sinuses adjacent to edentulous areas (40%). They attributed this to the fact that antrolith formation following tooth loss was not due to sinus pneumatization [4]. Considering the differences in these results, it can be thought that the effect of odontogenic factors on antrolith development may be limited. Among dental conditions, the frequency of tooth extractions close to the antrolith area is higher than other treatments (45.8%). This result may suggest that the odontogenic cause of tooth extraction may have caused inflammation in the adjacent sinus mucosa, paving the way for mucosal thickening and contributing to the development of antroliths. However, the fact that the history of tooth extraction adjacent to antroliths has a rate of 54.2% and the presence of conditions such as periapical lesions, residual roots, periodontal problems, and root canal treatment have rates of less than 9%, also strengthens the possibility that the etiologic factors of antroliths may be endogenous rather than exogenous odontogenic factors.

According to several articles in the literature, no age or sex predilection has been found in terms of the prevalence of antroliths, it can be seen in all age groups [1, 10, 25]. However, in the study conducted by Chen et al., the prevalence of antroliths was found to be higher in women (66.7%) and older people (age > 49 years) [5]. In our study, in line with the literature, sex distributions were found to be close (53.8% female, 46.2% male), and when the incidence was evaluated based on 10-year age groups, it was detected more frequently in the 81-90- and 31-40-years age groups. However, it may have been a coincidence that that two out of four patients aged over 81 years had antroliths and the other two did not. The increase in the probability of antrolith development and therefore detection with age is among the expected results, consistent with the literature, but in the present study, it was determined that the frequency of occurrence was statistically higher in individuals aged 31–40 years rather than in older ages. The reason for this may be that the potential for antrolith development due to exogenic factors in younger age groups is due to increased exposure to changing environmental factors (e.g., climate change, extended pollen season, air pollution) in recent years.

Chen et al. detected most antroliths in the molar region (95.0%), areas adjacent to the sinus floor (77.5%), lateral walls (17.5%), or medial walls (5.0%). Again, in the same study, they stated that the majority of the detected antroliths were unilateral (82.5%, 14 right-side sinus segments and 26 left-side sinus segments) and single-formed (67.5%) [4, 5]. Cho et al. reported no statistically significant differences in the distribution of antroliths by side (61 right/95 left side). In their evaluation according to multiplicity, 76.9% (120/156) of single antroliths were detected [10]. Cho et al. evaluated antroliths according to their shapes and found them to be mostly punctate (53.1%), followed by linear (31.4%), and amorphous (15.5%) [10]. Çakır et al. detected unilateral antroliths in 28 patients and bilateral antroliths in three patients (18 right, 16 left). One of these antroliths was localized on the medial and two were on the lateral wall, but all other cases were found to be located at the base [22]. Again, similar to Çakır et al., in another study conducted in a Turkish subpopulation, antroliths were found to be unilateral, which was statistically significant [24]. In our study, like the literature, antroliths, which were frequently detected in the molar region, sinus floor and unilaterally, showed equal distribution on the right and left. Unlike the study by Cho et al., the most common antrolith form in this study was determined to be the amorphous type, which may be because 71.5% of the antroliths detected by the relevant researchers were smaller than 10 mm² in size.

Antroliths can be of various sizes. Because antroliths are mostly small and grow over time, their shape and size may be affected by the duration of inflammation in the sinus. In the study conducted by Cho et al., it was determined that antroliths had dimensions of 1 to 91 mm² (average 10.2 ± 15.5 mm²), and 75.1% of them were 10 mm² smaller, as measured using the maximum cross-sectional area computed from the coronal slices [10]. Chen et al., in their study evaluating the dimensions of antroliths in reconstructed panoramic images, found the length as 5.6 × 4.4 (1.2–18.1) mm, width as 4.1 × 2.9 (1.1–13.6) mm, and height as 3.5 × 2.1 (0.9–8.7) mm in sagittal slices [4]. In the present study, it was found that the sizes ranged from 0.7 to 19.80 mm in linear dimensions, and from 0.86 to 220.51 mm³ in volumetric dimensions. In our literature review, no study measuring the volume of antroliths was found, and in this respect, our study is important in terms of contributing to the literature. Additionally, according to our results, the degree of sinus inflammation around the antrolith or the severity of inflammation within the sinus itself did not affect the volume of the antrolith. However, it suggests that rather than the mucosal inflammatory response, the nidus of the antrolith itself could have an impact on its volume.

Evaluation of sinus membrane thickness is one of the necessary criteria for physicians planning sinus augmentation. Sinus membrane perforation is the most common complication during augmentation, and clinical analysis shows that there is a correlation between sinus membrane thickness and sinus membrane perforation. Studies also indicate that the perforation rate increases significantly with both an increase in membrane thickness (> 2 mm) and a decrease in membrane thickness (< 1 mm). Thin sinus membranes are carefully evaluated in surgical procedures due to their inadequate mechanical properties such as in resisting elevating forces or grafted bone insertion. A thick sinus membrane may pose difficulties for physicians due to its properties such as tissue change and loss of structure [4, 26, 27]. For these reasons, physicians should preoperatively evaluate sinus membrane thickness and possible accompanying antroliths. It is also extremely important to evaluate antroliths volumetrically to prevent large-sized antroliths from causing mucosal perforation, especially in surgical procedures such as sinus lifting.

Long-term asymptomatic inflammation occurring in the sinus paves the way for the development of antroliths, and the fact that this process is multifactorial makes it difficult to fully explain the mechanism of antrolith development [10]. Although antroliths located in the sinus floor are associated with mild sinus inflammation in the general population, Cho et al. stated that they saw the two largest antroliths in mildly inflamed sinuses. However, the degree of sinus inflammation that may be a factor in the development of antroliths is unknown; therefore, it is debatable whether a relationship between incidentally detected mild sinus inflammation and antrolith size can be interpreted. In the same study, Cho et al. concluded that there was a significant relationship between the presence of multiple antroliths and the degree of sinus inflammation greater than two-thirds opacification. Additionally, amorphous-shaped antroliths were detected relatively more frequently in areas of sinus inflammation that showed opacification of more than one-third of the sinus but found no statistically significant relationship. This result can be interpreted as supporting evidence that the existence of sinus inflammation is one of the factors involved in antrolith development [10]. Chen et al. evaluated the relationship between antroliths and sinus membranes and showed that sinus membranes tended to surround antroliths, resulting in a gradual increase in membrane thickness. In their study, where they classified membrane thicknesses as < 2 mm, 2–5 mm, and > 5 mm, a statistically significant difference was observed in the proportions of sinuses with and without antroliths in the sinuses with a membrane thickness of < 2 mm (12.5%and 46.6%) and those with a membrane thickness of 2–5 mm (52.5% and 29.6%). For sinuses with membrane thickness > 5 mm, the difference in rates was not statistically significant, but the rate with antroliths (35%) was higher than the rate without antroliths (23.7%) [4]. In the present study, in accordance with the literature, the mean sinus mucosa thickness was found to be statistically greater in sinuses containing antroliths than in sinuses without antroliths. In antrolith-containing sinuses, according to the Chen et al. classification, mucosal thickness more frequently enveloped the antrolith (66.66%), and according to the Cho et al. classification, antrolith-containing sinuses more commonly exhibited less than one-third sinus opacification (72.91%). According to our study results, an increase in mucosal inflammation can be considered one of the factors that predispose to the formation of antroliths; however, it is not associated with the overall severity of inflammation in the sinus. Although antroliths are usually asymptomatic, if there is an increase in mucosal thickness and accompanying inflammation, the clinical approach (e.g., follow-up/medical treatment/surgical approach) may change. Therefore, mucosal changes in patients with antroliths should be carefully evaluated and treatment decisions should be made considering the symptoms and the general clinical condition of the patient.

The maxillary sinus ostium plays an important role in the drainage of seromucous secretions in the sinus into the nasal cavity as well as aeration of the sinus. When it is blocked, the amount of oxygen required to maintain the metabolic activity of the sinus mucosa decreases. As a result, the necessary environment for bacterial proliferation develops with the increase of anaerobic reactions and may cause mucosal thickening [28, 29]. In support of this, significance was found in studies evaluating the relationship between the frequency of ostium obstruction and mucosal thickening [29,30,31]. It has also been reported that mucosal thickening may be a factor in the development of antroliths [10], but contrarily, there is no significant relationship between the presence of these two conditions [17]. Maxillary sinus ostium obstruction is also among the causes of mucosal thickening and may indirectly cause antrolith development. Çakır et al. found the maxillary sinus ostium to be closed in 17.64% of patients with antroliths, but they found no statistically significant relationship between the presence of antroliths and maxillary ostium openness [22]. According to the results of our study, only 8.3% (4/48) of the sinuses containing antroliths had a closed ostium. However, in patient groups with mucosal thickness greater than 5 mm, a significant association with closed maxillary ostium was observed. Although the presence of an antrolith did not directly correlate with a closed ostium, the increase in mucosal inflammation might contribute to the closure of the ostium, or, conversely, a closed ostium could lead to mucosal inflammation, both of which could be considered predisposing factors for antrolith development. Additionally, because the calcification of the antrolith occurs over a long period, the time of antrolith detection may not coincide with the time when the ostium was closed.

Accessory maxillary ostium (AMO) is an anatomic variant of the maxillary sinus that can vary in size, location, and form. It is seen in 30% of patients with chronic maxillary sinusitis and 10–20% healthy sinuses. AMO may cause decreased mucociliary activity and consequently blockage of seromucous glands in the sinus. However, whether maxillary sinusitis contributes to the development of AMO or maxillary sinusitis develops due to AMO has not been fully elucidated [32]. Genç et al. stated that AMO developed after maxillary sinusitis [33]. Zinreich also reported that AMO was more common in individuals with maxillary sinusitis [34]. Matthews and Burke also stated that maxillary sinusitis developed due to mucus secretion directed from the natural ostium to the nasal cavity reentering the sinus via AMO and that it was an important factor in the pathogenesis of sinusitis [35]. Yenigün et al. supported this information and found that the frequency of mucosal thickening and maxillary sinusitis was approximately twice as high in patients with AMO [32]. However, some studies obtained contradictory results. For example, Noriega et al. evaluated the relationship between AMO and thickening of the maxillary sinus mucosa and found no statistically significant relationship [17]. In our study, no relationship was found between the presence of AMO and mucosal thickness, and AMO was found only in a single sinus with antrolith. Therefore, it was evaluated as a factor whose effect on the development of antrolith was difficult to say.

One of the limitations of the study is that the difficulties that may occur due to antroliths in maxillary sinus surgeries could not be evaluated. The lack of information about the development time of inflammation in the sinus is also a limitation. Future studies should be planned multicentrically with larger patient numbers to investigate the possible causative agents of antroliths and overcome the limitations of this study. Although antroliths are mostly asymptomatic, deepening the anamnesis of patients in terms of the symptoms of detected related to antroliths in future studies may contribute to the literature.

Conclusion

This study demonstrates that maxillary sinus antroliths, though relatively uncommon (3.5% prevalence), are more frequently observed in specific age groups (81–90 and 31–40 years) and predominantly located on the sinus floor and in the molar region. Their presence is significantly associated with increased mucosal thickening, regardless of their shape, size, or volume. The fact that antroliths are mostly asymptomatic and have limited detectability in DPRs, which are widely used in dental treatment procedures, may cause difficulties in their clinical diagnosis. Recognizing the radiographic features of antroliths is essential for accurate diagnosis, differentiation from other maxillary sinus pathologies, and anticipating potential surgical complications before implant surgery, especially procedures that include surgical steps such as sinus lifting.