EVALUATION OF STYLOHYOID LIGAMENT CALCIFICATIONS IN THE CENTRAL ANATOLIAN REGION

ABSTRACT


INTRODUCTION
The term styloid process (SP) comes from the Greek vocable "stylos" meaning a column. As can be understood from this definition, SP, which has a thin and cylindrical structure, is anatomically located between the internal and external carotid artery, in the anterior part of the temporal bone, anterior to the stylomastoid foramen 1 . The average length of SP reported as "normal" in adults is 25 mm 2 . For SP sizes above the normal value, the definition of the elongated styloid process (ESP) is used 3 . In 1937 the ESP designation was first defined by Dr. Watt W. Eagle. Eagle syndrome, which is characterized by symptoms such as head, and neck aches, difficulty in swallowing, and foreign body sensation in the throat associated with ESP, is also named after Dr. Watt W. Eagle [4][5][6] .
ESP is usually asymptomatic, but approximately 4% of the patients may have symptoms such as vertigo, earache, tinnitus, trismus, dysphagia, and facial pain.
Depending on size, shape, and location, ESP may cause paralysis by compressing the carotid artery 7 . The differential diagnosis of ESP includes many diseases with similar symptoms such as cervical myofascial pain syndrome, glossopharyngeal neuralgia, migraine, trigeminal neuralgia, otitis media, temporomandibular joint pain, tonsilloliths, and atherosclerosis. Therefore, clinicians should know the normal anatomy and abnormalities of SP 8,9 . There are different theories about the etiology of ESP based on anatomical, embryological, and physiological origins, but the mechanism of ESP formation is still not fully understood 2 .
Different imaging methods such as panoramic radiography, lateral head radiography, computed tomography (CT), and cone beam computed tomography (CBCT) are utilized in the diagnosis of ESP. 3 Among these methods, panoramic radiography is the preferred method in the diagnosis of ESP due to its widespread use, low cost, low radiation dose, and showing the entire maxillofacial complex in a single image, and ESP is usually detected incidentally on routine panoramic radiographs 2,10 .
This study was aimed to evaluate the prevalence of ESP on digital panoramic images in a selected patient group and to evaluate the distribution of the SP length of the patients according to age, gender, and systemic diseases.

MATERIALS AND METHODS
The approval for the study was obtained from the Necmettin Erbakan University Ethics Committee with the number 2023/262. Panoramic images of 1000 patients who applied to Necmettin Erbakan University, Faculty of Dentistry, Department of Dentomaxillofacial Radiology between January 2020 and January 2022 were obtained from the database, and the study group was formed. Panoramic images were obtained by the same technician in the Morita Veraviewepocs 2D panoramic device (J Morita MFG Corp., Kyoto, Japan) according to the protocol (70 kVp, 5mA, 8 s) recommended by the manufacturer. Right and left side SP lengths were measured on each panoramic image. Measurements were made on the images using the length measurement tool available in the current software (Turcasoft). This program is a software that allows length, area, and angle measurements on panoramic images in the digital environment, as well as making sharpness and density adjustments and storing images. In the measurement of SP length, based on the method of İlgüy et al. 7 , the point where the SP first splits from the temporal bone and its extreme point were determined as reference points Figure 1.
The distance between these points was measured with the ruler tool in the Turcasoft program and the length value was calculated as "mm". Measurements greater than 30 mm in length were considered ESP. The actual sizes in measurements were calculated using a magnification factor of 1.3. O'Carrol and Jackson 11 classification was used to evaluate the types of styloid ligament calcification Figure 2. All measurements were performed by a radiologist on a 27-inch flat panel color screen (Dell U2711HTM) with a resolution of 2,560x1,600 pixels, under appropriate lighting conditions. Measurements on 100 panoramic images of randomly selected patients were repeated 3 weeks later to assess intra-observer agreement.

Figure 2. Examples of SP types according to the O'carrol and Jackson classification
The obtained data were transferred to the SPSS 21.0 (IBM Corp., Armonk, NY, USA) program. Descriptive statistics (mean, standard deviation) were determined for all factors in the study. Paired-sample T-test was used to compare right and left measurements. Independent sample T-test and One-Way ANOVA test were performed to evaluate the differences in the measurements according to gender and age groups. The correlation of the measurements with each other and with the age groups was examined with the Pearson correlation test. Styloid types and age groups, gender, and systemic disease relationship were evaluated by Chi-square test, and a p<0.05 significance level was accepted. Intra-observer agreement for length measurements was assessed by the Cronbach's-alpha test.

RESULTS
Right and left SP lengths were measured on 1000 panoramic images. Intraobserver agreement was found to be quite high (0.924) in the evaluation of the measurements. A total of 1000 (40±15.24) patients [531 (39.97±15.1) females and 469 (41.88±15.47) males] between the ages of 18-95 were evaluated Table 1. SP was found to be greater than 30 mm in a total of 304 (30.4%) patients. It was observed that 291 (95.7%) ESPs were bilateral in these patients. It was determined that 169 of the patients with ESP were female (55.6%) and 135 were male (44.4%). The mean length of the right SP was 28.78±7.49 mm, and the left average was 29.12±7.71 mm. As a result of the statistical analysis, it was observed that there was no statistically significant difference between the right and left measurements Table 2.
There was no statistically significant difference between the right and left SP lengths for the genders. In women, the mean right SP was 28.59±7.49 mm, left SP was measured as 28.94±8.18 mm. In men, the mean right SP was 29.01±7.89 mm and the left SP was measured as 29.35±7.28 mm Table 3. Although there was no significant difference between left and right SP lengths, it was observed that the left SP was longer than the right SP. The shortest right SP was 10 mm, while the left SP is the shortest 10.9 mm. It was determined that the longest right SP was 56.72 mm, and the left SP was 68.91 the longest.
There was no significant difference between right and left SP lengths for age groups Table 4. SP measurements were highest in the 61+ age group and lowest in the 41-60 age group for both right and left measurements. It was found that right and left SP measurements correlated with each other, but not with age groups Table 5. In the dispersion of SP types according to their age, it was established that the most common Type 1 was in the 18-40 age range, while the least common Type 4 was in patients aged 61 and over. In total, the most common type was Type 1, and the least common was Type 4 Table 6. No statistically significant relationship was found between SP types and both gender and systemic diseases

DISCUSSION
In this study, SP length measurements were evaluated with panoramic radiography due to its widespread use, diagnostic performance, low cost, and low radiation dose 12 . Conebeam Computed Tomography (CBCT) is an additional and effective method to accurately diagnose the length, angle, and structure of the styloid chain complex. However, it is not as common as panoramic imaging because it is used in a limited number of patients and cases. Apart from these, other imaging methods used for the evaluation of the styloid process are postero-anterior skull view, Towne's view X-ray, lateral cephalogram, lateral-oblique mandible view, and computed tomography 3,4 .
The prevalence of ESP varies widely in different populations. Studies have reported that the prevalence of ESP varies between 0.4% and 83.6% 13,14 . In this study, the prevalence of ESP was found to be 30.4% in the selected patient group. It is reported that this difference between studies is due to differences in measurement and evaluation procedures and differences between races 15 . The prevalence of ESP in studies performed with panoramic radiography varies between 4% and 28% 7,16 . Since the results of our study are in this range, they agree with similar studies.
The use of panoramic radiography in the diagnosis of ESP has been suggested by many researchers 7,16,17 . This is because it is a simple technique and the entire maxillofacial complex is visualized on a single film 18,19 . However, it is necessary to be careful in the acquisition and analysis of images and to minimize the distortion that occurs in panoramic radiography by using the appropriate method. It is also important to calculate the factor of magnification in the image 14 . If these criteria are not met, different statistical results may occur in millimetric measurements. In this study, these criteria were carefully evaluated, and panoramic images with low image quality and distortion were not included in the study. In addition, the measurements were carried out by calculating the magnification factor.
Different techniques have been used in the literature for the measurement of SP length. In the measurement of SP length, Jung et al. 20 used the distance between the tympanic plain of the temporal bone and the tip of the SP. Guimaraes et al. 21 on the other hand, the lower border of the ear cartilage was taken as a reference, and the values measured 1 cm and above from this border were accepted as ESP 7 . In this study, the method of İlgüy et al. 7 was used and values measured at 30 mm and above were determined as ESP.
ESP can be seen unilaterally or bilaterally on panoramic radiographs. In the studies of Guimaraes et al. and Lins et al. bilateral ESP was detected in approximately 84% of the patients 14,21 . In the study of Andrade et al., the incidence of bilateral ESP was found to be 54% 22 . In this study, bilateral ESP was found in 96% of the patients with ESP. The reason for this difference may be due to the racial differences between the study groups. Altındağ et al. evaluated SP according to the Jankowski classification and found it to be bilateral at a rate of 80.4%. Although it was studied in the same population, this difference between the results may be due to the use of different study groups and different classifications.
The average reported length of SP in adults is 20-30 mm 2,12 . Eagle reported that the normal length of SP was approximately 25 mm. 23 Natsis et al. 24 in their study on dry skulls, found the mean value of SP length to be 25.2 mm for right-sided measurements and 24.7 mm for left-sided measurements. In this study, the mean length of the right SP was 28.78 mm, and the left SP length was found to be 29.12 mm on average, which was slightly higher.
In the literature, when the prevalence of ESP is evaluated according to gender, it is seen that there are different results. Lins et al. 14 , Vieira et al. 15 , and Chabikuli and Noffke 25 reported that the prevalence of ESP was higher in women than in men, while More et al. 16 , Bagga et al. 26 , Shaik et al. 27 , and more reported that the prevalence of ESP was higher in men. In this study, the prevalence of ESP was found to be higher in women (56.6%). There was no significant difference in the mean length of SP in men and women. In many studies, it has been reported that gender does not have a significant effect on SP length 3,24,28,29 . In the study by Nalçacı and Mısırlıoğlu 18 in which they evaluated SP in individuals over 55 years of age, no significant relationship was observed between gender and SP length. However, it was determined that the SP length in men inclined to be longer than in women. Similar results were found in this study.
Jung et al. 20 suggested that genders and age groups were equally distributed in their study, and therefore the results of their study were more accurate than other studies. In their study, they observed that the length of SP was bigger in men, and the length of SP increased with age. In the study of Mısırlıoğlu et al. 18 27 , Sokler and Sandev 30 , and Anbiaee and Javadzadeh 31 argued that SP length correlated with age. Natsis et al. 24 , Öztunç et al. 32 , and Gökçe et al. 33 revealed that there was no correlation between age and SP length. In this study, no significant difference was found between age groups in SP measurements, and no correlation was found between age and SP length.

CONCLUSION
As a result of the study conducted on a limited number of patients, the prevalence of ESP in panoramic radiography was found to be 30.4%. Although the prevalance of ESP was higher in women, SP length measurements did not show significant differences between genders and age groups on average. In addition, there was no significant correlation between SP length and age. To view the SP, panoramic radiography is an easy-to-access and useful method. However, examining it with advanced imaging techniques will reveal more accurate results.

ACKNOWLEDGMENT
Thanks to Dr. Ömer Altındağ from Science and Letters, Statistics and Computer Sciences Department, Bilecik Şeyh Edebali University for the help and guidance to the statistical analysis throughout forming this paper.