{'fraction_non_alphanumeric': 0.0316834574390422, 'fraction_numerical': 0.017958826106000875, 'mean_word_length': 4.894578313253012, 'pattern_counts': {'":': 0, '<': 1, '<?xml version=': 0, '>': 2, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
A computed tomography-based morphometric study of the styloid process

BACKGROUND
The styloid process (SP) refers to a cylindrical piece projecting from the inferior of the temporal bone, situated anterior to the stylomastoid foramen. It is an anatomic formation close to major vessels and nerves, and its excessive elongation results in pathologies leading to anatomical disorders, such as Eagle's syndrome. Several studies have been conducted on SP in relation to its close proximity to vessels and nerves, but there is no study that reveals its distance to important anatomical formations, such as the internal auditory meatus (IAM), carotid canal (CC), cochlea, tegmen tympani (TT) and tragus. In the current study, we aimed to investigate the incidence of Eagle's syndrome based on morphometric measurements of SP.


MATERIALS AND METHODS
The patient files archived in the Radiology Department of Adiyaman University Training and Research Hospital were retrospectively examined. The study was carried out on the data of patients for whom specialist radiologists found no pathology findings on the CT images. A total of 77 individuals (36 females and 41 males) aged 22 to 54 years were included in the study. The length of SP and its distances to IAM, cochlea, CC, TT and tragus were obtained using CT radiological measurements.


RESULTS
When the individual measurements performed on CT images were evaluated in men and women, no significant difference was found concerning the distance between SP and various anatomic structures in close proximity to SP (p>0.05). However, there was a statistically significant difference between the genders in length of the right SP (p=0.003) and left SP (p=0.006).


CONCLUSIONS
This anthropometric study revealed the standard morphometric measurements of SP. We believe that the data obtained will help clinicians to identify and diagnose pathologies more easily.


INTRODUCTION
The temporal bone is a complex structure located in the temporal region, including organs related to hearing and balance. It consists of three parts: petromastoid, squamous, and tympanic (1). The styloid process (SP) is a cylindrical piece projecting from the inferior surface of the petros part of the temporal bone, situated anterior to the stylomastoid foramen between the internal and external carotid arteries and the pharyngeal wall (2). Being located in the temporal bone, SP is a clinically important anatomical entity due to pathologies caused by changes in its length (3).
Excessive elongation of this structure, which has close proximity to important vessels and nerves, results in pathologies that cause anatomical disorders (4). The normal length between the SP base and the apex is 25 mm, and a measurement of 30 mm or greater is considered to indicate elongation of SP and called Eagle's syndrome, which causes pain, dysphagia, glossopharyngeal and neurological symptoms (5,6). In clinical practice, in the evaluation of pathological changes related to diseases, it is necessary to have knowledge of the normal anatomy of the structure in question and standardize morphometric measurements of its distance to the surrounding formations.
Several studies have been conducted on SP focusing on its close proximity to the vessels and nerves, but to the best of our knowledge, there is no study revealing its distance to important anatomical formations, such as the internal auditory meatus (IAM), carotid canal (CC), cochlea, tegmen tympani (TT), and tragus (7)(8)(9). Such measurements are important for determining normal values in clinical cases characterized by vertigo, tinnitus, chewing problems, and pain.
In the current study, morphometric measurements of SP were undertaken to clarify the mean SP length, and the distance of SP to neighboring anatomical structures, as well as their relationship were determined. The data obtained from the study is expected to assist physicians in diagnosing cases presenting with symptoms disrupting their quality of life, such as vertigo, tinnitus, chewing problems, and pain.

MATERIALS AND METHOD
In this study, the patient files obtained from the archives of the Radiology Department of Adıyaman University Training and Research Hospital were retrospectively examined. A total of 77 patients, 36 women and 41 men (age range: 22-54 years), who underwent computed tomography (CT) of the temporal bone between June 2018 and January 2019 were included in the study. The radiological images were re-evaluated by a radiologist with more than 10 years of experience. The cases with poor CT image quality or a history of head and neck surgery, as well as those that underwent temporal bone CT for trauma and tumor were excluded. Incidents that do not concern temporal bone structures, such as sinusitis and adenoid hypertrophy were disregarded ( Figure 1).

CT Protocol and Imaging Analysis
In all cases, CT was performed using a Toshiba Aquilion 64 system (ToshibaMedical, Tochigi, Japan). The CT scans were continuously obtained in the axial plane, parallel to the infraorbitomeatal line, covering the area from the arcuate protrusion in the upper part to the mastoid apex in the lower part (FOV: 22 cm, thickness: 0.5 mm, kV: 120, mAs: 200, effective mAs: 150). The radiological images were evaluated in the coronal plane using a dedicated workstation. Multi-planar and 3D images were used where necessary ( Figure 2). The measurements were undertaken and recorded in millimeters.
The root length of SP was accepted as the tympanic part of the temporal bone.
The mediolateral line passing through the lower border of the SP root in the coronal plane, parallel to the scanning plane, was taken as the reference point. Performing measurements on this reference line, the distances of SP to IAM, CC, cochlea, TT and tragus were noted. In addition, the total length of SP measured on 3D and/or maximum intensity projection images was recorded (Figures 3-10).

Statistical Analysis
Statistical analyses were performed using SPSS 15.0 program after transferring the data obtained from radiological images to a computer environment. The suitability of the data for normal distribution was evaluated by the single-sample Kolmogorov-Smirnov test. Levene statistics were used for the homogeneity analysis of group variances. The independent samples t-test was conducted to determine the differences between male and female biometric measurements, and the paired-samples t-test was utilized to determine the differences between the left and right measurements of men and women. The results were obtained as mean ± standard deviation (SD). The significance level was accepted as p < 0.05.

RESULTS
The mean age was 39.00 ± 10.76 years for 36 female participants and 34.85 ± 8.19 years for 41 male participants. The mean lengths of the right and left SP were found to be 30.11 mm and 29.12 mm, respectively in women, and 30.30 mm and 29.36 mm, respectively in men. SP was measured more than 30 mm in seven of the women, bilateral in five and unilateral in two (1 right and 1 left). In males, SP was measured to be longer than 30 mm reference value in a total of nine cases, seven of whom were bilateral and two were unilateral (right side). Eagle syndrome was reported to be 19.4 and 21.9% in women and men, respectively. When all women and men were evaluated together, the prevalence of eagle syndrome was 20.7%.
In CT measurements performed individually for the women and men, the lengths of the right and left SP and the distance of SP to the surrounding tissues were determined (Figures 3-10). When the measurements were statistically evaluated, there was no difference within the groups in the gender-based comparison of the distance between SP and various neighboring anatomical formations (p > 0.05) ( Table 1).
However, according to the gender-based intergroup comparisons, there were statistically significant differences in the root length of the right (p = 0.003) and left (p = 0.006) SP (Table 2).
There was a significant difference between men and women concerning the distance of SP to the right IAM (p = 0.027), but no significant difference was found in the distance of SP to the left IAM (Table 2). According to the gender-based intergroup comparisons, the distances of SP to the right (p = 0.043) and left (p = 0.021) cochleae were significant. Similarly, the distances of SP to the right (p = 0.001) and left (p = 0.058) CC provided significant results ( Table 2).

DISCUSSION
Styloid process, which is part of the temporal bone, is an important anatomical formation that provides attachment points for muscles and ligaments (3). SP is important for both medical doctors and dentists due to its proximity to many important anatomical structures in this part of the body.
In studies investigating SP length, the normal length of SP was reported as 25 to 30 mm by Eagle (10), less than 30 mm by Kaufman et al. (11), and 15.2 mm by Moffat et al. (12). When the current literature is examined, it is observed that the length of SP varies from 15 to 47 mm, and values above 30 mm are considered to indicate elongation of SP, which is known as Eagle's syndrome (9). According to our study data, the mean SP length was 29 mm in women and it approached 30 mm in men. The length of SP can vary greatly with differences being observed even in the same individual between the right and left sides.
In the literature, elongated SP (Eagle syndrome) frequency is highly variable and reported between 1.4 and 83.6%; however, radiographic incidence is between 2 and 32% (13). Several studies investigating the prevalence of Eagle syndrome in Turkish population have been reported between 1.1 and 7.7% (14). In this study, this rate has been found higher (20.7%).
Studies present different results concerning the relationship between the SP length and gender (15)(16)(17)(18). For example, Nalçacı et al. found no significant difference between the SP length and gender, but according to our measurements, the gender-based differences in the right and left SP lengths were significant (19). We believe that the significantly longer SP in males is due to the anatomical variations related to gender. In addition, the distances of SP to some of the neighboring structures were also observed to significantly differ between the right-and left-side measurements. This suggests that in addition to the gender-based differences in anatomical structures, it is possible to observe variations in the different anatomical regions of the same person. Therefore, we consider that gender-based and right-left differences should be considered in clinical approaches.
The distance between SP and the cochlea was 16 mm in females and males, while the SP-CC distance significantly differed between genders, being measured as 15 mm and 16 mm, respectively. The mean SP-TT distance was 17 mm, and the SP-tragus distance ranged from 34 to 36 mm. With these measurements, the distances of SP to the neighboring structures were determined as reference values for the Turkish population.
Our review of the literature did not show any such radiological data. Thus, we consider this as a fundamental study that radiologically reveals the morphometry of SP, a structure that causes various pathologies in medicine and dentistry, in relation to its neighboring structures.
We believe that SP-related factors can also cause pathologies characterized by vertigo, tinnitus, chewing problems, and pain. When the literature is examined in detail, regional pain due to calcification of the stylohyoid ligament is seen (23). Cranial nerve and carotid artery compression due to anatomical changes in this region are known as causes of vertigo (24-26). The SP-CC distance obtained from this study and gender-based measurements provide normal values that can be used as reference in identifying possible pathologies. It has previously been reported that SP-related differentiations can lead to the compression of the cranial nerve, resulting in facial pain, dysphagia, foreign body sensation, hypersalivation, tinnitus, and otalgia during head rotation (27).
Diagnosis and treatment are of great importance in the elimination of abovementioned complaints that disrupt the ergonomics of life. We believe that the normal values of SP in different populations population should be clarified in order to eliminate SP-related anatomical defects. This will make it easier to identify pathologies and prevent possible defects through preoperative planning and various medical treatments.
Knowing the length of the SP and its distance to adjacent anatomic structures may shed light on prior planning in surgical procedures of these locations (such as head and neck and dental surgery), avoiding potential complications such as carotid artery injuries. We also hope that the radiological demonstration of these complex anatomical structures in the neighborhood of SP will make it easier for anatomy students to understand. This study has certain limitations. The first one concerns the retrospective design and it also includes the small sample size. The second one is that clinical and laboratory data leading to the consideration that cases were healthy was only accessed through the archives.

CONCLUSIONS
In this study, the relationship of certain parts of the temporal bone with SP and standard morphometric measurements of SP were determined based on CT data.
Knowing the radiological measurements of SP and its relationship with other formations on the temporal bone can be a radiological and anatomical guide for the diagnosis or monitoring of health problems that impair the quality of life, such as tinnitus, vertigo, chewing problems, and especially Eagle's syndrome.