Introduction

The atlas, or C1 vertebra, situated at the top of the spine (Buyuk et al. 2017), is distinguished by its unique characteristics, including the absence of a vertebral body, a special articulation with the cranium on its upper side, and being mostly cartilaginous at birth, with variations, such as ponticulus posticus (PP) (Rao et al. 2013). Each superior articular process of the atlas features a sulcus arteriae vertebralis (Krishnamurthy et al. 2007), guiding the vertebral artery and the first spinal nerve. This sulcus, located on the posterolateral margin of the posterior arch, can sometimes form a bony bridge known as PP in various manifestations, potentially causing symptoms, such as vertigo, headache, and neck pain due to vertebral artery and nerve root encasement (Krishnamurthy et al. 2007; Chen et al. 2015; Saleh et al. 2018; Pękala et al. 2017; Putrino et al. 2018).

Situated behind the anterior base of the skull, the sellar region occupies a central position within the skull base (Go and Rajamohan 2017). The sella turcica (ST), located on the intracranial surface of the sphenoid body in the middle of the cranial area (Magat and Sener 2018), is comprised of four components: the tuberculum sella, the pituitary fossa, and the anterior and posterior clinoid processes (Yasa et al. 2017a). This intricate structure has significant implications for adjacent anatomical features such as the pituitary gland and cranial nerves (Magat and Sener 2018). The pituitary fossa, a key depression within the ST, serves as the site for the pituitary gland. Notably, individual differences in the ST's morphology are critical for identifying potential abnormalities in this region (Magat and Sener 2018; Valizadeh et al. 2015).

The stylohyoid complex is made up of three key components: the styloid process (SP), the stylohyoid ligament, and the lesser horn of the hyoid bone. These structures all emerge from the second pharyngeal arch, highlighting their shared embryological origin (Krennmair and Piehslinger 2003). Situated near the stylomastoid foramen, the SP is a slender bone that links to the hyoid bone and underpins muscles and ligaments crucial for mastication and swallowing (Bruno et al. 2017). A normal SP length ranges from 20 to 30 mm, and when it exceeds 30 mm, it is termed an elongated styloid process (SPE) (Bruno et al. 2017; Gokce et al. 2008a). SPE can manifest with symptoms such as neck and cervicofacial pain, known as Eagle’s syndrome, necessitating surgical intervention (Omami 2018) due to compression of nearby neural and vascular structures (Gokce et al. 2008b).

To assess the prevalence of PP and the types of ST and stylohyoid complex calcifications, methods such as plain radiographs and dried skull examinations have been used. However, cone beam computed tomography (CBCT), with its ability to provide three-dimensional imaging, offers a more detailed and accurate analysis than these traditional methods. CBCT is advantageous due to its high-quality imaging similar to computed tomography (CT), but with more cost-effective equipment, reduced examination time, and significantly lower radiation exposure (Chen et al. 2015; Yasa et al. 2017a).

This retrospective investigation aimed to ascertain the frequency of PP and stylohyoid ligament calcifications, as well as to contrast the variations in ST morphology within the Turkish population, utilizing CBCT for analysis.

Materials and methods

The research was rigorously performed in alignment with the ethical standards delineated in the Declaration of Helsinki, and received the requisite ethical approval from the Committee for the Evaluation of Scientific Research Ethics. The study involved a retrospective analysis of CBCT scans from patients who visited the Dentomaxillofacial Radiology Department at the Faculty of Dentistry, Near East University, for various diagnostic purposes. The images used in this study were meticulously examined using the NewTom 3G system (Quantitative Radiology s.r.l., Verona, Italy).

Evaluation of the images

Only diagnostically acceptable images were included in the study. The CBCT images were analyzed in an NNT viewer; which is a simple version of NNT software of the CBCT (NewTom 3G, QR, Verona, Italy) machine in a Dell Presicion T5400 workstation (Dell, Round Rock, TX, USA), using a 32-in. Dell LCD screen with a resolution of 1280 × 1024 pixels in a darkroom. The contrast and brightness of the images were adjusted using the image processing tool in software to ensure optimal visualization.

The CBCT images were then converted into three-dimensional models for a thorough examination. The focus was on identifying PP, various forms of the ST, and calcifications in the styloid ligament. This evaluation was conducted independently by three professionals: a dentomaxillofacial radiologist with 8 years of experience and two research assistants each with 2 years of experience. To minimize any potential discrepancies, a sample of 96 images was randomly chosen and reassessed by these observers 1 month after the first assessment. The findings reveal a noteworthy concordance between the repeated measurements conducted by the observers 1 month apart and the initial measurements. Notably, intra-class correlation coefficient (ICC) values exceeding 0.9 signify a robust degree of agreement (p < 0.05).

Evaluation of the ponticulus posticus

The preliminary assessment of PP in this study was conducted collaboratively by three experienced observers, both well-versed in evaluating volumetric data from CBCT scans. This team approach ensured a consensus in the initial findings. In addition, the study delved into the prevalence of PP, taking into account gender differences. The findings were categorized based on whether the PP was fully formed (complete) or only partially developed (partial) (Fig. 1).

Fig. 1
figure 1

Anatomical variations of ponticulus posticus: a absence of PP, b partial PP, c complete PP

Full size image

Evaluation of stylohyoid ligament calcification

For the assessment of the elongated stylohyoid ligament, axial images were primarily utilized. In addition, the evaluation of the SP incorporated images from axial, coronal, and sagittal planes. The clinicians meticulously examined and documented the configuration of the stylohyoid chain complex on both sides.

The study also focused on the prevalence of stylohyoid ligament calcification, categorizing it based on MacDonald-Jankowski’s (2001) classification. This research categorized the SP based on the following criteria: it was deemed 'normal' if its extension did not exceed the level of the mandibular foramen (patterns a–d). It was considered 'elongated' if it surpassed the mandibular foramen level and seamlessly integrated with the skull base (pattern e). Conversely, it was termed 'calcified' if it extended beyond the mandibular foramen without appearing to directly connect with the skull base (patterns f–k) (Fig. 2).

Fig. 2
figure 2

Stylohyoid complex exhibits 12 unique patterns of calcification; a exclusive to the tympanohyal region (Region 1); b confined to the stylohyal region (Region 2); c independent calcifications in both the tympanohyal and stylohyal regions (Regions 1 and 2); d uninterrupted calcification spanning the tympanohyal and stylohyal regions (Regions 1 and 2); e continuous calcification through the tympanohyal, stylohyal, and a third region; f distinct calcifications in the tympanohyal, stylohyal, and a third region; g continuous calcification in the tympanohyal and stylohyal regions, with a separate third region; h independent calcification in the stylohyal and a third region; i uninterrupted calcification in the stylohyal and a third region, with the tympanohyal region separate; j calcification solely in a third region; k continuous calcification in a third region and a fourth region, potentially including calcification in one additional region; (l) no visible styloid process

Full size image

Evaluation of sella turcica

The classification of the ST shapes in this study was based on the criteria established by Axelsson et al. (2004). This classification divided the ST into six distinct groups. The first group, labeled as 'normal ST' (a), represents the standard morphology. The other five groups encompass various morphological variations of the ST: 'oblique anterior wall' (b), which indicates a slanted front wall; 'significantly reduced depth of ST' (c), where the ST has a much shallower depression than is usually observed; 'ST bridging' (d), denoting the presence of a bony bridge within the sella; 'irregularity in the posterior part of the dorsum sellae' (e), referring to unevenness or deviations in the back part of the dorsum sellae; and lastly, 'pyramidal shape of the dorsum sellae' (f), where the dorsum sellae exhibits a pyramid-like form (Fig. 3).

Fig. 3
figure 3

Classification of sella turcica morphology includes six distinct types: a normal sella turcica, characterized by its typical anatomical structure; b oblique anterior wall, where the front boundary slopes at an angle; c significantly reduced depth of sella turcica; d sella turcica bridging, which involves the formation of a bony bridge across the structure; e irregularity in the posterior part of the dorsum sellae, noting deviations from the usual smooth contour; f pyramidal shape of the dorsum sellae, where the dorsum presents a triangular profile

Full size image

The study then examined the relationship between these classifications of the SP and the variations of PP and ST types to determine any statistical significance.

Statistical analysis

The data obtained in this study were analyzed using the SPSS 22 package program. For comparisons between two groups, the Mann–Whitney U test was utilized, while for comparisons involving three or more groups, the Kruskal–Wallis H test was employed. Chi-square analysis was used for the evaluation of categorical data. A significance level of 0.05 was applied, indicating that if p < 0.05, there was a significant difference/dependence, whereas if p > 0.05, there was no significant difference/dependence noted.

Results

The data encompassed a total of 460 patients (average age 39.7), comprising 241 females and 219 males.

Ponticulus posticus

In the analysis of the PP, among 231 individuals on the left side, 77.9% (180 individuals) were found to lack this variation (absent), while 10.8% (25 individuals) exhibited a complete presence, and 11.3% (26 individuals) exhibited a partial presence. A similar distribution was observed on the right side, where 79.2% (183 individuals) lacked the PP, 9.5% (22 individuals) had a complete PP, and 11.3% (26 individuals) had a partial PP (Table 1).

Table 1 Distribution analysis of stylohyoid ligament calcification, sella turcica and ponticulus posticus variations
Full size table

The research also explored whether there were any gender differences in the occurrence of the PP on both sides. The comparative analysis revealed no significant differences between genders in the presence of PP (p > 0.05), indicating a similar occurrence rate among both females and males. Nonetheless, males showed a non-significant tendency toward higher frequencies of the 'complete' PP condition on the left side compared to females. Similarly, on the right side, males had a non-significantly higher occurrence of both 'complete' and 'partial' conditions than females. This suggests that while gender does not significantly impact the presence of ponticulus posticus, there is a slight trend toward more frequent complete and partial forms in males.

Furthermore, the study assessed the association between participants' age and the condition of PP on both sides. The mean ages for the 'absence,' 'complete,' and 'partial' PP groups were 30.2, 37.1 and 32.9 years for the right side and 30.4, 34.8, and 33.2 years for the left side, respectively. No significant age-related differences were found in the condition of PP (p > 0.05), showing that the condition of PP is not correlated with age. However, individuals with a 'complete' condition of PP tended to be older, though this trend was not statistically significant.

Stylohyoid ligament calcification

The calcification of the SP was separately analyzed for the right and left sides, with the highest percentages found in the ‘d’ (24.2%) and ‘e’ (elongated) (19.7%) categories among a total of 380 individuals on the right side. On the left side, among 373 individuals, the ‘d’ (24.4%) and ‘e’ (elongated) (16.9%) categories again had the highest rates (Table 1).

Furthermore, the study assessed the symmetry of styloid processes between the right and left sides. Out of a total of 380 individuals, symmetrical conditions were more prevalent, accounting for 68.4%, indicating that styloid processes tend to exhibit similar characteristics bilaterally.

In this research, we analyzed the degree of symmetry of the SPs between the right and left sides across different genders. No significant gender-based differences was found in the symmetry prevalences of the SP (p > 0.05), suggesting that males and females exhibit comparable rates of bilateral symmetry. Although not statistically significant, there was a trend toward slightly higher symmetry rates among males.

Moreover, the study explored the effect of participant age on the symmetry of SP. The mean ages for the 'symmetric,' and 'asymmetric' appearance groups of SP were 38.2 and 37.8 years, respectively. The analysis indicated no statistically significant age-related differences in symmetry (p > 0.05).

Sella turcica

Regarding ST, an assessment of 363 individuals revealed that the most common category was A, accounting for 56.2% (204 individuals) of cases. These findings indicate a variety of structural characteristics for ST (Table 1).

Finally, the distribution of ST and PP types in the context of normal, elongated, and calcified conditions of the right and left SP has been evaluated. Upon analysis, no statistically significant difference was found between the distribution of ST and PP types and the conditions of the SP (normal, elongated, calcified) (p > 0.05) (Table 2).

Table 2 Distribution of right and left SP ("normal", "elongated", "calcified") between sella turcica and ponticulus posticus types
Full size table

Discussion

Ponticulus posticus

The phenomenon of ligamentous structures ossifying within the body can lead to clinical challenges. These include the potential compression of adjacent anatomical structures and increased complexity in surgeries localized to those regions. A notable manifestation of this is the ossification of the posterior atlantooccipital membrane, which can create a bony arch known as the ponticulus posticus over the vertebral artery groove (Krishnamurthy et al. 2007). This anatomical variation has been extensively studied. Cakmak et al. (2005) utilized a combination of 60 dry atlas bones and 416 lateral cervical spine radiographs to determine the prevalence of ponticulus posticus. They observed that complete formations occurred in 11.7% of the dry bones and 7.2% of the radiographs, while incomplete formations were noted in 3.3% and 6.25%, respectively. A gender-based distinction was also apparent; 80% of the cases with complete arcuate foramen were female, and 20% were male. In contrast, Stubbs (1992) reported a higher frequency of complete foramina in males, while partial foramina were most common among white females.

Saleh et al. (2018) conducted a thorough analysis of 2917 cervical spine CT scans, finding a 22.5% prevalence of ponticulus posticus with a higher occurrence in males. Similarly, Chitroda et al. (2013) investigated the presence and types of ponticulus posticus (PP) using digital lateral cephalograms. They observed that partial forms were more common in females, while complete forms were significantly more prevalent in males. Although not statistically significant, our study also found that the complete type of PP was detected more frequently in males. In addition, Giri et al. (2017) evaluated the presence of ponticulus posticus through lateral cephalograms, reporting a prevalence of 35.7%, which included 30.9% partial and 4.8% complete formations. They concluded that gender did not significantly influence the occurrence of this anatomical feature, a finding that aligns with the results of our study.

In the context of existing literature, our findings contribute additional perspectives on the prevalence and age-related characteristics of PP. Unlike Taitz and Nathan (1986), who reported an increased prevalence of complete formations (30–80 year group) in older age groups, this study did not observe significant age-related differences in PP formation. Similarly, while Schilling et al. (2010) found a higher prevalence of bony bridges in younger age groups (11–20 years and 21–30 years), our results suggest a more uniform distribution across adult ages, regardless of PP completeness. This discrepancy may highlight the influence of demographic and geographical variations on the development of PP, or possibly differences in the methodologies employed across studies. Our findings suggest that the formation of PP is a complex phenomenon that may not be strongly linked to aging or gender within the adult population, contrasting with the clearer age or gender-related trends reported in earlier studies. Further research is necessary to explore these patterns more deeply, particularly in different populations and with larger sample sizes, to better understand the underlying factors influencing PP formation.

Stylohyoid ligament calcification

Eagle's syndrome, characterized by elongation of the styloid process and structural changes in the stylohyoid ligament, presents specific clinical signs and symptoms first described by Eagle. Diagnosis involves both clinical examination and radiographic assessment (Gokce et al. 2008b). Anatomically, the styloid process is situated anteromedially to the facial nerve and medially to the accessory and vagus nerves (Sekerci et al. 2015). The symptoms and signs associated with this syndrome are attributed to the anatomical relationships between the SP and surrounding structures (Gokce et al. 2008b). Consequently, detailed knowledge of the stylohyoid ligament region is crucial before undertaking surgical interventions in the head and neck area (Sekerci et al. 2015).

Gokce et al. (2008b) investigated the prevalence of styloid process elongation in a group of Turkish population using panoramic radiographs (PR). Among 698 PRs analyzed, 7.7% of patients exhibited SPE on at least one side. Significant differences were observed in SPE prevalence between the 10–19, 20–29 age subgroups, and the 30–39, 50–59 age subgroups, which may suggest potential age-related variations in SPE occurrence. However, these results underscored the necessity for further research to investigate factors influencing SPE across different age groups.

MacDonald-Jankowski (2001) employed a modified version of Carroll's classification to categorize the pattern of calcification in the SP. This classification system focused on the center of calcification involved, delineating four regions: tympanohyal, stylohyal, ceratohyal, and hypohyal. The 12 patterns were derived from the calcification patterns in these regions, considering whether the regions are continuous or distinct. This classification approach provided a structured framework for characterizing SP calcification patterns and facilitating comprehensive analysis. Several studies in the literature have utilized this classification method. Altindag et al. (2022) conducted a study examining the prevalence and classification of different patterns of the stylohyoid chain complex using panoramic radiographs. In the examined cases, 86.5% exhibited normal styloid process patterns, while 7.1% showed elongated SP, and 2.2% displayed a calcified stylohyoid ligament. The absence of the stylohyoid chain was noted in 2.8% of cases, while 1.4% had unclassified patterns. Interestingly, the distribution of patterns was symmetric in 80.4% of the stylohyoid chain complexes. Similarly, Omami (2018) reported the prevalence of SP patterns as 61.2% regular, 17.2% elongated, 17.8% calcified, and 3.2% undetected using panoramic radiographs. 81.6% of cases exhibited the symmetrical appearance in both side.

In our study sample of 380 patients, similar results were found in the distribution of SP types compared to Altindag et al. (2022) and Omami's (2018) studies, which utilized panoramic radiographs. Specifically, the styloid process was classified as regular in 55.9%, elongated in 18.3%, calcified in 25.7%, and undetected in 0.15%. While our results showed a slightly lower prevalence of regular patterns and a higher percentage of calcified patterns compared to these two studies, the overall distribution remained consistent. However, it is noteworthy that the percentage of symmetric patterns, indicating identical styloid process types bilaterally, was lower in our study (68.4%) compared to others.

This disparity suggests potential variations in anatomical symmetry within different populations or could be attributed to differences in imaging modalities. Omami's (2018) recommendation for further morphometric analysis of the stylohyoid complex using computed tomography aligns with our methodology, highlighting the utility of advanced imaging techniques in enhancing understanding of these anatomical variations. While panoramic radiography offers benefits like accessibility, cost-effectiveness, and minimal radiation exposure, it may inadvertently distort the measurements of the styloid process due to magnification and distortion. In addition, the overlap of anatomical structures, such as the mandible and cervical vertebrae, may obscure the visibility of the styloid process in panoramic images. Variability in patient positioning further complicates matters, potentially leading to inaccuracies in measurements and diagnostic errors (Monsour and Young 1986).

The decreased prevalence of regular and symmetrical patterns in our study compared to those reported in panoramic radiography-based studies suggests that CBCT imaging may offer a more precise portrayal of the styloid process and its variations. Öztunc et al. (2014) investigated the structural features of the SP using CBCT in a group of patients experiencing orofacial pain. Through a retrospective analysis of clinical and radiographic records of the patients, the study found that 46% had non-elongated SP, while 13% showed left-sided elongation, 8% right-sided elongation, and 33% bilateral elongation. Increased prevalence of neurological symptoms, excluding headache, was observed in patients with elongated SP, suggesting a potential link between SP morphology and symptomatology. Thus, careful consideration of imaging modalities is imperative for accurately assessing the morphology of the styloid process and stylohyoid ligament, particularly when investigating for potential pathologies or symptoms linked to these structures.

Sella turcica

The sella turcica is a saddle-shaped depression located in the sphenoid bone at the base of the skull, which contains and protects the pituitary gland. This structure serves as a critical landmark in neuroanatomy, radiology, cephalometric analysis, and transsphenoidal surgery, owing to its proximity to important neural and vascular structures (Iskra et al. 2023).

Several studies have been conducted on the morphology of the sella turcica across various health statuses. While some studies have assessed its morphology in healthy individuals (Alkofide 2007; Magat and Sener 2018; Valizadeh et al. 2015; Sönmez et al. 2024; Yasa et al. 2017b), others have examined morphological variations in patients with different syndromes (Axelsson et al. 2004; Yasa et al. 2017b; Yalcin. 2020) or systemic diseases (Sönmez et al. 2024; Bavbek and Dincer 2014). These assessments often utilize lateral cephalometric radiographs (Polat et al. 2020; Axelsson et al. 2004; Alkofide 2007; Magat and Sener 2018; Valizadeh et al. 2015); however, CT and CBCT (Yasa et al. 2017b; Sönmez et al. 2024; Yalcin. 2020) are increasingly employed to provide more detailed insights. According to Axelsson et al. (2004), the morphology of the sella turcica can be classified into six types: normal, oblique, extremely low sella turcica, bridging, irregularity, and pyramid. Consistent with our findings, the normal type of sella turcica was the most commonly observed among healthy individuals, despite varied prevalence rates (Alkofide 2007; Axelsson et al. 2004; Shah et al. 2011; Sönmez et al. 2024).

Variations in prevalence rates are thought to be influenced by differences in populations or the imaging methods used. Superimpositions in two-dimensional images pose significant challenges in determining sella morphology, especially when distinguishing between a true sella bridge and a pseudo bridge (Ortiz et al. 2018). Consequently, CBCT was utilized in our study to more accurately determine the morphology of the sella turcica.

This study also provides a comprehensive analysis of the relationships between styloid process calcifications, ponticulus posticus and sella turcica morphology. Sekerci et al. (2015) conducted a study using CBCT to investigate the relationship between the presence of PP and an elongated SP, reporting a statistically significant correlation. Similarly, Tassoker et al. (2017) evaluated the relationship between sella turcica bridging and PP, finding a strong association. However, like the findings reported by Shahidi et al. (2022), our study found no significant relationship between PP and SPE. In contrast, due to the small sample size in our study—only seven cases exhibited ST bridging—our ability to establish a significant statistical correlation was limited.

The present study, conducted within a Turkish population, has several limitations that must be considered when interpreting the findings. One significant limitation is the potential lack of generalizability of the results to other populations. Genetic, and environmental factors that are unique to the Turkish population might influence the prevalence and characteristics of the anatomical features studied. Consequently, the findings may not directly apply to populations with different ethnicities or environments. In addition, the small sample size, particularly in some variables, may have further limited our ability to detect significant associations and correlations. Future research needs to be performed in different populations to confirm the findings and extend understanding of these anatomical variations.

Conclusion

This study contributes valuable insights into the anatomical variability and symmetry of the SP, ST, and ponticulus posticus. The findings underscore the complexity of these structures and their independence from each other and from factors such as gender and age. These results have potential implications for clinical practice, particularly in the accurate diagnosis and treatment of conditions related to these anatomical features. Further research is encouraged to explore the clinical significance of these findings and their potential impact on patient care.