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 Table of Contents  
ORIGINAL ARTICLE
Year : 2022  |  Volume : 28  |  Issue : 2  |  Page : 119-125

Cone-Beam Computed Tomography Evaluation of Morphology and Orientation of Styloid Process and Prevalence of its Elongation in Age and Gender: An Institutional-Based Retrospective Study - A Dentist Perspective


Department of Oral Medicine and Radiology, Meenakshi Ammal Dental College and Hospital, Chennai, Tamil Nadu, India

Date of Submission14-Mar-2022
Date of Acceptance25-Mar-2022
Date of Web Publication21-Sep-2022

Correspondence Address:
S Priyadharshini
Department of Oral Medicine and Radiology, Meenakshi Ammal Dental College and Hospital, Chennai - 600 095, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/indianjotol.indianjotol_46_22

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  Abstract 


Background: Styloid process (SP) is a cylindrical, cartilaginous bone that projects downward, medially from petrous part of the temporal bone on right and left sides. There are variations noted in the SP which results in impingement on nearby vital structures and can cause annoying orofacial pain. Cone-beam computed tomography (CBCT) gives an accurate image without superimposition of adjacent structure. Aim: This study aims to investigate the three-dimensional orientation, length, and morphological variations of the SP using CBCT. Materials and Methods: One hundred and twenty CBCT images from the age of 20–60 years were retrieved and further divided into three groups (Group I, II, III). The length, anteroposterior angulation (APA), and mediolateral angulation (MLA) of styloid were measured along with its type of classification of elongation and calcification pattern were recorded. Statistical analysis was done using SPSS version 28. Results: In our study, the mean length, APA, and MLA of both right and left SPs were found to be 3.05 ± 1.1 cm, 31.7° ± 6.2°, and 67.3° ± 5.8°, respectively. 41.7% was the prevalence of elongation. No significant difference in prevalence, among age group observed. Type I and Type II classification of elongation was predominantly seen. Type B pattern of calcification was found to be statistically highly significant (P = 0.000) on both right and left sides. Conclusion: Diversity of SP in length, angle, and morphology can occur within individuals across populations and among gender; these variations need to be considered in symptomatic patients.

Keywords: Angulation, calcification, cone-beam computed tomography, length, morphology, prevalence, styloid process elongation


How to cite this article:
Priyadharshini S, Gopal K S, Srinivasan S. Cone-Beam Computed Tomography Evaluation of Morphology and Orientation of Styloid Process and Prevalence of its Elongation in Age and Gender: An Institutional-Based Retrospective Study - A Dentist Perspective. Indian J Otol 2022;28:119-25

How to cite this URL:
Priyadharshini S, Gopal K S, Srinivasan S. Cone-Beam Computed Tomography Evaluation of Morphology and Orientation of Styloid Process and Prevalence of its Elongation in Age and Gender: An Institutional-Based Retrospective Study - A Dentist Perspective. Indian J Otol [serial online] 2022 [cited 2022 Sep 25];28:119-25. Available from: https://www.indianjotol.org/text.asp?2022/28/2/119/356454




  Introduction Top


Styloid process (SP) is a cylindrical, long, slender cartilaginous bone which arises from petrous part of temporal bone on the right and left sides in front of stylomastoid foramen. It projects downward, forward, and slightly medial.[1] SP develops from Reichert's cartilage of 2nd branchial arch. The ossification of the SP starts at the end of pregnancy in fetal stage and undergoes calcification up to the first 8 years of life. The postnatal styloid chain comprises the SP of the temporal bone, the stylohyoid ligament, and the lesser horn of the hyoid bone. Ossification of this chain may involve a number of individual segments, separated by pseudoarthrosis.[2],[3]

The normal length of SP ranges from 20 to 25 mm. The length of SP when exceeds 30 mm, it is called “elongated SP (ESP).” ESP may be one of the causes for annoying orofacial pain. This is called Eagle's syndrome which was first described by Watt W. Eagle, an otorhinolaryngologist in 1937. It develops unilaterally or bilaterally, causing recurrent throat pain, dysphagia, pain on opening the mouth, chewing, or a facial pain.[4] The SP is in close proximity to neurovascular structures including both the internal and external carotid arteries, the internal jugular vein, and cranial nerves IX, X, XI, and XII. Compression of internal or external carotid artery by SP results in a rare condition called stylocarotid artery syndrome a vascular variant of Eagle syndrome. It can result in neurologic symptoms including transient ischemic attack, syncope, and even stroke.[5] The accentuated medial deviation may invade the tonsil causing painful symptoms and anterior angulation can result in mucosal irritation and pressure on vital structures in the tonsils.[6]

Variations are noted in terms of length of the process, thickness of segments, angle and direction of deviation, and degree of ossification. These variations can be viewed in two-dimensional radiographs such as anteroposterior (ALA), lateral oblique view of mandible, panoramic projections, and cephalometric radiographs. However, the drawback of these two-dimensional imaging is superimposition of different bony structures such as the mandible, teeth, or base of the skull over the styloid. Hence, three-dimensional computed tomography (3D-CT), Cone-beam CT (CBCT) can show stylohyoid complex variations clearly, and make the evaluation more precise.[7],[8] Advantages of CBCT over CT are submillimeter spatial resolution, less radiation dosage, and shorter time for imaging.[9] Hence, in our study, CBCT was used efficiently for the studying the variations of SP by measuring its length, ALA, and mediolateral angulations (MLA) and its morphological changes such as classification and calcification.

Aim and objectives

This study aims to investigate the 3D orientation, length, and morphological variations of the SP using CBCT.

  • To analyze the length and angulation of SP
  • To evaluate the morphological variations of SP
  • Determine the prevalence of ESP among various age groups and gender.



  Materials and Methods Top


This study was performed as a retrospective analysis on CBCT images acquired from the dental archives of the Department of Oral Medicine and Radiology of Meenakshi Ammal Dental College. The sample size calculation was done using SPSS 28.0 software (IBM SPSS Inc., Chicago, IL, USA). Ethical clearance was obtained from the institutional review board. One hundred and twenty CBCT images with 240 SP of patients between 20 and 65 years which included 60 males and 60 females where the entire SP from point of attachment to petrous temporal bone to tip was covered were examined. The images were recorded using PLANMECA PROMAX 3D MID PROFACE CBCT machine in DICOM format and were imported and analyzed using RadiAnt DICOM viewer 2021.1 software. Images which did not include SP on both sides in the field of view, Images of patients with a history of any kind of developmental abnormalities were excluded. The sample of 120 CBCT images was divided into three age groups Group I (20–35 years), Group II (36–50 years), and Group III (51–65 years). Each group consists of 20 images of an equal number of males and females.

All the images were sliced at 10 mm size thickness and the sagittal plane of CBCT images were tilted in such a way that the Frankfort horizontal plane is parallel to horizontal reference line. Then base of the SP was identified as the point of attachment of styloid to petrous part of temporal bone by thin radiolucent line and this was confirmed by placing reference line at that point in both sagittal and coronal planes [Figure 1]. The study parameters were assessed in sagittal and coronal planes.
Figure 1: Base of the styloid process is identified in both sagittal and coronal planes

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The length of each SP is measured in sagittal plane, from base to the tip of the calcified portion irrespective to the number of segments [Figure 2]. SP orientation is determined by it anteroposterior and MLA. This is done similar to method illustrated by Ilgüy et al. in 2012.[10] In sagittal plane, a vertical line passing from cranial base of the process which is also vertical to the Frankfort plane is drawn. The angle formed between long axis of SP to this vertical line is measured as anteroposterior angulation [Figure 3]. In the coronal plane, MLA was determined as the angle formed by the line connecting the base of right and left SP and its long axis [Figure 4].
Figure 2: The length of each styloid process measured in sagittal plane, from base to the tip of calcified portion irrespective to the number of segments

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Figure 3: A line is drawn along the body of styloid process to meet the vertical line, thus the angle formed between them is measured as anteroposterior angulation

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Figure 4: Mediolateral angulation is determined as the angle formed by the line connecting the base of right and left styloid process and its long axis

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The normal length of SP is considered to be below 3 cm and was denoted by letter “N.” Length more than 3 cm is considered as ESP. Based on Langlais et al., in 1986,[11] type of classification of ESP and type of calcification pattern are given in [Figure 5] and [Figure 6].
Figure 5: Type of classification of elongated styloid process. Type I-Elongated; Type II-Pseudoarticulated; Type III-Segmented

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Figure 6: Type of classification of styloid process. (a) Calcified out line; (b) Partially calcified; (c) Nodular outline; (d) completely calcified

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  Results Top


One hundred and twenty CBCT images with 240 SPs were analyzed between age of 20 and 65 years. All the data were recorded for both right and left side SP and tabulated into Microsoft Excel sheet and statistical analysis was done using SPSS 28.0 software. Pearson's correlation coefficient was used to find the possible association between length, angulation of styloid and age groups. The correlation coefficient values of the variables were found out and the confidence interval was set as 95% and P < 0.05 was considered to be statistically significant. Mann–Whitney U-test was performed to evaluate the distribution of various numerical parameters across gender. Chi-square test was performed to find out the significance between calcification and other parameters and P < 0.05 was considered to be statistically significant.

The mean age of total population taken in study was 40.8 ± 13.9 years. In our study, the mean length, ALA angulation (APA), and MLA of both right and left SPs were found to be 3.05 ± 1.1 cm, 31.7° ± 6.2°, and 67.3° ± 5.8°, respectively. Not much difference was seen in values among all the three age groups. As shown in [Table 1], descriptive analysis of mean and standard deviation of length, anteroposterior angulation, and MLA in male and female included in the study. The mean length of right and left SP among males was 3.5 ± 1.44 cm and 3.2 ± 1.25 cm and among female was 2.7 ± 0.59 cm and 2.8 ± 0.75 cm, respectively. With respect to mean APA among male right side was 32.2° ± 6.89° and left side was 31.5° ± 6.12° and among females' right side was 32.0° ± 5.73° and left side was 31.0° ± 6.41°, respectively. Meanwhile, the mean MLA of right and left SP among male was 66.9° ± 5.94° and 69.5° ± 6.18° and among females was 65.9° ± 5.05° and 67.0° ± 5.84°, respectively.
Table 1: Descriptive analysis of mean and standard deviation of length, anteroposterior angulation and mediolateral angulation in male and female included in the study

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As shown in [Table 2]a and [Table 2]b, the analysis of the distribution of right length and left mediolateral angle among gender by Mann–Whitney U-test the distribution of length of SP on the right side had a significant difference (P = 0.008) in relation to gender (males had more ESP on the right side). Furthermore, the left MLA had a significant difference (P = 0.008) with respect to gender (males had prominent mediolateral angle compared to females).


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[Graph 1]: The prevalence of ESP among 120 patients with 240 SPs. With respect to the prevalence of ESP among 240 SPs, 100 (41.7%) were elongated and 140 (58.3%) were nonelongated. Among gender, male had 57 (47.5%) and females had 43 (35.8%) elongated styloid process. Male had higher prevalence of elongation compared to female. However, there was equal prevalence of elongated styloid (41.25%) seen in all three the age groups (Group I, II and III).



With respect to the distribution of type of elongation among 100 ESP: Type I was present in 41; Type II was seen in 42; and Type III was seen in 17. There was no significant difference between right and left sides, age and in gender. In terms of the type of calcification partial calcification, Type B was predominantly seen which was statistically significant (P = 0.000) on both right and left sides using Chi-square test.

As show in [Table 3], Pearson's correlation between age, length, anteroposterior, and MLA on the right and left side. [Graph 2], [Graph 3], [Graph 4: Highly significant correlation coefficient (P = 0.000) between right and left sides length, anteroposterior angle, and mediolateral angle. There is highly significant correlation coefficient (P = 0.000) between right and left sides length, anteroposterior angle, and mediolateral angle. Furthermore, there was significant correlation coefficient between right length and right mediolateral angle (P = 0.040), left length and left mediolateral angle (P = 0.069), and right anteroposterior angle and right mediolateral angle (P = 0.013).
Table 3: Pearson's correlation between age, length, anteroposterior and mediolateral angulation on right and left sid

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  Discussion Top


SP is a long slender bony structure attached to petrous part of temporal bone in front of the external auditory meatus. Calcification or ossification of stylohyoid chain, which includes the SP, stylohyoid ligament, and the hyoid bone leads to elongation of this process. Several theories were proposed by Steinmann between 1968 and 1970 to explain etiopathogenesis, which are considered valid even today namely, theory of reactive hyperplasia, theory of reactive metaplasia, and theory of anatomic variance.[12],[13] This variation can be easily assessed using X-rays. Two-dimensional imaging modalities are cheap and easily available but they have a drawback of superimposition of adjacent structure. CBCT being 3D imaging is more useful in accurate evaluation with minimal radiation compared to CT.

The normal length of SP measures between 2.5 and 3 cm. More than 3 cm is considered to be elongated and can appear unilateral or bilateral. In our study among 240 SP, the minimum and maximum length recorded were 1.21 cm and 7.85 cm, respectively and 100 were elongated processes (>3 cm) of which 63 were unilateral elongation and 37 were bilateral elongation.

The mean length of 240 SPs in our study was 3.05 ± 1.1 cm. Whereas study done by Sudhakara Reddy et al.[14] in 2013, using 260 OPG images reported mean length of 3.67 ± 0.62 mm. The length of styloid was slightly higher in males compared to females in our study. However, in a OPG study among North Indian population, elongation was observed more in female.[15] This may be due to more female samples taken for the study, but in our study, there was equal number of males and females in all the three age groups. With respect right-side SP length was found to be statistically significant with male gender which similar to study by Jamal et al.[16] in 2019 study in Saudi Arabian population. Phulambrikar et al.[15] observed the length of SP steadily increased between 5 and 24 years and then remained stationary between 25 and 34 years and then marginally increased with age. This pattern of distribution in length among age groups was not observed in our study which could be due to broader age range and narrow age group intervals considered in their study. The measurement of APA and MLA was helpful in determining the normal orientation of SP in population. Yavuz et al.'s[17] in 2007, study observed mean APA of 33.6° on the right side and 36.7° on the left side among 51 subjects using lateral skull radiographs which was in accordance with our study. Onbas et al.[18] in 2005, an MDCT study and Buyuk et al.[19] in 2017, a CBCT study, showed increased value in APA compared to our study because in both these studies there was difference in horizontal reference plane considered to measure the APA. A significant correlation of left APA to left length is seen in our study which is in accordance with Kalabalik and Şahin.[20] in 2020. The mean MLA in our study was in accordance other studies namely Ramadan et al,[7] and Ilgüy.[10] There was a positive correlation between APA and MLA of right side in Andrei et al.[2] in 2012. This was also observed in our study.

The prevalence of ESP in our study was 41.7% which was comparatively less than study done by in 2017 (56.6%) in Chennai population using 100 CBCT images.[21] Our study was in accordance with Bagga et al.[22] in 2020 (45%) which was an OPG study in North Indian population. Whereas study in Northwest Indian population prevalence of 27.3% was observed.[23] The prevalence of ESP in other ethnicity was recorded as, in Brazilian 43.89%,[24] Turkish 15.1%,[1] Saudi Arabian 11%,[25] and Greek 26.7%.[26] Type I elongation was more common in OPG studies,[27],[28] whereas in our study along with Type I, pseudo articulated, Type II was also commonly seen. Regarding calcification pattern of styloid process, partially calcified type B pattern (69. 5%) was statistically significant among other patterns in our study. This was in accordance to Bagga et al 2020.[22] However, Type A (41%)[21] and type D (58%)[14] were predominantly reported among studies done in similar population. Thus, the diversity of SP in length, angle, and morphology can occur within individuals across populations and among gender; these variations with respect to SP need to be considered in symptomatic patients.


  Conclusion Top


ESP is most often found as an incidental finding in a radiograph and not necessarily signify Eagle's syndrome as majority of individuals exhibit it as an anatomical anomaly without symptoms. Alternatively, the possibility of Eagles syndrome must be considered while handling cases of head and neck pain which is often underdiagnosed. Consequently, it leads to underestimation of the incidence of this syndrome and patients might have to undergo unnecessary treatments. Thus, it is important for dental practitioners to be aware of these variations, their anatomical basis and the prevalence of elongation in population, and a proper imaging modality for correct diagnosis.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]
 
 
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  [Table 1], [Table 2], [Table 3]



 

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