Prevalence of Stylohyoid Complex Elongation among Patients Attending RAK College of Dental Sciences Clinic.

OBJECTIVE: To investigate into the prevalence of the SP complex elongation among patients attending RAK Dental College Clinic.
MATERIAL AND METHODS: A 3234 radiographic images of patients aged ≥18 years were examined. The O'Carroll (1984) classification of stylohyoid complex was used. Age, gender, ethnicity and patterns of calcification were recorded and analyzed. Chi-squared and ANOVA tests were used to detect potential differences.
RESULTS: Male to female ratio was 1.9:1. There were 1150 (35.6%) subjects in age group-I (18-39) and 2084 (64.4%) subjects in the age group-II (≥40). The mean age was 38.12 (±13.2). Fifty seven % (1836) of the subjects were eastern Asians, 671 (21%) Africans, 325 (10%) Middle east, 254 (8%) Europe, and 148 (4%) other ethnicities. A normal SP was found in 1601 (49.51%) of the images, elongated in 903 (27.92%), calcified in 406 (12.55) and undetected in 324 (10.2%). The elongated and the calcified styloid processes were more common in males (p=0.0078). The elongated and the calcified SP were more frequent in group II subjects (p=0.0004). Eastern Asians had higher percentage of elongated and calcified SP p= 0.00567.
CONCLUSION: Although 1601 (49.51%) of subjects had normal SP, the study revealed a high prevalence of SP elongation among eastern Asians. There is a strong association between the age and the SP elongation. It is crucial to include the head and neck symptoms of non-odontogenic origin in the differential diagnosis of Eagle's syndrome. The study recommends further investigation using some advanced imaging techniques.

Introduction:

Styloid process (SP) is a thin bony projection extending from lower surface of the temporal bone in an anterior-inferior route bilaterally. The stylohyoid complex comprises the styloid process, stylohyoid ligament, and the lesser cornu of the hyoid bone. It develops from the second pharyngeal pouch; the Reichart cartilage. Three muscles are attached to SP, namely the stylopharnygeous, stylohyoid and styloglossal muscles, in addition to the stylohyoid and stylomandibular ligaments. Anatomically, it has an intimate close contact with the upper portion of carotid space and its contents, including the cranial nerves V, IX (). Its normal length ranges between 20-30 mm; however, it shows variation among different people ().

It has been suggested that the stylohyoid ligament calcification refers to an elongated SP, which was invariably observed accidently on panoramic radiographs. When a SP extends beyond 30 mm in length, it is considered elongated and may be presented unilaterally or bilaterally (, ).

A small percentage of population (4%) exhibit elongation of the SP, and it has been invariably noticed as an incidental radiographic finding (, ). Among patients with elongated SP, 4%-10% are presented with symptoms, known as Eagle syndrome (, ). The commonly associated symptoms are neck or throat pain, dysphagia, foreign body sensation, facial pain tinnitus, otalgia and occasionally limitation of mandibular movement (-) O’Carroll () reported that about 8% of patients with elongated SP presented with associated symptoms including painful neck, pain on swallowing, sensation of blocked throat in the throat and pain on turning the head.

The etiology of the SP elongation is unknown. However, some authors suggested that it has a congenital back ground (, ), while others believe that local chronic irritations, hormonal disorders, trauma from surgery, persistence of mesenchymal elements, osseous tissue growth and mechanical stress or trauma during development of SP may lead to calcification and elongation of the SP (-).

Several authors have described various classification patterns of an elongated SP including radiographic classification for the calcified stylohyoid complex. In general, the following three radiographic patterns are presented: elongated, segmented and pseudoarticuated. In addition, the author has stated the following four patterns of calcification: calcified outline, partially calcified, nodular complex and completely calcified (, ).

A diagnosis of SP elongation or stylohyoid ligament calcification is established using radiographic imaging such as Orthopantomograph (OPG), Cone Beam Computed Tomography (CBCT) and Computed Tomography (CT) Scan. Although the panoramic radiograph is a two dimensional x-ray, it has been found to provide adequate information for epidemiological studies and its imaging technique makes it convenient for imaging findings in the maxillofacial region ().

The main aims of this study were to find out the frequency of elongated SP among patients attending RAK College of Dental Sciences (RAKCODS) Clinic and to investigate the calcification patterns of elongated SP using archived panoramic radiographs between the years 2017 and 2018. Our hypothesis was a high prevalence of SP elongation among the Asian subcontinent population.

Materials and Methods:

This study was approved by the RAK Ethics and Research Committee of RAK Medical and Health Sciences University. All archived digital panoramic radiographs (OPGs) in the radiology department, RAK College of Dental Sciences taken between January 2017 and December 2018 were retrieved and analyzed anonymously for elongation of the SP and patterns of stylohyoid complex calcification. The radiographs were taken for oral diagnostic purposes using Panoramic X-ray (Model: GEN-XRAY25, Manufacturer: Gendex Panoramic, USA) under standard conditions. The OPGs were viewed using HP a 19-inch HP Flat Panel LCD Monitor, resolution at 1000:1 contrast ratio and 1440 x 900 resolutions. The subjects were given their consent during the first clinical examination visit declaring that the collected data may be used for research purposes. Only the subjects aged18 years and above were included in the study. Any OPGs with technical fault, elongated or indistinct images were excluded. One of the authors went through a short intensive training under a certified radiologist in the radiology department to standardize the process of radiographic examination. The intra-observer consistency was tested by examining 22 randomly selected OPGs at different time intervals and the consistency of the interpretation was found to be satisfactory (Kappa= 0.813).

The OPG images are available only at the radiology department; therefore, O’Carroll (1984) method of stylohyoid complex classification was applied. The SP was ranked ‘‘regular” if the SP did not cross the mandibular foramen level (Figure 1, patterns A to D); ‘‘elongated” when it appeared extended beyond the mandibular foramen and continuous with the base of the skull (Figure 1, pattern E); ‘‘calcified” when it extended below the mandibular foramen but not continuous with the cranial base (Figure 1, pattern F to K); and ‘‘undetected” if it could not be traced on the panoramic image. In this study, patterns A, B, C and D were considered to be normal SP, pattern E an elongated SP and patterns F, G, H, I, J and K calcified stylohyoid (SH) ligaments. Figure 2 shows the four main classifications of stylohyoid complex followed in this study, regular (a); elongated (b); calcified (c); undetected (d).

Figure 1

Demonstrates O’Carroll’s classification of the stylohyoid complex: Regular; patterns A through D, Elongated; pattern E, Calcified; patterns F through K, and absent; pattern L (adapted from O’Carroll’s, 1984).

Figure 2

The four main classification of stylohyoid complex followed in this study, regular (a); elongated (b); calcified (c); undetected (d).

The available details regarding age, gender, ethnicity, right and left sides, types and patterns of calcification were collected and were analyzed using the SPSS version 21 program (SPSS, Chicago, IL, USA). Chi-squared and ANOVA tests were applied to find out any significance differences between age groups, gender and ethnicity. Also, the subjects were stratified into two age groups; 18-39 years (group-I) and 40 years and above (group-II).

The current population of the United Arab Emirates is 9,653,558 as determined on April 20, 2019, based on the latest United Nations estimates. The UAE population is multiethnic in nature and the expatriates outnumber the local people (Emiratis). The males form about 72% of the entire population, while 28% are females. The local people (Emiratis) form only 11% of the total population, while the majority of the expatriate are Indians (28%), Pakistan (13%), Bangladesh (7%), Philippines (6%) and rest from other countries including Middle East Arabs.

Results

A total of 6563 patients’ digital panoramic radiographs were collected; 3329 images were excluded because of the age (subjects below 18 years) or poor image quality including errors in positioning or exposure. Only 3234 OPGs were considered valid for the study. The number of male subjects was 2112 (65%), and the number of female subjects was 1122 (35%). Male to female ratio was 1.9:1. There were 1150 (35.6%) subjects in the age group-I (18-39) and 2084 (64.4%) subjects in the age group-II (40 and above). The age range was 18-68 years, the mean age being 38.12 (±13.2). The ethnic group frequency of the subjects is shown in Figure 3, with the eastern Asians forming the majority of the subjects. Figure 2 shows the 4 main classifications of the stylohyoid complex that was used in this study. Table 1 demonstrates the 12 patterns of O’Carroll’s classifications that were observed during years 2017 and 2018. The SP was classified as regular (normal) (A-D) in 1601 images (49.51%), elongated (E) in 903 (27.92%), calcified (F-K) in 406 (12.55%) and undetected (L) in 324 (10.2%). The distribution of the SH complex patterns among the various ethnic groups is shown in Table 2.

Figure 3

Frequency of ethnic population

Table 1

Patterns of the stylohyoid complex calcification among subjects.

Classification	Pattern	Side	2018	2017	Total	Percentage
Regular	A	Rt	150	14	336	5.19%
		Lt	156	16
	B	Rt	202	40	458	7.08%
		Lt	178	38
	C	Rt	302	120	790	12.21%
		Lt	264	104
	D	Rt	702	198	1618	25.02%
		Lt	560	158
Elongated	E	Rt	448	512	1806	27.92%
		Lt	342	504
Calcified	F	Rt	14	14	54	0.83%
		Lt	14	12
	G	Rt	36	70	194	3.00%
		Lt	30	58
	H	Rt	6	8	20	0.31%
		Lt	2	4
	I	Rt	38	122	304	4.70%
		Lt	42	102
	J	Rt	16	34	90	1.39%
		Lt	12	28
	K	Rt	24	58	150	2.32%
		Lt	18	50
Undetected	L	Rt	242	142	648	10.02%
		Lt	174	90
Rt, right; Lt, left

Table 2

Distribution of SH complex patterns among ethnic populations

Stylohyoid complexclassification	Ethnic populations
	African (%)	Middle Eastn (%)	East Asian (%)	Europen (%)	Othersn (%)	Total
Regular	328 (10.1)	51 (1.6)	998 (30.9)	121 (3.7)	103 (3.2)	1601
Elongated	218 (6.7)	129 (4.0)	502 (15.5)*	31 (1.0)	23 (0.7)	903
Calcified	84 (2.6)	104 (3.2)	189 (5.8)*	15 (0.5)	14 (0.4)	406
Undetected	41 (1.3)	41 (1.3)	147 (4.5)	87 (2.7)	8 (0.2)	324
Total	671 (20.7)	325 (10.0)	1836 (56.8)	254 (7.9)	148 (4.6)	3234

*East Asian shows high prevalence of SH complex calcification compared to other ethnic groups, p= 0.0056

When the O'Carroll's SP classification was adapted, our results showed that the majority of the subjects exhibited regular pattern 1601 (49.51%), followed by elongated and calcified with 903 (27.92%) and 406 (12.55%) respectively. The elongated and the calcified styloid processes are more common among males (p=0.0078). When age groups are considered, both the elongated and the calcified styloid process patterns were more frequent among subjects of group II (p=0.0004). Also, the coefficient of determination (R Square)) showed strong positive correlation (R2=0.98).

There has been strong association between SH complex patterns and ethnic groups. The elongated and the calcified patterns were significantly prevalent among eastern Asians (46.55%), p= 0.00567 compared to other ethnicities (Figure 4). Generally, more than 80% of the subjects exhibited symmetrical patterns.

Figure 4

High frequency of calcified stylohyoid complex elongation among East Asian; p= 0.00567

Discussion:

An OPG is a widely used view in dental clinical practice and is accepted as a diagnostic tool for detection of stylohyoid complex elongation and calcification. To our knowledge, the sample size of this study is probably one of the largest ever investigating the SH complex calcification patterns. The current population of the United Arab Emirates is above 9.5 million, which is a diverse community comprising mainly eastern Asians (58%) in addition to other ethnicities including Middle Easterners, Africans, Caucasians and other minorities. Many studies have been carried out exploring the prevalence and patterns of stylohyoid complex elongation and calcification (, , -, ), however, the majority of the studied samples were of the same population. In the current study, our sample is diverse comprising 4 main populations, thus making it a good comparative study model. It was the observation of the authors that many of the Asian patients attending the dental clinic of RAKCODS exhibited one form or the other of stylohyoid complex elongation or calcification and this was the underlying reason for this investigation. It was difficult to retrieve the clinical data of the subjects involved in this study; therefore, the correlation between the stylohyoid complex patterns and the clinical symptoms or signs was not sought.

Our findings reveal that the majority of the subjects presented with the regular pattern of SP 1601 (49.51%). In this study, the incidence of elongated SP is comparatively higher than many of the previously reported studies (, ). Mathew et al., () studied the prevalence of elongated SP and calcification patterns in South Kerala population using panoramic radiographs, and they found higher incidence than our study (35%). Bader, 2017 () investigated the frequency of elongated SP among Saudi geriatric patients (> 60 years), and they found much higher incidence (44%). The variation in the reported incidences could be attributed to many factors including the age range of the samples, methods of classification used in analyzing radiographs and the ethnicity of the population. When both the elongated and calcified SP are combined, our results show male predominance (p=0.0078). The high male prevalence of elongated SP in this study is in line with many reported studies (-). However, a significant prevalence of elongated SP among females has also been reported () and in other report it was higher in females, but statistically insignificant (). Jung et al., 2004 () reported that the normal length of female SP is shorter compared to male SP and the SP increases in length by 0.05 mm per year. The latter probably explains the high incidence of SP elongation with age progress. Furthermore, the authors suggested that the SP should be considered elongated if it exceeds 45 mm according to their study. However, they made the proposal in 2004, and to our knowledge none of the investigators adapted their suggestion. A recent study by Sridevi et al., () the length of SP was measured in 500 panoramic radiographs and revealed that the mean length of SP in females was 3.7 cm on the right side and 3.8 cm on the left side of the studied radiographs, whereas the mean in males was 3.4 cm on the right side and 3.3 cm on the left side. The author concluded that the length of the SP was significantly longer in females than in males. The latter authors advocated the need for reevaluation of the normal range of SP length.

In the current study, a statically significant prevalence of SP elongation and calcification was found among the subjects of Eastern Asian (p=0.0056). Although, O’Carroll [11] revealed no specific ethnic predilection in his study, the studies on SP elongation and calcification among multiple ethnic populations in literature are very scarce.

Our findings revealed a statistically significant prevalence of SP elongation and calcification among the subjects of the age group-II (40 years and above) compared to the group-I (18-39 years) subjects (p=0.0004). Considering the previous literature and our study as well, we believe that there is an obvious correlation between the age and the SP elongation. In a study including only subjects > 60 years () the prevalence of SP elongation was 39 (44%) among males. In contrast, Gokce et al., () reported 54 (7.7%) prevalence of SP elongation and found no correlation between the age subgroups and the SP elongation. The authors attributed the lack of correlation to the abnormally distributed age groups in their study.

In the current study, the bilateral elongation was the most common pattern compared to the unilateral and this is consistent with other studies (, , ). A high degree of symmetry has also been reported by a recent study in Libya (). However, there was inconsistency in the reported male and female distribution when unilateral or bilateral SP elongation is considered. It is inevitable to question the relevance of unilateral or bilateral SP elongation in the absence of any clinical symptoms. Since the etiology of the condition has not been defined yet, this feature is probably of little significance in this context.

In 324 (10.02%) of the subjects, the SP was radiographically invisible and we could not determine whether it was anatomically absent or it was radiographically invisible due to some technical reasons.

The stylohyoid ligament is comprised of fibrous tissue and may undergo partial or complete calcification causing various degrees of clinical symptoms in the head and neck region. There is always a potential for the clinicians to miss or fail to diagnose symptoms related to the SP elongation. Therefore, the latter should be considered in the differential diagnosis and management of head and neck symptoms not related to odontogenic origin.

Conclusions

The data available from the literature and the current study reveals potential association of SP elongation with age progression. Therefore, the age at which the SP is considered elongated should be revised. The eastern Asian population exhibited high prevalence of SP elongation and calcification compared to other populations. Therefore, oral physicians should be aware of the ethnic distribution of SP elongation and potentially related symptoms. To the best of our knowledge, this is the first study exploring the prevalence of the stylohyoid complex calcification among the United Arab Emirates population. The authors highly recommend further investigation to include clinical data record and standardized measurement of the SP including CBCT imaging.