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Investigation of the relationship between "Sella Turcica Bridge" and "Ponti cu I us Posticus": A Lateral Cephalometric Study/Investigacion sobre la Relacion entre "Puente Silla Turca" y "PonticuIus Posticus": Un Estudio Cefalometrico lateral.

INTRODUCTION

The atlas is the first cervical vertebra of the spine. This cervical vertebra has several morphologic features that differentiate it from other vertebrae. Ponticulus Posticus (PP) is a variation occuring on the atlas vertebra (Bayrakdar et aI., 2014). The PP means "little posterior bridge" in latin (Geist et al.; 2014; Sharma et al, 2010; Chitroda et al, 2013; Saokar & Nawale, 2014; Cho, 2009; Mudit et al, 2014). PP manifests as a partial or complete bony arch/bridge in the atlas vertebra (Perez et al., 2014). In the literature, there are many terms that describe this anomaly (Table I), however, its most accepted name is PP (Baba et al., 2015).

Complete ossification of atlanto-occipital membrane leads to arcuate foramen, which may cause external pressure on the vertebral artery, especially during extreme rotatory movements of the head (Unur et al., 2004). The potential clinical significance of PP is controversial because the majority of patients with this finding are asymptomatic (Mudit et al., Chitroda et al.) but this bony arch may be linked to different symptoms, ranging from neckache to headache and migraine and it may also be incorrectly assessed during orthopedic surgery for fixation of atlas-axis, with consequent risk of damaging the vertebral artery (Chitroda et al.). It is important for the anatomist, radiologist, neurophysicians and neurosurgeons who are dealing with this region. Most prevalence studies had been performed by plain radiographs or dried atlas specimens (Cho). Because of the anomaly can be seen complete or incomplete there is a disagreement about the frequency of complete and incomplete cases (Geist et al.). The prevalence of this anomaly in the literature varies widely, with reports ranging from 4.3 % (Sharma et al.) - 68 % (Baba et al.).

The centre of sella turcica is routinely used as a cephalometric landmark to act as a reference point, S, for evaluating spatial position of both jaws as they relate to the cranial base. Anatomically sella turcica is a saddle-shaped depression in sphenoid bone which contains the pituitary gland (Shah et al., 2014). It consists four clinoid processes (two anterior and two posterior), the anterior border represented by tuberculum sellae and the posterior border by the dorsum sellae (Kucia et al., 2014). On a lateral cephalometric radiograph the image of sella turcica is U shaped (Shah et al.), it may be concave, flat or even convex (Kucia et al.). A deviation from normal size and shape of sella turcica can be an indication of a pathological condition of the gland (Shah et al.). Investigations concerning the sella turcica have not only focused on size but also on morphology. A normal morphological variation of sella turcica must be considered as it may vary greatly from individual to individual (Shah et al.; Nagaraj et al., 2015). The most frequent abnormality described in the orthodontic literature is sella turcica bridge (STB) (Kucia et al.). The fusion of anterior and posterior clinoid processes or a calcification of interclinoid ligament termed as STB (Shah et al., Kucia et al.). This osseous structure has been termed differently in the literature (Table II). The prevalence of STB or calcification of the interclinoid ligaments was reported in the literature between 1.1 % (Alkofide, 2007)--18.6 % (Becktor et al., 2000).

Recently some studies have been done to establish connection of craniofacial skeletal anomalies with dental anomalies. It appears that tooth formation and tooth eruption and sella turcica bridging, as well as neck and shoulder skeletal development, are influenced by neural crest cells (Saokar & Nawale). Our purpose in this study is to find out association between STB and PP.

MATERIAL AND METHOD

After local institutional research ethics committee approval (no.#2016.003), radiographs were retrieved from the archived records of Necmettin Erbakan University Faculty of Dentistry, Konya, Turkey. Orthodontic records, digital panoramic radiographs and digital lateral cephalograms from 752 patients, comprising 376 males and 376 females, within two age subgroups (9-15 and 16-24) were examined. The average age was 14.9-year-old (range 9-24 years). The distribution of the sample by age was presented in Table III.

Digital lateral cephalometric radiographs were obtained in standart position by using J MORITA (2D Veraviewpocs, MFG corp, Kyoto, Japan) machine with a tube voltage of 65 kV, tube current of 10 mA and exposure time of 4.9 s. The images were analyzed in a Dell Precision T7600 workstation (Dell, Round Rock, TX) using a 32-in Dell LCD screen with a resolution of 1280x1024 pixels in JPEG (Joint Photographic Experts Group) format.

Inclusion criteria

1. Healthy patients without any history of systemic diseases and long term use of drugs.

2. Patients in the age group of 9-24 years.

3. Patients advised for lateral cephalometric radiographs for orthodontic treatment.

4. High-quality radiographs which were taken by trained radiographic technicians in a standardized manner.

Exclusion criteria

1. Individuals with congenital defects in the craniofacial region like clefts and malformations

2. History of cranifacial fractures

3. Patients suffering from disorders of bone, nutritional deficiencies and endocrinal disturbances.

Each radiograph was carefully inspected for the presence of a STB and a PP, whether it was complete or partial (Fig. 1). Because we inspected neutral lateral radiograph only, we were not able to determine if the anomaly was uni or bilateral (Perez et al., 2014). Direct visual method of examination under adequate illumination was used. During initial examination all lateral cephalograms were observed by a radiologist and an orthodontist (MT and HK). To eliminate any error 100 randomly selected lateral cephalograms were re-examined separately by the same two authors 1 month after initial examination. There was almost perfect agreement between the two authors and the two examinations.

Shape and morphological appearance of sella turcica were assessed according to the method described by Axelsson et al. (2004) (Fig. 2). Orthodontic classification was carried out using Steiner analysis. Based upon the ANB angle, subjects were classified into Class I, II and III. ANB angle of [+ or -]2 belongs to Class I skeletal base. ANB angle>4 belongs to Class II skeletal base and ANB angle<0 belongs to Class III skeletal base (Fig. 3).

A chi-square test was used to find out the association of STB and PP. All statistical analyses were performed using SPSS 21.0 (Statistical package for social science Inc. Chicago, USA).

RESULTS AND DISCUSSION

The morphology of sella turcica appeared to be normal in shape 30.7 % of subjects, regardless of sex, age, or skeletal type (Table IV). Table V shows the distribution of skeletal classes of patients. The majority of subjects were in class II. There was no statistically significant difference between skeletal classes and sella turcica bridging (p>0.05).

The prevalence of incomplete and complete calcification of PP were given in Table VI. No statistically significant association were observed between skeletal classes and PP (p>0.05).

STB and PP prevalence were increased by aging (Table VII). Although there was statistically significant association between age and sella bridging, there was no statistically difference between age and PP. No statistically significant association were observed between sex and PP, sex and sella bridging.

Although males had higher values of prevalence, no statistically significant association were observed between sex and PP, sex and sella bridging

(Table VIII).

The prevalence of incomplete, complete PP and STB was 14.8 %, 10.5 % and 24.2 %, respectively. There was statistically significant association between STB and PP (p<0.001). PP was found to be present more in the subjects with sella bridging compared to subjects without bridging (Table IX).

The prevalence of PP was increased in patients with palatally displaced canines (PDC) (p<0.05) but there was no statistically significant differences were observed between sella bridging and PDC (p>0.05) (Table X).

DISCUSSION

The lateral cephalograph is the most common diagnostic radiograph used in clinical orthodontics (Mudit et al., Sharma et al.). They are used to evaluate the craniofacial and dental structures, but they also include other diagnostics information about the skull, face and upper cervical spine, and various occult pathologies and rare normal variants involving the head or spine (Perez et al., 2013). Identifying the affected side of atlas is very difficult with lateral radiographic views because the presentation of PP can be uni or bilateral. The exact characterization is possible only by three dimensional (3D) computed tomography (CT) reconstruction (Perez et al., 2014). Additionaly cone beam CT (CBCT) has great advantages over planar skull radiography in visualizing the cervical vertebrae. CBCT provides demonstration of the vertebral column in three planes of space, thereby providing the benefits of conventional CT with generally lower radiation exposure and greater spatial resolution (Geist et al.). Plain film radiographs are useful to indicate the presence of PP; but the detection of the osseous bridges on plain film radiographs depends on the thickness of the bridge, a fine thread of ossification may be difficult to detect and thinner bridges are detected using 3D CT scanning only (Perez et al., 2014). Cho, compared 3D CT scans against plain film radiography and found statistically significant differences in the frequencies of the two types of radiographic studies influenced by the different diagnostic values of CT scans contrasted with the plain film radiography.

Autopsy studies have reported lower rates of STB compared with the higher rates found in radiographic studies. The differences between direct anatomical studies and data from lateral cephalometric radiographs have been attributed to superimposition of the overlapping clinoid processes of the sella turcica (Abdel-Kader, 2007). For this reason, only three dimensional imaging such as CT or CBCT could give more precise information about the sella area. However, routine use of these imaging techniques in patients is not advised due to the higher exposure to radiation, particularly with CT.

In this investigation, the overall prevalence of complete and incomplete PP was 25.3 %, similar to the results of some researchers (Geist et al.; Perez et al.; 2014). Other authors, however, have reported a smaller percentage of PP (Unur et al.; Sharma et al.). The prevalence of PP has been reported to be between 4.3 % (Sharma et al.) and 68 % (Baba et al.). Researchs in the literature represent many different ethnic and racial groups, which may explain the wide range of prevalence (Geist et al.). Mudit et al., suggested that ethnicity could change the prevalence of this entity. Standardization and disagreement between observers are anohter problems, making comparisons between reports difficult (Geist et al.). There are also many factors determining the visibility of PP in radiographic images such as film processing and proper selection of kVp and mAs.

We found increasing percentages of PP from the youngest to the oldest age group in accordance with Geist et al. This suggests that PP bridges may form more frequently after puberty (Geist et al.). Various theories have been put forward by different researchers for the origin of the bridges leading to the foramen formation. The mechanism of formation is not clearly understood and a subject of much debate but a number of theories have been put forward including (Tubbs et al., 2007): a genetic trait, a remnant manifestation of an occipital vertebra, the result of external mechanical factors such as carrying heavy objects on the head, an ossification related with increasing age, and the activation of a special osteogenic potency existent in the craniocervical junction region in the connective tissue surrounding the vertebral artery possibly induced by the pulsation of the vertebral artery.

This study found a higher percentage of males with PP but there is no consensus regarding the prevalence of PP in males compared with females (Geist et al.). The frequency of PP increased in subjects with palatally displaced canines in accordance with Leonardi et al. (2009). It may act as a useful diagnostic predictor of susceptibility to local dental problems.

The prevalence of STB shows great variation among different populations between 1.1 % (Alkofide)-18.6 % (Becktor et al.). According to our results STB (24.2 %) are not so infrequent radiographic findings in Turkish orthodontic patients. The prevalence of STB was higher in the older age group in the present study but it also could be seen in the younger age group. Formation of the STB may result directly from the pattern of sphenoid development or can be dictated by the physiological activities of chemical compounds that are involved in embryogenesis and build up of the bones (Skrzat et al., 2006).

There was a clear tendency towards a greater frequency of a STB in patients with severe craniofacial deviations (Becktor et al.). The morphological variations of sella turcica with greater severity are more commonly seen in syndromic patients such as Down's syndrome, William's syndrome and Seckel syndrome (Nagaraj et al.). The occurence of STB has been described as a radiographic feature in basal cell carcinoma (Gorlin-Goltz) syndrome, Rieger syndrome, Axenfeld-Rieger syndrome and other disorders and syndromes. Sellar bridges were demonstrated radiographically to a 25 % extent in idiots, to 20 % in criminals, to 15 % in epileptics, and to 38 % in other cases with mental disorders (Kolagi et al., 2011).

The interclinoid ligament bisects the wall of the cavernous sinus, dividing it into two triangles; carotid trigone anteromedially and occulomotor trigone posterolaterally. Thus ossification of this ligament may influence such structures as the internal carotid artery or the occulomotor nerve. Anomalies of sellar region may create difficulty in the regional surgery planning. Removing the anterior clinoid process is an important step in exposing the structures in the cavernous sinus and is highly complicated due to the neuronal and vascular realtionships. The presence of ossified interclinoid ligament makes the removal of anterior clinoid process more difficult and increases the risks especially in the presence of aneurysm (Kolagi et al.).

Our results indicated that there was a statistically significant association between STB and PP. This relationship may be based on the involvement of neural crest cells and/or homeobox or hox genes during the developmental stage (Saokar & Nawale). Our results in contrast with Leonardi et al. They did not found any relationship between STB and PP, but we are in accordance with the study done by MacRae (1953) and Saokar & Nawale. Mac Rae found out the different variants of atlas could be accompanied by other defects within the vertebral column, such as deformation of the skull base, particularly within the Turkish saddle, extended styloid process or cervical ribs. Saokar & Nawale observed that the incidence of PP was to be more in the group with sella bridging as compared to the group without bridging.

It appears that tooth formation and their eruption and sella turcica bridge calcification, as well as neck and shoulder skeletal development, are all influenced by neural crest cells. Because the teeth, the head, and the cervical spine are influenced in their development by neural crest cells, it is reasonable to assume that any disturbance of neural crest cells might interfere with the development of one or more systems that are under their influence (Leonardi et al.)

Sekerci et al. (2015) suggested that there was a significant relationship between the presence of PP and elongated styloid process. According to our study there was a significant association between STB and PP. Based on these results future researchs into the molecular basis of craniofacial and skeletal abnormalities could benefit from the reporting of new clinical interrelationships such as those presented here (Leonardi et al.).

In conclusion this study suggests that there is a significant correlation between the presence of PP and STB. Bearing this in mind, our findings should widen the idea somewhat that PP is seen only in conjunction with STB or other skull and skeletal anomalies. If PP and STB are associated with other clinically and radiologically discernible features that often occur together and could be regard as part of a syndrome.

REFERENCES

Alkofide, E. A. The shape and size of the sella turcica in skeletal Class I, Class II, and Class III Saudi subjects. Eur. J. Orthod., 29(5):457-63, 2007.

Axelsson, S.; Storhaug, K. & Kjaer, I. Post-natal size and morphology of the sella turcica. Longitudinal cephalometric standards for Norwegians between 6 and 21 years of age. Eur. J. Orthod., 26(6):597-604, 2004.

Baba, I. A.; Shah, A. F.; Yousuf, A.; Adhnan, M. F.; Manzoor, H. & Safdar, Z. Prevalence of Ponticulus Posticus in Kashmiri population. Ann. Dent. Spec., 3(1):6-8, 2015.

Bayrakdar, I. S.; Miloglu, O.; Altun, O.; Gumussoy, I.; Durna, D. & Yilmaz, A. B. Cone beam computed tomography imaging of PonticulusPosticus prevalence, characteristics, and a review of the literature. Oral Surg. Oral Med. Oral Pathol. Oral Radiol., 118(6):e210-9, 2014.

Becktor, J. P.; Einersen, S. & Kjaer, I. A sella turcica bridge in subjects with severe craniofacial deviations. Eur. J. Orthod., 22(1):69-74, 2000.

Chitroda, P. K.; Katti, G.; Baba, I. A.; Najmudin, M.; Ghali, S. R.; Kalmath, B. & Vijay, G. Ponticulus Posticus on the posterior arch of atlas, prevalence analysis in symptomatic and asymptomatic patients of Gulbargapopulation. J. Clin. Diagn. Res., 7(12):3044-7, 2013.

Cho, Y. J. Radiological analysis of Ponticulus Posticus in Koreans. Yonsei Med. J., 50(1):45-9, 2009.

Erturk, M.; Kayalioglu, G. & Govsa, F. Anatomy of the clinoidal region with special emphasis on the caroticoclinoid foramen and interclinoid osseous bridge in a recent Turkish population. Neurosurg. Rev., 27(1):226, 2004.

Geist, J. R.; Geist, S. M. & Lin, L. M. A cone beam CT investigation of Ponticulus Posticus and lateralis in children and adolescents. Dentomaxillofac. Radiol., 43(5):20130451, 2014.

Kolagi, S.; Herur, A.; Patil, G. & Rairam, G. B. Complete sella turcica bridges prevalence and dimensions. J. Anat. Soc. India, 60(1):22-5, 2011.

Kucia, A.; Jankowski, T.; Siewniak, M.; Janiszewska-Olszowska, J.; Grocholewicz, K.; Szych, Z. & Wilk, G. Sella turcica anomalies on lateral cephalometric radiographs of Polish children. Dentomaxillofac. Radiol., 43(8):2014065, 2014.

Leonardi, R.; Barbato, E.; Vichi, M. & Caltabiano, M. Skeletal anomalies and normal variants in patients with palatally displaced canines. Angle Orthod., 79(4):727-32, 2009.

MacRae, D. L. Bony abnormalities in the region of the foramen magnum: correlation of the anatomic and neurologic findings. Acta Radiol., 40(23):335-54, 1953.

Mudit, G.; Srinivas, K. & Satheesha B. H., R. Retrospective analysis of Ponticulus Posticus in Indian orthodontic patients-a lateral cephalometric study. Ethiop. J. Health Sci., 24(4):285-90, 2014.

Nagaraj, T.; Shruthi, R.; James, L.; Keerthi, I.; Balraj, L. & Goswami, R. D. The size and morphology of sella turcica: A lateral cephalometric study. J. Med. Radiol. Pathol. Surg., 1(3):3-7, 2015.

Perez, I. E.; Chavez, A. K. & Ponce, D. Frequency of sella turcica bridge and clinoid enlargement in lateral cephalometric plain film radiography from Peruvians. Int. J. Morphol., 31(2):373-7, 2013.

Perez, I. E.; Chavez, A. K. & Ponce, D. Frequency of Ponticulus Posticus in lateral cephalometric radiography of Peruvian patients. Int. J. Morphol., 32(1):54-60, 2014.

Saokar, P. C. & Nawale, S. Radiographic correlative study of Ponticulus Posticus in dental patients. Indian J. Appl. Res., 4(5):503-5, 2014.

Sekerci, A. E.; Soylu, E.; Arikan, M. P. & Aglarci, O. S. Is there a relationship between the presence of Ponticulus Posticus and elongated styloid process? Clin. Imaging, 39(2):220-4, 2015.

Shah, A. M.; Bashir, U. & Ilyas, T. The shape and size of the sella turcica in skeletal class I, II & III in patients presenting at Islamic International Dental Hospital, Islamabad. Pak. Oral Dent. J., 31(1):104-10, 2011.

Sharma, V.; Chaudhary, D. & Mitra, R. Prevalence of Ponticulus Posticus in Indian orthodontic patients. Dentomaxillofac. Radiol., 39(5):277-83, 2010.

Skrzat, J.; Szewczyk, R. & Walocha, J. The ossified interclinoid ligament. Folia Morphol. (Wrsz.), 65(3):242-5, 2006.

Tubbs, R. S.; Johnson, P. C.; Shoja, M. M.; Loukas, M. & Oakes, W. J. Foramen arcuale: anatomical study and review of the literature. J. Neurosurg. Spine, 6(1):31-4, 2007.

Unur, E.; Erdog"an, N.; Ulger, H.; Ekinci, N. & Omer, O. Radiographic incidence of complete arcuate foramen in Turkish population. Erciyes Med. J., 26(2):50-4, 2004.

<ADD> Corresponding Author: Melek Tassoker Necmettin Erbakan University Faculty of Dentistry Department of Oral and Maxillofacial Radiology, 42050 Konya TURKEY E-mail: dishekmelek@gmail.com Received: 01-07-2016 Accepted: 26-12-2016 </ADD>

Melek Tassoker (1); Hatice Kok (2) & Sevgi Ozcan (1)

(1) Department of Oral and Maxillofacial Radiology, Faculty of Dentistry, Necmettin Erbakan University, Konya, Turkey.

(2) Department of Orthodontics, Faculty of Dentistry, Necmettin Erbakan University, Konya, Turkey.

Caption: Fig. 1. Incomplete and complete form of PP.

Caption: Fig. 2. Different morphological types of sella turcica according to Axelson et al: (a) normal sella turcica, (b) oblique anterior wall, (c) sella turcica bridge, (d) double contour of floor, (e) irregular dorsum sellae, (f) pyramidal shape.

Caption: Fig. 3. Scheme used to determine the skeletal classes as for cephalometric measurements: Steiner's ANB angle on standart lateral cephalometric radiograph. OP= occlusal plane, N= nasion, A= subspinale and B= supramentale.
Table I. Various names used to describe the
ponticulus posticus (PP).

NOMENCLATURE VARIATION FOR PP

Arcuate foramen
Atlas bridging
Canalis arteriae vertebralis
Foramen arcuale
Foramen atlantoideum
Foramen retroarticular
Foramen sagittale
Kimmerle anomaly
Kimmerle deformity
Kimmerle variant
Pons posticus
Posterior atlantoid foramen
Posterior glenoid process
Posterior glenoid spiculum
Posterior ponticulus
Retroarticular ring
Retrocondylar bony foramen

Table II. Various names used to describe the sella turcica
bridge.

Nomenclature Variation for STB

interclinoid taenia

interclinoid bars

interclinoid osseous bridge

sella turcica bridge/bridging

sella bridge

roofing / bulging / calcification of the diaphragma sellae

calcified / ossified interclinoid ligament

Table III. Age distribution of the patient sample.

Age class (y)    N     Percent (%)

    9-15        452       60.1
    16-24       300       39.9
    Total       752       100.0

Table IV. Distribution of sella turcica type.

       Sella type          Frequency     Percentage (%)

Normal sella turcica          231             30.7
Oblique anterior wall          62             8.2
Sella turcica bridge          182             24.2
Double contour of floor        22             2.9
Irregular dorsum sellae       122             16.2
Pyramidal shape               133             17.7
Total                         752            100.0

Table V. Subjects grouped according to skeletal class.

Skeletal class    Frequency   Percentage (%)

       I             231           30.7
      II             411           54.7
      III            110           14.6
     Total           752          100.0

Table VI. PP distribution among patients.

PP            N     Percentage (%)

Normal       562         74.7
Incomplete   111         14.8
Complete      79         10.5
Total        752         100.0

Table VII. Association between sex and PP,
sex and sella bridging (* significant).

Age (y)           Prevalence

          Sella Bridging     PP

9-15           20 %          23%
16-24          30 %          28%
p value       0.001*        0.307

Table VIII. Associaton between sex and PP, sex and
sella bridging.

Sex                Prevalence

          Sella Bridging     PP

Female          23%          21%
Male            24%          28%
p value        0.466        0.076

Table IX. Association between STB and PP (* significant).

Patients                      PP            Total   p-value
                Present (N)    Absent (N)

With sella           78           104        182    0.000 *
bridging
Without sella       112           458        570
bridging
Total               190           562        752

Table X. Association between PDC and sella bridging, PDC and
PP (* significant)

Patients                Prevalence

               Sella bridging (%)   PP (%)

With PDC               26             29
Without PDC            25             25
p value              0.171          0.040 *

Table XI. The prevalence of PP as reported in the literature.

Authors             Year   Sample size   Review source

Unur et al.         2004       351       Lateral spine radiographs
Sharma et al.       2009       228       Lateral cephalographs
Chitroda et al.     2013       500       Lateral cephalographs
Bayrakdar et al.    2014       730       CBCT
Perez et al.        2014      1056       Lateral cephalographs
Geist et al.        2014       576       CBCT
Baba et al.         2015      1000       Lateral cephalographs
Present study       2016       752       Lateral cephalographs

Authors             Prevalence (%)

Unur et al.              5.1
Sharma et al.            4.3
Chitroda et al.           60
Bayrakdar et al.         17.4
Perez et al.            19.79
Geist et al.             26.2
Baba et al.               68
Present study            25.3

Table XII. The prevalence of sella bridging in the literature

Author            Year   Sample Size-Source           Prevalence (%)

Becktor et al.    2000   177-Lateral cephalometrics        18.6
Erturk et al.     2004   119-Dry skull                     8.18
Alkofide.         2007   180-Lateral cephalometrics        1.1
Kolagi et al.     2011   112-Dry skull                     8.04
Perez et al.      2013   417-Lateral cephalometrics        4.31
Nagaraj et al.    2015   200-Lateral cephalometrics        7.5
Present study     2016   752-Lateral cephalometrics        24.2
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Author:Tassoker, Melek; Kok, Hatice; Ozcan, Sevgi
Publication:International Journal of Morphology
Date:Mar 1, 2017
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