Prevalence of Pneumatized Articular Tubercle Using Panoramic Radiography and Cone Beam-Computed Tomography: A Retrospective Study.

CONTEXT: In 1985, Tyndall and Matteson first described the air cells that occur in the root of zygomatic arch and in the articular eminence of the temporal bone but do not extend beyond the zygomaticotemporal suture. AIMS: The aim is to study the prevalence and patterns of pneumatized articular tubercle (PAT) retrospectively using two different imaging modalities, i.e., digital panoramic radiography and cone-beam computed tomography (CBCT). SUBJECTS AND METHODS: Total 3000 panoramic radiographs belonging to 1291 females and 1709 males and CBCT scans of 200 patients belonging to 62 females and 138 males were studied retrospectively and investigated for radiographic features of pneumatized articular tubercle.
RESULTS: Prevalence found by using panoramic radiography is 1.96% and by using CBCT is 12.5%.
CONCLUSIONS: This research scrutinizes the prevalence of pneumatized articular tubercle and establishes the prevalence of the same among the studied population, using panoramic radiography and CBCT.

Introduction

It is extremely important to have a thorough knowledge of anatomy to be able to identify pathology and formulate a differential diagnosis.

The pneumatized of articular tubercle is a lesser-known anatomical variation. Tyndall and Matteson first described it in 1985 and they also reported three cases of this rare entity and termed it as zygomatic air cell defect.[1]

Pneumatization of mastoid process of the temporal bone begins after puberty and subsequently undergoes complete pneumatization in several years. In addition, during pneumatization of mastoid process, accessory cells may develop at numerous locations in the temporal bone including root of zygomatic arch and articular eminence. These zygomatic air cells appear as well-defined radiolucent defect with no cortical destruction of the zygoma. They do not extend beyond the zygomaticotemporal suture.[123] The pneumatization can appear as a single well-defined radiolucency termed as unilocular or as radiolucency divided into small compartments by thin septae within termed as multilocular. Tyndall also termed it as “zygomatic air cell defect.”[1] Even though pneumatized of articular tubercle and zygomatic arch is a normal anatomic variation, its presence becomes significant while planning surgeries involving the articular tubercle and temporomandibular joint (TMJ) because a pneumatized articular tubercle offers less bony resistance during surgical manipulation. The presence of air cells may also facilitate the spread of infection by providing potential pathway to the depth of the bone. Orthopantomograph (OPG) is the most commonly used presurgical imaging modality. OPG provides a good visualization of the teeth, maxillary and mandibular arches, and TMJs. Pneumatized of articular tubercle can be appreciated on panoramic radiography. However, extensive superimposition of the adjacent bony structure may obscure this normal variation.[4] Cone-beam computed tomography (CBCT) which is a three-dimensional (3D) imaging modality has the advantage of low radiation exposure (compared to CT) and low cost and provides 3D visualization of anatomic structure in thin slices.[5]

The present retrospective study was undertaken to assess the prevalence of pneumatized of articular tubercle (PAT) using two different imaging modalities such as digital OPG and CBCT.

Subjects and Methods

The study was carried out in the department of oral medicine and radiology. The samples were selected from the archived data in the institute from June 2015 to June 2016.

Total 3000 digital panoramic radiographs which were free of any positioning or processing errors were selected randomly from the departmental data. Panoramic radiographs of both the genders of all age groups were included in the study. The radiographs with developmental anomalies, fractures involving mid-face region, and those with positioning error were excluded from the study. These digital panoramic radiographs were obtained using machine “Planmeca Proline EC” (Helsinki, Finland) and were viewed with “Planmeca Image Works DICOM workstation” software.

CBCT scans of 200 patients were selected from the departmental records. The scans included participants of both the genders of all the age groups.

The following selection criteria were used for selecting the scans:

CBCT scans of a minimum Field of vied (FOV) of 9 cm X16 cm covering the mid-face region

Only those scans which showed the zygomatic arches completely were selected

Only those cases which were devoid of any developmental anomalies/traumatic injuries were selected

Only those scans which were free of artifacts were selected for the study.

These scans were obtained using machine Planmeca ProMax 3D (Helsinki, Finland), and the resultant images were displayed on Samsung monitor and analyzed using Planmeca Romexis 3.2 software to visualize the zygomatic arch in multiplanar view.

Every digital panoramic radiograph and CBCT scan were analyzed by two oral and maxillofacial radiologists independently. Each observer was asked to note down the findings about the presence of pneumatized articular tubercle and its appearance.

The Pneumatized Articular Tubercle (PAT) appears as a well-defined, well-corticated radiolucency in the anterior portion of the zygomatic arch but does not destroy or expand the cortices of the zygomatic arch and does not extend beyond the zygomaticotemporal suture.[1]

The Tyndall and Matteson[1] description of PAT was used as a guideline for classifying PAT as unilocular or multilocular.

Unilocular type appears as a single round-to-oval-shaped radiolucency

Multilocular type appears as a multilocular radiolucency showing numerous small cavities resembles like honeycomb.

This study was carried out with the basic aim for ascertaining the prevalence of PAT and not to study efficacy of panoramic radiography and CBCT in the detection of PAT. The cases where there was a difference of opinion between two observers regarding the presence or absence of pneumatized articular tubercle (PAT) were excluded in the study.

The data were subjected to statistical analysis. The Cohen's kappa (k) test was applied to measured inter-observer reliability, and the Chi-square test was applied to the data to assess for statistical significance.

Results

Panoramic radiography

Out of 3000 cases that were studied independently by two observers, in cases, there was a difference of opinion regarding the presence and absence of PAT those cases were not included while calculating the prevalence of PAT.

Out of the 3000 cases selected, 1709 were male and 1291 were female

The age of the participants ranged from 5 to 91 years with a mean age of 35.06 years

PAT was found in 59 participants which included 34 males (1.98%) and 25 females (1.46%), thus representing that the overall prevalence of PAT using panoramic radiography was 1.96%

Most of the PATs were found in patients of the age group between 15 and 34 years

Majority of the PATs were found unilaterally (66.6%) than bilaterally (33.89%) and more common on the left side

The unilocular variety (60.49%) was more commonly found than multilocular variety (27.12%). Figures 1 and 2 show examples of unilocular and multilocular appearance of PAT on panoramic radiography, respectively

Figure 1

Unilocular appearance of pneumatized articular tubercle on panoramic radiograph

Figure 2

Multilocular appearance of pneumatized articular tubercle on panoramic radiograph

It was found that there was no statistically significant difference in the prevalence of PAT among both the genders [Table 1]

Table 1

Observation for PAT found on panoramic radiography

The Cohen's kappa test was applied to study inter-observer reliability in panoramic images. The k value obtained was 0.53 indicating moderate agreement between two observers.

Cone-beam computed tomography

Out of the 200 CBCT scans analyzed, 138 scans were of males and 62 were of females

The age range of participants was 10–73 years. The mean age was 30.5 years

PAT was found in 25 cases including 8 females (12.9%) and 17 males (12.31%). The overall prevalence of PAT was found to be 12.5% on CBCT

Majority of the PATs were found within the age range of 21–30 years of age group

Majority of PATs were found unilaterally (44%) than bilaterally (56%) and more common on the left side

The multilocular variety (76%) was more common than unilocular variety (24%). Figures 3 and 4 show examples of the unilocular and multilocular appearance of PAT on CBCT, respectively

Figure 3

Unilocular appearance of pneumatized articular tubercle on cone-beam computed tomography

Figure 4

Multilocular appearance of pneumatized articular tubercle on cone-beam computed tomography

It was found that there was no statistically significant difference in the prevalence of PAT among both the genders [Table 2]

Table 2

Summary of observations for PAT found on cone.beam computed tomography

The Cohen's kappa test was applied to study inter-observer reliability in CBCT images. The k value obtained was 0.96 indicating near perfect agreement between two observers.

Discussion

The pneumatization of temporal bone is a normal physiological process. It is the extension of the pneumatization of temporal bone. The pneumatization of temporal bones can be divided into five parts; middle ear, mastoid, perilabyrinthine, petrous apex, and accessory cells that develop at numerous locations. The accessory cells include squamous, styloid, occipital, and zygomatic areas. The accessory cells in the zygomatic arch can spread pneumatization into the articular tubercle.[4567] They appear as a well-defined, well-corticated radiolucent area in the zygomatic arch and articular tubercle which do not extend beyond the zygomaticotemporal suture. Tyndall and Matteson described three patterns of PAT, namely, the unilocular, multilocular, and trabecular types. In this study, the unilocular and multilocular patterns have been studied.

A thorough knowledge about PAT is important for the surgeons and radiologists. The presence of PAT increases the risk of perforation and untoward complications during TMJ surgeries such as eminectomy and eminoplasty.[8910] The less bony resistance offered by PAT also facilitates easy spread of infection, tumors, and fractures.[10] It is also important to identify PAT as it may mimic some pathological conditions occurring in this region such as vascular malformations, aneurysmal bone cyst, eosinophilic granuloma, metastatic lesions, and earlier stages of fibrous dysplasia. All these conditions may be clinically symptomatic and show bone destruction on the radiographs in contrast to air cavities (pneumatization) in the zygomatic arch which are also asymptomatic but appear well defined, nonexpansile, and nondestructive.[111]

The PAT can be visualized on Waters' view; Towne's projection, and submentovertex and transcranial view for TMJ, but these imaging techniques do not provide adequate visualization of the posterior aspect of the zygomatic arch. Panoramic radiography is routinely prescribed and easily available imaging modality which provides adequate visualization of the zygomatic arch.[1] CBCT provides a better visualization of the mid-face region as there are no superimpositions.[12]

The present retrospective study was carried out in the same population race to find the prevalence of PAT using two different imaging modalities; panoramic radiography and CBCT.

In our study on panoramic radiograph, the age range of the cases was from 5 to 91 years with a mean age of 35.5. The PAT was more common in the age group of 15–34 years. Out of the 3000 cases studied, 59 cases showed the presence of PAT. The prevalence of PAT using OPG was found to be 1.96%. Thirty-four males (1.98%) and 25 females (1.76%) were fund to have PAT. Orhan et al. and Arora et al. in their study of PAT using OPG showed the prevalence of PAT as 1.9% and 1.94%, respectively.[1314] This is in accordance to our present study.

The unilocular variety of PAT was noted more commonly, i.e., 70.68% than the multilocular type. Most of the PATs were found to be unilateral, i.e., 66.6%. The studies performed by Shokri et al., Orhan et al., and Arora et al. also showed a similar finding.[1415]

The cases evaluated for PAT on CBCT were of age range between 8 and 70 years. The PATs were more commonly seen in the age group between 21 and 30 years. From 200 cases, PAT was found in 25 patients accounting overall prevalence of 12.5%. The study done by Shokri et al. using CBCT found the prevalence of PAT 15.6%,[16] whereas a study by Ladeira et al. found 21.3% prevalence of PAT using CBCT as imaging modality.[10]

In the present study, bilaterally located and multilocular type of PAT was more commonly found, which is similar to study done by Miloglu et al. and Shokri et al.[1015]

In our study, 17 PATs were found in males (12.31%) and 8 PATs were found in females (12.9%). However, there was no statistically significant gender predilection noted.

High-resolution CT is considered as imaging modality of choice for the assessment of air spaces at the base of the skull.[10] Bronoosh et al. studied the PAT on a CT scan and reported 9.55% prevalence.[17]

Comparisons between the results of our study on CBCT had shown bilaterally located and multilocular type of PAT in contrast to the unilateral and unilocular type of PAT which is found on panoramic radiology [Table 3]. This finding can be related to the higher diagnostic accuracy of CBCT, as the 3D visualization helps to detect the pneumatization on the medial aspect of bone which can be hindered due to superimpositions on panoramic radiography.[10] Furthermore, Multiplanar visualization on CBCT could help to detect thin septae within the radiolucency in case of multilocular variety.

Table 3

Summary of results obtained by panoramic radiography and cone.beam computed tomography

Various studies have been published in the literature and their results have been summarized in Table 4.[16]

Table 4

Summary of the previously published studies in the literature[16]

Conclusion

It can be concluded from this study that the prevalence of PAT when observed using panoramic radiography was 1.96% and when observed using CBCT was 12.5%. In our study, it is observed that there is a considerable difference in the prevalence of pneumatized articular tubercle when CBCT is used as an imaging modality.

Although digital panoramic radiography is an easily accessible imaging modality to examine the zygomatic arch, it poses some limitations and PAT may escape from radiographic detection. On the other hand, CBCT provides an explicit view for the recognition of PAT. This emphasizes upon the utilization of CBCT which has been of great use in dentistry.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.