The aim of this study was to determine the prevalence and characteristics of pneumatization of the glenoid fossa and articular eminence by means of cone beam computed tomography (CBCT) images. CBCT images of 658 patients (1316 joints) were evaluated to determine pneumatization in the articular eminence (PAT) and roof of the glenoid fossa (PGF). Age and gender were recorded for all patients and, for the cases of pneumatization, laterality and type (unilocular or multilocular) were noted. Its prevalence was correlated with gender, age and laterality by statistical analyses. 21.3% of individuals presented with PAT and 38.3% presented with PGF. Considering the temporomandibular joint, PAT was in 15.5% and PGF in 30.2%. Of PAT cases, 54.3% were unilateral and 45.7% bilateral; 3.4% were unilocular and 96.6% were multilocular. In the PGF cases, 42.5% were unilateral and 57.5% bilateral; 0.02% was unilocular and 99.8% were multilocular. There was no statistical difference regarding gender and age; but there was statistical difference regarding laterality, with higher frequency on the left side. In conclusion, there was a significant prevalence of PAT and PGF in the studied population; their prevalence seems higher than has been previously supposed.
The bones of the skull contain many air-filled cavities, which are referred to as pneumatization. Ten sites of air cells can be found within the temporal bone, including the zygomatic process of the temporal bone which is termed the pneumatized articular eminence (PAT) and the roof of the glenoid fossa. The term PAT was used for the first time by Tyndall and Matteson to describe air cells that occur in the root of the zygomatic arch and in the articular eminence of the temporal bone, that is, similar to air cells in the mastoid process and ethmoid bone. These authors also identified its common characteristics as: an asymptomatic radiolucent defect in the zygomatic process of the temporal bone with an appearance similar to mastoid air cells; extension of the defect anteriorly as far as the articular eminence but not beyond the zygomaticotemporal suture; and no enlargement or cortical destruction of the zygoma. Additionally, they classified the PAT as unilocular or multilocular.
Knowledge of these pneumatizations adjacent to the temporomandibular joint (TMJ) is important as they represent sites of minimal resistance and facilitate the spread of various pathologies into the joint as inflammation, tumour or fractures. Tumours of the mastoid process and ear may extend into the TMJ, while otitis or mastoiditis may involve the TMJ and can result in ankylosis. They are possible complicating factors in TMJ surgery so several authors have recommended that imaging studies should be performed prior to any surgical procedure.
Panoramic radiography is considered useful to display the PAT, for that reason many case reports and prevalence studies on PAT are based on the use of this radiography ; other conventional projections of the skull do not provide adequate visualization of the posterior aspect of the zygomatic arch. Panoramic radiographs are considered the initial method to evaluate these defects because they are obtained during routine examination of many patients; in comparison to computed tomography (CT) they are cheaper and incur a lower radiation dose. These disadvantages have been overcome now cone beam CT (CBCT) is increasingly replacing CT because it provides an adequate image quality associated with lower radiation exposure, fast scanning time, lower number of image artefacts and real time image analysis. Since CBCT does not present superimposition of images, it surpasses the diagnostic accuracy of panoramic radiographs in the evaluation of temporal air spaces.
To the authors’ knowledge, only one study of the prevalence of PAT using CBCT has been performed. The authors evaluated the prevalence in the Turkish population; they concluded it could be possible that PAT is more frequent than is perceived and suggest more prevalence studies, particularly from developing countries. The authors did not evaluate the pneumatization of the glenoid fossa (PGF), which has the same clinical importance in the spread of pathologies into the joint and as a possible complicating factor in TMJ surgery. The aim of this study was to determine the prevalence and characteristics of pneumatization of the glenoid fossa and articular eminence regarding the age, gender, laterality and type by means of CBCT images in a population in a developing country.
Materials and methods
This study used CBCT images of patients who were referred to the Oral Radiologic Clinic at FOP/UNICAMP, between February 2010 and September 2011. The examinations were required for different treatment purposes unrelated to this study. 658 patients examined in the authors’ clinic during that period met the following selection criteria and were invited to participate in this study: Caucasian patient without maxillofacial fracture history; examination required with field of view in which the right and left zygomatic arches were adequately seen. The study was approved by the Ethics Committee in Research of the State University of Campinas and written consent was obtained from each patient.
All CBCT exposures were performed by an appropriately licensed radiologist using a Classic i-CAT scanner (Imaging Sciences International Inc., Hatfield, PA, USA), operating at 120 kVp and 8 mA, 512 × 512 matrix, 14 bits grayscale and no added filtration.
The CBCT images were analyzed using the XoranCat software version 3.1.62 (Xoran Technologies, Ann Arbor, MI, USA). The contrast and brightness of the images were adjusted using the image processing tool in the software to ensure optimal visualization. The axial, coronal and sagittal images were evaluated by two oral radiologists with at least 2 years’ experience with i-CAT CBCT, under dim light conditions, independently. If a consensus could not be reached between the two examiners, another radiologist assisted them in making the decision.
The frequency of pneumatization was quantified at the articular eminence and roof of the glenoid fossa. Diagnosis of PAT on the images was made only if the characteristics described by Tyndall and Matteson were found: a radiolucent defect in the zygomatic process of the temporal bone with the appearance similar to mastoid air cells, extending anteriorly as far as the articular eminence but not beyond the zygomaticotemporal suture, with no enlargement or cortical destruction of the zygoma. If the radiolucent defect was located on the roof of the glenoid fossa, above the condyle, it was classified as PGF. The conditions were determined on both sides. The age and gender were recorded for all patients and, for the cases of pneumatization, laterality and type were also noted. The type was also classified adapted from the study by Tyndall and Matteson as unilocular or multilocular. Unilocular pneumatization was identified as a single radiolucent oval defect with well-defined bony borders, whereas multilocular pneumatization was identified as numerous radiolucent small cavities.
The statistical analyses were performed using Stata Statistics/Data Analysis version 11.0 (StataCorp, Texas, USA). The frequency of the pneumatization was correlated with gender and laterality. These correlations were determined and assessed by the χ 2 test. The statistical evaluation of relative risk of development of pneumatization in relation to age was estimated by multinomial logistic regression models. This analysis was also used to determine if there was correlation between laterality and gender. p values < 0.05 were considered statistically significant.
In the study population there were 401 females (61%) and 257 males (39%), aged between 11 and 85 years (mean 41.7 years). 1.316 TMJ regions were analyzed.
257 (39%) individuals presented some pneumatization; 134 (20.4%) had pneumatizations in both locations; 6 individuals presented only PAT and 118 only PGF. In total, 140 (21.3%) individuals presented PAT and 252 (38.3%) presented PGF.
Considering the TMJ, PAT was in 204 (15.5%) and PGF was in 397 (30.2%). The mean age of the individuals with pneumatization was 43.02 years. The youngest individual with PAT and PGF was an 11-year-old male.