|Year : 2016 | Volume
| Issue : 3 | Page : 107-111
Anatomical assessment of foramen tympanicum using cone beam computed tomography images
Parastoo Afghari1, Roshanak Ghaffari1, Saeed Sohilipour2
1 Department of Oral and Maxillofacial Radiology, Dental Faculty, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran
2 Department of Otolaryngology, Isfahan University of Medical Sciences, Isfahan, Iran
|Date of Web Publication||14-Sep-2016|
Department of Oral and Maxillofacial Radiology, Dental Faculty, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan
Source of Support: None, Conflict of Interest: None
Introduction: Foramen tympanicum is a normal variation of tympanic plate of the temporal bone which exists in the tympanic plate at birth time and will rarely remain open through adulthood. The aim of this research study is to assess the prevalence of this foramen in people over 6 years of age. Materials and Methods: In this descriptive-analytic planned cross-sectional study, cone beam computed tomography (CBCT) images of 159 patients (318 ears) over 6 in the Isfahan Province during 2015-2016 were evaluated. The foramen was detected in the axial plane and then was confirmed on the other planes. On each image, the location, size, and configuration of the foramen were studied. Patients were asked about the symptoms in case the foramen was detected. Finally, the data were analyzed using the Chi-square test, independent t-test, McNemar, Fisher, and Pearson correlation coefficient (P > 0.05). Results: A total of 159 images of the patients aged 6-78 years including 99 males and 60 females were studied, of which 11 patients (6.9%) had at least the foramen on one side. The foramen prevalence was symmetrical on both sides (5%), but the tympanic plate's thinning was significantly higher on the right side (11.3%) than on the left side (5.7%) (P = 0.04). The general shape of the foramen seemed to be oval when axial and sagittal diameters were compared. Statistical analysis indicated a negative correlation between patients' age and the foramen diameter (P = 0.03, r = −0.324). Conclusion: Using high-resolution CBCT images, the prevalence of the foramen tympanicum in people over 6 in Isfahan was found to be 6.9% and symmetrical in the two sides and in both genders.
Keywords: Cone beam computed tomography, external ear canal, foramen tympanicum, temporomandibular joint
|How to cite this article:|
Afghari P, Ghaffari R, Sohilipour S. Anatomical assessment of foramen tympanicum using cone beam computed tomography images. Dent Hypotheses 2016;7:107-11
| Introduction|| |
Foramen tympanicum (also called, foramen of Hushke) is referred to a normal variation in tympanic plate of temporal bone in the human skull which gradually closes before the age of five. In rare cases, however, it persists permanently until older ages. This phenomenon makes the person prone to ear and temporomandibular joint (TMJ) pathology which includes salivary discharge into the ear during mastication. ,, TMJ herniation into the external acoustic canal (EAC), , infection and/or tumor spread from the EAC or TMJ to infratemproal fossa, and vice versa  and higher risk of TMJ arthroscopy complications. ,
The reported prevalence of the foramen tympanicum shows a wide range from 0.6% to 46% using different modalities. ,,, A study conducted on human skull reported the prevalence of 7%,  whereas other studies performed with computed tomography (CT) and cone beam CT (CBCT) reported different prevalence percentages from 4.6% to 46%, respectively. ,,,,
Several studies and case reports have been conducted in the literature to detect foramen tympanicum including direct observations by the use of the human skull, , conventional imaging systems (e.g., panoramic imaging, submentovertex, and linear tomography)  and most recently, CT  and CBCT. , One of the modalities that have been used in the literature is CBCT which is a new technique which uses cone beam of X-ray rotating around the patient to create the image of the body. CBCT scanners provide much lower radiation doses, higher spatial resolution, and similar or even fewer metal induced artifacts compared to the conventional CT. ,, Although these characteristics create a potential for the CBCT technique to be used as a safe modality to detect foramen tympanicum, this technique has not been used vastly among fractionates. On the other hand, since the population race might affect the prevalence of foramen tympanicum. This study was conducted to investigate the prevalence, location, and size of the foramen tympanicum using CBCT images in a particular study population in Isfahan, Iran.
| Materials and Methods|| |
In this descriptive-analytic study, CBCT images of 318 sites in 159 patients who had been referred to the radiology clinic (for different diagnostic purposes) were analyzed. The sample included 60 females and 99 males who were all over 6 years of age (from 6 to 78 years old) and all were from Isfahan, Iran. Those patients who had visible syndrome disorders, history of ear surgery, any trauma or fracture in the temporal bone were excluded from the study. Furthermore, only high-quality scans were utilized out of all images taken at the clinic. All images were taken using a digital system (Soredex-Scanora 3D-Finalnd, Tuusula, Finland), and using flat panel complementary metal oxide semiconductor with high resolution and a voxel size of 0.25 mm. Radiographic parameters were set as in the following: 90 kVp, 12.5 mA, and 4.5 s with the field of view (FOV) of 130 mm × 145 mm. The FOV was selected in a way that both TMJ and EAC were clearly visible on the image. Finally, images were all investigated by an oral and maxillofacial radiologist via the Ondemand 3D (Version 1, CyberMed Co., Seoul, Korea) software on personal laptop (Dell 420 Precision, with Windows NT).
The image of each patient was reconstructed in three planes, namely, axial, sagittal, and coronal. Foramen tympanicum detection was first achieved on axial images and then confirmed on sagittal and coronal reconstructed images [Figure 1].
|Figure 1: The foramen tympanicum in (a) axial (b) sagittal and (c) coronal planes|
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In the case of foramen presence, the patients were asked about any symptom in their TMJ or ear. The location (unilateral/bilateral) and the diameter of foramen with the accuracy of 0.01 mm in all planes were assessed across male and females as well as patients' side (right and left) [Figure 2].
|Figure 2: Measurements done in the foramen tympanicum in (a) axial (b) sagittal and (c) coronal planes|
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Moreover, the foramen morphology was assessed through comparing axial and sagittal diameters. In other cases with the absence of the foramen, the thickness of tympanic plate was reported only if it was thinner than 1 mm.
SPSS software (version 12.0.1; SPSS, Inc., Chicago, IL, USA) was used to analyze the data). The Fisher's exact test was used to compare the foramen prevalence between males and females. The McNemar test was used to assess the prevalence of tympanic plate thinning between the two sides. The Chi-square test was used to compare the prevalence of the right and left prevalence between males and females. The independent t-test was used to compare the means of age between patients with or without foramen. Finally, the paired t-test was used to compare the means of foramen diameter between the right and the left sides. A confidence interval of 95% was set for the significance of differences (differences were considered statistically significant if their associated P < 0.05).
| Results|| |
[Table 1] illustrates the prevalence distribution according to sex, involved side (right or left), and location (unilateral/bilateral). As for the total prevalence, it was found that 11 (6.9%) out of 159 patients had foramen tympanicum at least on one side (right or left). In such cases, the prevalence of foramen was equal (5%) for the right and left sides. As for the prevalence of thin tympanic plate, the McNemar test showed that 20 (12.57%) out of 159 patients had thin plates which was found to be significantly higher on the right side (11.3%) than the left side (5.7%) with the P = 0.04. The Fisher's exact test showed that the prevalence of the foramen was significantly higher in females (11.7%) than in men (4%) with a P = 0.03.
|Table 1: Foramen prevalence distribution according to sex, involved side and location|
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The Chi-square test showed that the foramen prevalence was significantly higher in females on the left side (P = 0.03), whereas the prevalence of thin plate on the same side was not significantly different between males and females (P = 0.84) [Table 2]. On the right side, however, the prevalence of thin plate was significantly higher in females than in males (P = 0.01), whereas the prevalence of the foramen was not significantly different among males and females (P = 0.46). Finally, the Chi-square test showed that the prevalence of both unilateral and bilateral foramen were significantly higher in females than in males with the values of P = 0.03 and 0.04, respectively.
|Table 2: Prevalence distribution of tympanic plate according to sex separated by involved side and locations|
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The independent t-test showed that there is no significant difference between the age means of patients with foramen (37 ± 16.3) and patients without foramen (37 ± 14.2) (P = 0.96). In other words, there was no significant relationship between age and the foramen prevalence.
Although the mean diameter of the foramen in the axial and sagittal planes was slightly more on the left side, the paired t-test showed no statistically significant difference in the mean diameter of the foramen between left and right sides (P = 0.28). Yet, the mean sagittal diameter of the foramen was found to be higher than the mean of the axial diameter.
According to the assessment results, sagittal and axial diameters of the foramen in females were higher on the right side, whereas in males it was the opposite of it. However, statistical comparison of such findings was not achievable due to the low sample size of patients with foramen. Finally, the Pearson correlation coefficient showed an inverse relationship between the age and the foramen diameter (r=-0.324, P=0.03).
| Discussion|| |
This paper is aimed to assess the anatomy of the foramen tympanicum using CBCT images of people over 6-year-old in a certain population in Iran. CBCT is a new technique which has been widely used in the last decade for maxillofacial imaging purposes. ,, The main advantages of this technique are in its lower radiation doses, higher spatial resolution, and lower metallic artifacts compared to the conventional CT. These advantages were the main motive for this study to make use of CBCT in detecting foramen tymapinucm.
The findings of this study showed a total prevalence of 6.9% which was lower than the reported prevalence of two other CBCT studies conducted in Turkey with the prevalence of 17.9% and 22.7%, respectively. , This difference in the foramen prevalence might be attributed to the race of the study population or the CBCT unit used. Furthermore, the total prevalence was different from other studies with the use of skull or conventional radiographic techniques. This difference might be, to some extent, due to the fragileness of the skull bone and also geometrical projection errors causing magnification and distortion in conventional imaging.
The foramen distribution according to sex and the involved side have been varied in different studies in the literature. However, the foramen prevalence in females and unilateral location were mostly higher as illustrated in the following. A study conducted in 2005 showed the prevalence of 4.6% and 1.5% for females and males, respectively, while an equal prevalence of 3.1% for both unilateral and bilateral locations.  In another study in 2009, a higher prevalence of foramen in females in their 50s was reported.  The findings of the current study indicate that unilateral and bilateral foramen prevalence was significantly higher in females (6.7% and 5%) than males (2% and 2%). This type of foramen distribution might be due to differences in growth and development of mandible in males and females and also due to the differences in the mechanical environment of ossification on the both sides of the face.
A study conducted in 2011  found that the incidence of foramen tympanicum decreases with aging. In addition, this study also found that the foramen diameter decreases by aging. Since tympanic and maxillofacial bones grow after birth primarily because of the pressure made by mastication, deglutition and respiration, , it can be hypothesized that this process may continue through adulthood and thus it can be hypothesized that the foramen tympanicum may close over time.
A study conducted in 1991 on the skull showed a mean axial diameter of 3 mm.  Another study using a high-resolution CT in 2005 showed a mean axial and sagittal diameters of 4.2 mm and 3.6 mm, respectively. Furthermore, the mean axial and sagittal diameter of the foramen were reported 5 mm and 2 mm, respectively, in a study conducted in 2012  and thus, the morphology of the canal was considered to be oval. Another study conducted via direct observation of human skull also found the ovoid and round morphology of the foramen in different cases.  The current study, however, found the mean axial and sagittal diameters to be 1.83 mm and 2.01 mm, respectively, on the right and 2.15 mm and 2.56 mm, respectively, on the left which were all less than the latter studies. Nevertheless, in accordance with the latter study, the morphology of the foramen was estimated to be ovoid.
Although most of the reported cases in the literature with foramen were asymptomatic, there exists some reported cases with clinical manifestations as in the following: In two studies conducted in 2003 and 2004, the herniation of TMJ soft tissue into the EAC and fistula formation between the parotid salivary gland and EAC was found to be correlated with the presence of foramen. , In this study, however, the researchers found no obvious symptoms among patients following the clinical examination.
| Conclusion|| |
Using high-resolution CBCT images, the prevalence of the foramen tympanicum in people over 6 in Isfahan was found to be 6.9% and symmetrical in the two sides and in both genders which can help practitioners to narrow the margin of error in diagnosis, treatment, and prognosis of ear and TMJ pathologies.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2]