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ORIGINAL ARTICLE
Year : 2022 | Volume
: 28
| Issue : 3 | Page : 216-222
The new staging system for computed tomography evaluation of chronic otitis media and mastoiditis
Nguyen Nguyen, Quyen Le Ta
Department of Otolaryngology, Hue University of Medicine and Pharmacy, Hue University, Hue, Vietnam
Correspondence Address:
Prof. Nguyen Nguyen
Department of Otolaryngology, Hue University of Medicine and Pharmacy, Hue University, 06 Ngo Quyen Street, Vinh Ninh Ward, Hue City, Thua Thien Hue Province, Hue
Vietnam
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/indianjotol.indianjotol_63_22
Objective: To predict risks for complications and determine the type of operation, several studies developed the grading system based on clinical assessment. However, there is no evidence regarding the score for tomographic opacification and bone erosion of temporal bone on computed tomography (CT) scan. Therefore, the aim of this study was primarily to design a new computerized tomography staging system for the evaluation of chronic otitis media (COM) and mastoiditis. Materials and Methods: Between August 1, 2020, and December 30, 2021, 40 patients with the clinical diagnosis of COM (males and females) have received temporal bone CT scans at medical institutions. The patients were retrospectively evaluated and verified the correlation of the score of CT imaging in preoperative evaluation with the clinical picture and surgical planning. Descriptive statistics, one-way ANOVA analysis, and Spearman's correlation test were employed to evaluate the accumulated data. The P values were calculated for all tests and its outcome <0.05 was considered statistically significant. Results: There are significant correlations between the total score and the size of perforation, the type of surgical intervention, and low-frequency air-bone gap (ABG) (P < 0.05) while no correlation between the total score and high-frequency ABG was revealed. Conclusion: The abnormal landmarks of the temporal bone are presented, and scored systematically and there is an excellent way to analyze and make a decision not only in diagnosis but also in the choice of surgical intervention.
Keywords: Computed tomography, temporal bone, chronic otitis media, cholesteatoma, mastoidectomy
Chronic otitis media (COM) is described as the result of chronic inflammation in the middle ear and it is characterized by the persistent or recurrent discharge from the middle ear cavity (MEC) through the tympanic membrane (TM) perforation. According to potential damage of the middle ear ossicles, COM was considered an important cause of conductive hearing loss (CHL), especially in a developing country. The prevalence surveys of the WHO showed that 56–330 million people suffered from the draining ear involving COM. The complication of hearing impairment was estimated in about 60% of the cases (39–200 million).[1] Exposure to the risk factors may contribute to a high burden of COM, such as inadequate antibiotic treatment, environment, allergy, poor living conditions, or patient's factors (immunity, gender, and others).[2] COM is classified into two main types: tubotympanic, a mucosal disease – “safe” or “benign type” and atticoantral, an epithelial disease – “unsafe” or “dangerous type.” The classification was based on the situation of perforation and MEC inflammation. Clinically, the tubotympanic type relates to anteroinferior part of the middle ear cleft and the central perforation and its rate of complication was very low. On the other hand, the atticoantral type involved the posterosuperior part of the middle ear cleft, an attic and marginal perforation, with or without cholesteatoma, granulations, or osteitis.[3]
The primary purpose of surgery for COM is the elimination of the disease from the mastoid air cell and the tympanic cavity as well as reconstructing a TM.[4] Due to the erosion of adjacent structures in the MEC and mastoid cavity, cholesteatoma is responsible for the complications associated with COM. The destruction of the chain ossicles results in hearing loss and its expansion can cause vestibular dysfunction, facial paralysis, and intracranial complications.[5] Congenital or acquired cholesteatoma was eradicated from the temporal bone through mastoidectomy. However, recurrent draining ear and cholesteatoma recidivism after surgery was still a challenge for ear surgeons. Despite advances in surgical microscopy and instruments, being in the antibiotic era, the incidence of recidivism ranged from 15% to 61% after the canal wall up, from 0% to 13% after the canal wall down.[6] Mastoidectomy with tympanoplasty is not only to remove any residual disease from the middle ear and mastoid cavity but also to restructure the sound transmission system. On the other hand, the aim of tympanoplasty alone is the reconstruction of the TM.[7] The success of the procedures is dependent on the surgical principle and the pathological factors related to the disease. The pathological condition of the middle ear and the mastoid cavity was considered a predictor of surgical results.[8] For this purpose, categorization systems based on preoperative conditions have been developed and one of the most reliable systems is the middle ear risk index (MERI). Nevertheless, by literature review, we found no grading system of computed tomography (CT) for temporal bone.
Based on the rapid development of radiological equipment, the role of CT in otology has been significantly promoted over the last several decades. CT has become an indispensable part in the evaluation of the patients with diseases related to the temporal bone and it also was a tool to diagnose for the causes of hearing loss. The advantages of CT were not only its high sensitivity and specificity for inflammation (opacification) but also bony tissue evaluation in detail. Consequently, CT imaging can show the state of the MEC, the mastoid air cells and it can also detect the intra- and extracranial complications. The meticulous evaluation of CT imaging is an important part in preoperative assessment and treatment strategies for COM. Furthermore, the pneumatization of MEC and mastoid air cells as well as anatomic variants in CT have been identified as crucial parameters for the staging of COM, preoperative planning, and description of disease states causing the complications.[9],[10] The key landmarks used in the present study were the most significant structures in the temporal bone. For instance, the erosion of the facial canal, lateral semicircular canal (LSC), and dural plate defect (tegmen tympani, tegmen antri) were shown in the COM cases with or without cholesteatoma. The risk of developing labyrinthitis was increased by the LSC dehiscence and the erosion of tegmen tympani, tegmen antri raised the probability for development of the pathology to the brain. In addition, the preoperative assessment of the anatomy as well as anomalies of the facial nerve (tympanic and mastoid segment, especially) was crucial for preventing facial paralysis following the tympanomastoid surgery.
The aim of this study was primarily to design a new computerized tomography staging system for the evaluation of COM and mastoiditis. Furthermore, we conducted the current investigation to verify the correlation of the score of CT imaging in preoperative evaluation with clinical pictures and surgical planning.
Materials and MethodsBetween August 1, 2020, and December 30, 2021, 40 patients with the clinical diagnosis of COM (males and females) have received temporal bone CT scans at medical institutions. These patients were characterized by a chronic perforation of the TM, and persistent ear discharge. Informed consent was obtained from all the participants before conducting the study. The study protocol was conducted according to the Declaration of Helsinki rules and clearance from our corresponding Institutional Review Board was obtained before starting the study. Exclusion criteria were prior mastoidectomy, congenital malformations, trauma, and the other pathologies of the temporal bone. A radiologist was blinded to the clinical information and diagnosis, and he was invited to evaluate these CT scans. Based on the important anatomic structures in the CT scan analysis of the temporal bone, the images were assessed and scored [Table 1].[11] The temporal bone were divided into seventeen portions, including epitympanum, Prussak's space, mesotympanum, hypotympanum, protympanum, malleus, incus, aditus ad antrum, mastoid antrum, mastoid air cells, chaussé spur, tegmen tympani, tegmen antri, LSC, facial nerve canal (tympanic segment), facial nerve canal (mastoid segment). The severity of mucosal inflammation or fluid accumulation at the tympanic cavity and mastoid compartment was scored as 0 (normal), 1 (partial opacification), and 2 (complete opacification). Normally, the mastoid is divided into numerous air-filled cavities by mastoid septations. Therefore, the severity of inflammatory lesions of the mastoid cavity depended on the destruction of the bone septations, and they were scored as 0 (pneumatized), 1 (opacified/poorly pneumatized without trabecular destruction), and 2 (opacified/poorly pneumatized with trabecular destruction). In addition, inflammatory conditions with bone erosion were characteristic of malignant tumors or cholesteatoma. The destructive process of bone was scored as 0 (normal), 1 (erosion/dehiscence), or 1 (fistula) with LSC.
The CT evaluation was performed using the Siemens-somatom scope multidetector CT machine. Coronal and axial 0.75-mm slice thickness of temporal bone were used to calculate and then release a new score for the evaluation of COM and mastoiditis.
The thin transparency sheet was used to measure the size of the perforation. The sheet was drawn a graph of 1 mm × 1 mm2 size on its surface. The oval piece of sheet with 9 mm × 8 mm dimension was cut and then, it was sterilized by soaking in cidex. Before starting the further procedure, the size of the perforation was measured intraoperatively under operating endoscopy. The calculated size of perforation was compared to the total area of TM (55 mm2) and it was classified as:
<25% equivalence with 1–14 mm2 perforation25%–50% equivalence with 15–27 mm2 perforation>50% equivalence with >27 mm2 perforation.All pure-tone audiometric data were extracted from presurgery. The thresholds of air and bone conduction were recorded at the frequencies of 250, 500, 1000, 2000, 3000, 4000, and 8000 Hz. The pure-tone average was calculated by using the average thresholds at the frequencies of 500, 1000, 2000, and 3000 Hz for both air and bone conduction.[12] The difference between air conduction and bone conduction was defined as the air-bone gap (ABG). The mean of ABG at the frequencies of 250, 500, and 1000 Hz was termed low-frequency ABG. On the other hand, high-frequency ABG was termed as the frequency of 4000 Hz.
Data analysis was executed by using SPSS for Windows, version 26 (SPSS Inc., Chicago, IL, USA). The Shapiro–Wilk test was used to verify that all continuous variables designed for statistical testing were normally distributed. The comparison of the total score extracted from tomography evaluation of the temporal bone among the group of the size of perforation, type of surgical intervention, and type of hearing loss on audiogram was performed by using the one-way ANOVA analysis. Furthermore, the test was used to determine the potential relationship between the total score of tomography evaluation of the temporal bone and preoperative air-bone gap (ABG), low-frequency ABG as well as high-frequency ABG. The P values were calculated for all tests and its outcome <0.05 was considered statistically significant. Finally, Spearman's correlation coefficient was employed. All study protocols were approved by our research ethics committee (decision number H2021/151) on May 27, 2021.
ResultsA total of 40 patients have been operated for their COM diagnosis in our department. The mean age was 39.65 years and the range of age was between 9 and 74 years. Twenty-five patients (62.5%) were female and 22 (55%) were left ears. The surgical intervention included tympanoplasty alone (25%), mastoidectomy and tympanoplasty (57.5%), and radical mastoidectomy (17.5%). All tympanic perforations were classified by endoscopic measurement: 17.5% (<25% perforation), 27.5% (25%–50% perforation), 35% (>50% perforation), and 20% (attic perforation) [Table 2].
In comparison of the size of perforation with the total score of tomography evaluation of the temporal bone, the size of TM perforation <25% was obtained to have a mean total score of 6.29 (standard deviation [SD] of 4.89), the size between 25% and 50% had a mean total score of 6.73 (SD of 4.67), the size >50% had a mean total score of 9.21 (SD of 2.67), and in the attic perforation, the mean of the total score was 15.75 (SD of 4.06). The total score difference in the size of TM perforation was statistically significant, with P < 0.05 [Figure 1].
Figure 1: The box plots of the size of perforation with the total score of tomography evaluation of the temporal bone. X-axis: size of perforation; Y-axis: total score of tomography evaluation of the temporal bone. The interquartile range was represented by the boxes. The middle 50% of total score distribution, and the whiskers involve the entire range of total score. The horizontal lines divide the boxes and they represent the median. The outliers are individual dots outside the whiskersThe distribution of the type of surgical intervention with the total score of tomography evaluation of the temporal bone is graphically represented in [Figure 2]. A clear trend of increase in the total score of tomography evaluation can be appreciated. Within the type of surgery, radical mastoidectomy corresponded to the highest total scores. The P value of the ANOVA test between the type of surgery and the total score was <0.05 (statistical significance).
Figure 2: The box plots of the type of hearing loss on audiogram with the total score of tomography evaluation of the temporal bone. X-axis: the type of hearing loss on audiogram; Y-axis: total score of tomography evaluation of the temporal bone. The interquartile range was represented by the boxes. The middle 50% of total score distribution, and the whiskers involve the entire range of total score. The horizontal lines divide the boxes and they represent the median. The outliers are individual dots outside the whiskersRegarding the type of hearing loss on audiogram with the total score, the mean score was different between the groups (CHL mild = 6.13 ± 4.35 (mean ± SD), CHL moderate = 10.3 ± 5.06, CHL severe = 14.2 ± 4.03, and mixed hearing loss (MHL) moderate = 10 ± 3.08, MHL severe = 12 ± 6.08). Based on one-way ANOVA, The mean scores of the type of hearing loss were significantly increased (P < 0.05) [Figure 3].
Figure 3: The box plots of the type of surgical intervention with the total score of tomography evaluation of the temporal bone. X-axis: the type of surgical intervention; Y-axis: total score of tomography evaluation of the temporal bone). The interquartile range was represented by the boxes. The middle 50% of total score distribution], and the whiskers involve the entire range of total score. The horizontal lines divide the boxes and they represent the median. The outliers are individual dots outside the whiskersSpearman's correlation analysis was used to examine the correlation between the factors that affected the total score of tomography evaluation [Table 3],[Table 4],[Table 5]. Finally, the hearing loss grades based on four frequencies (500, 1000, 2000, and 3000 Hz) [Table 3], low-frequency [Table 4], the operative type, and size of TM perforation had a highly significant correlation with the total scores. Therefore, the worse the hearing loss grade at four frequency and low frequency was, the higher the total score was and vice versa [Table 3] and [Table 4]. Furthermore, a direct correlation between the total score and the type of surgery was shown. The highest total score corresponded to the patient with radical mastoidectomy, whereas the lowest total score was for the patient with tympanoplasty alone.
Table 3: Comparison of the mean total score of tomography evaluation of the temporal bone between the hearing loss grades
Table 4: Comparison of the mean total score of tomography evaluation of the temporal bone between the hearing loss grades at low-frequency
Table 5: Comparison of the mean total score of tomography evaluation of the temporal bone between the hearing loss grades at high-frequencyAll patients were performed with axial and coronal CT. Each anatomical structure of the temporal bone of each patient was evaluated separately in other planes. On the axial plane, we can evaluate the external auditory canal, middle ear and mastoid, inner ear, and facial nerve canal. As shown in [Figure 4]a, the tympanic cavity was opacified with complete erosion of the incus long process and the stapes while the malleus neck is intact. On the other hand, the incomplete opacification of the tympanic cavity, as well as the intact incus long process and the stapes are presented in [Figure 4]a and [Figure 5]a. On the coronal plane, the erosion of chaussé spur, tegmen tympani, tegmen antri, and the bone wrapping of the LSC was shown in the case of cholesteatoma. Furthermore, the chaussé spur and tegmen tympani are eroded in [Figure 4]b and [Figure 5]b, respectively. The two examples of audiograms from representative patients arepresented in [Figure 4]c and [Figure 5]c.
Figure 4: Computed tomography and audiogram of the clinical case was used to calculate the score. (a) Axial section showed sclerotic mastoid, total antrum opacification, incus and stapes erosion. (b) Coronal section showed opacified mesotympanum and hypotympanum. Also, the chaussé spur was eroded. (c) Representative audiogram displayed worsening ABG at four-tone average: 500, 1000, 2000, 3000 Hz on right ear. ABG: Air bone gap
Figure 5: Computed tomography and audiogram of the other clinical case. (a) Axial section showed sclerotic mastoid, incomplete antrum opacification. (b) Coronal section showed partially filled mesotympanum and total filled hypotympanum. (c) Representative audiogram displayed moderate ABG at four-tone average: 500, 1000, 2000, 3000 Hz on right ear. ABG: Air bone gap Discussion The number of COM surgical interventions in the 30s and 40s age groups (mean: 39.65) was significant [Table 2]. To explain the reasons for the dominance of the age groups, there were a few suggestions such as the young age of society, the risks of anesthesia and surgery were less than in the groups. Interestingly, the proportion of female patients was higher than men in this study, and the previous studies have reported similar results.[13],[14] It was presumed that COM was more likely to develop in females because the female's Eustachian tube More Details is shorter than men's.[15] In our study, the left ear was involved in 55% of the cases. On the other hand, the right ear was seen in 60% of the cases in the previous study.[16] The compatibility between the operative management and the proper diagnosis will result in a good outcome. In this study, the presence of inflammatory or cholesteatoma disease in the mastoid was managed with tympanomastoidectomy or radical mastoidectomy, respectively. The tympanomastoidectomy was still predominant in our study [57.5%, [Table 2]].
Several functions of the TM are known such as protection of the MEC and mastoid cavity from infections, sound transmission across the middle ear, and the important factor in the physiology of hearing. TM perforation can result in serious effects such as hearing loss, the inflammatory process of the mucosal lining in the middle ear cleft. In the previous studies, they showed that the larger the perforation TM was, the greater hearing loss was as well as the more severe the inflammation in the middle ear cleft was.[17],[18] The selected management according to the pathological condition of MEC will increase the compliance of the patients and it will also improve the result of the surgery. The staging system of temporal bone CT is used to stratify the severity of the temporal bone destruction in COM patients. The correspondence between the staging system and the size of TM perforation suggested that the patients with lower temporal bone destruction will have a small perforation and vice versa. Moreover, the highest score of the staging system was compatible with attic perforation of TM. Our findings imply that attic perforation is an event which precedes the severe damage of the anatomic structures in the temporal bone.
The damage of TM or ossicular chain resulted in CHL with altered degrees. The present study showed that the staging system of temporal bone CT was used as a tool to evaluate the prognostic value of the several pathology-induced hearing loss. The relation of the severity of CHL and the total score is clearly shown in [Figure 2]. Interestingly, 9/40 (22.5%) cases were reported with sensorineural hearing loss (SHL) in our study. Despite the various studies of the association between CSOM and SNHL, the consensus was still deficient in its importance. It was hypothesized that the inflammation in the MEC may be infiltration of inflammatory cells, metaplasia, and hyperplasia of the outer layer of the round window membrane (RWM). The changes of the RWM led to the alteration of the RWM permeability; therefore, the bacteria and their toxins would pass through the RMW and they induced irreversible damage to the inner ear function. Particularly, the vulnerable location was anatomically next to the RWM and there was the high-frequency region.[19],[20]
The outcome of surgery varied from patient to patient. One of the reasons for the success of the surgery was the type of the selected tympanoplasty. In our study, we concluded that the status of MEC and mastoid cavity structures were the determining factors for the selected tympanoplasty. As shown in [Figure 3], the tympanoplasty alone was done with the mean ± SD (2.8 ± 1.4) of the total scores that correlated with only the perforation in the TM without active middle ear infection as well as granulation tissue. The mastoidectomy with tympanoplasty was applied for all the patients with significant middle ear pathology. These patients had the mean ± SD (9.8 ± 2.4) of the total scores. With the mean ± SD score (17.1 ± 2.4), we implied that the radical mastoidectomy was performed for extensive cholesteatoma leading to the erosion of the adjacent structures. This erosion was expressed on the CT scan with the highest score.
The major causes of acquired hearing loss in COM were chronic perforation of the TM, tympanosclerosis, and ossicular discontinuity. The degree of hearing loss was decided by the site and size of the TM perforation, ossicular damage, and expansion of pathology (granulation tissue, cholesteatoma) in MEC. The larger the perforation was, the less the collector of sound energy on the TM surface was. The total TM perforation can cause a maximum ABG up to 60 dB. The TM perforation of the posterior part or near the attachment of the malleus handle and TM was considered the cause that induced more severe CHL. Granulation tissue and cholesteatoma in the MEC will inhibit ossicular mobility and their extension has significantly eroded the ossicular chain. This resulted in hearing loss at the different degrees. In our study, when independently investigating low- and high-frequency ABG, we realized that the degree of low-frequency ABG had a correlation with the total score, while this did not happen to high-frequency ABG. This could be explained that the continuity of the ossicular chain provided more benefit to hearing at low-frequency.[21] Particularly, the soft tissues of the incus-stapes complex will improve low-frequency hearing. The elastic connection between ossicular chains transmits low-frequency sounds, but it does not effectively transmit at high-frequency sounds. Therefore, the ossicular erosion and its discontinuity may lead to frequency dependence hearing loss.
Nowadays, the CT of the temporal bone was considered the the most fundamental imaging technique for assessing the important structures in the tympanic cavity and mastoid compartment as well as signs of complications. Moreover, it also served as a guide for surgical procedures. To determine the type of surgery for individual patients, the MERI has been meticulously compared and validated, while the radiologic scoring system did not receive any scrutiny. The large number of pathological changes in the cases of COM is shown in [Figure 3] and [Figure 4]. The total score has the potential to function as a research tool for detecting the relationship between the opacification of cavities, the erosion of the important structures in the temporal bone, and clinical parameters such as audiogram.
ConclusionThe computed tomographic scoring system of the temporal bone is an accurate tool for evaluating disease states and its complications in the temporal bone; it correlates strongly with clinical parameters. The abnormal landmarks of the temporal bone are presented, and scored systematically and there is an excellent way to analyze and make a decision not only in diagnosis but also in the choice of surgical intervention.
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