Can mastoid process length predict the surgical outcome of tympanoplasty with or without canal wall up mastoidectomy in adults with chronic otitis media?
Abstract
Objectives: To study the association between the mastoid process length (MPL) and surgery success when treating chronic otitis media (COM). Postoperative hearing results and the effect of eustachian tube density and performing mastoidectomy were also explored.
Settings: Tertiary referral hospital
Participants: We included 127 patients who underwent tympanoplasty with or without intact canal wall mastoidectomy.
Main outcome measures: MPL was measured on preoperative computed tomography (CT) scans. The primary outcome of this study is whether MPL is correlated with the success of tympanoplasty at 1 year after surgery. The secondary outcome is the correlation of MPL and the postoperative hearing outcomes. Our analysis used ABG as a binary outcome with cutoff > 10 dB and Gap closure as a binary outcome with cutoff >= 0 dB.
Results: Longer MPL was reversely associated with reperforation of the tympanic membrane at 1 year after surgery in patients who received tympanoplasty without mastoidectomy (odds ratio = 0.89 with 95% confidential interval: 0.79~0.99). The success rate of tympanoplasty with canal wall up mastoidectomy was higher than that of tympanoplasty alone in patients with COM. There was no significant association of MPL with postoperative ABG (odds raio = 1.0) or postoperative gap closure (odds ratio = 1.03).
Conclusions: A longer MPL was associated with a favorable surgical outcome when performing tympanoplasty without mastoidectomy. Performing canal wall up mastoidectomy in addition to tympanoplasty was associated with an improved success rate.
Keywords: outcome, tympanoplasty, chronic otitis media, mastoid process, mastoidectomy
Key points
- Mastoid process length (MPL) is related to the surgical success after tympanoplasty in patients with chronic otitis media.
- Success was significantly higher in patients who received tympanomastoidectomy than in those who received tympanoplasty only.
- The possibility of reperforation decreased by 9 ~ 12% for a unit (mm) increase in MPL.
- Reperforation decreases by 32% for a 1 mm increase of MPL in patients who received tympanoplasty only.
- Postoperative hearing outcomes were not affected by MPL.
Introduction
Surgery is indicated for patients with chronic otitis media (COM) who have not responded to medical treatment or if a cholesteatoma is evident. Tympanoplasty with or without mastoidectomy is the surgical treatment of choice for COM. The success rates of these surgeries and of other treatment techniques are widely variable in previous studies.(1, 2) Thus, there is a need to consider other factors that may affect surgical outcomes outside of the standard surgical factors. These alternative factors can be classified as patient-related and disease-related.
Patient-related factors include the preservation of a functional mastoid air cavity (MAC) while performing surgery for a patient with COM.(1-3) This MAC acts as an air reservoir that can help regulate middle ear pressure, which theoretically helps maintain the middle ear cleft aerated and prevent tympanic membrane (TM) retractions, both of which can prevent disease recurrence. Aeration also aids sound conduction by the TM and the ossicles.(4) On the other hand, a poorly pneumatized MAC has been associated with pathological ear conditions such as secretory otitis media, atelectasis of the tympanic membrane, and cholesteatoma.(5) Advice has indicated that the MAC should not be involved in the surgery of the middle ear unless cholesteatoma is evident.(6, 7) However, previous studies have recommended mastoidectomy when the mastoid part of the temporal bone is involved.(8, 9) There is also debate surrounding mastoid pneumatization and surgical outcomes. Some studies reported that the success rate of the surgery shows a positive correlation with the mastoid cavity volume.(8, 10) However, others have noted that large mastoids do not affect the outcome of the surgery at all.(11) Additionally, researchers have debated whether to maintain or eliminate the mucosa-lined mastoid cavity.(3, 12, 13) This argument can be attributed to the variable level of experience between surgeons(14) and a lack of clear predictors of surgical outcomes.
Targut et al. described a statistically significant positive correlation between MAC pneumatization and mastoid process length (MPL) in a cadaveric study.(15) MPL was first measured radiologically and then determined under a microscope after specimen dissection. Additionally, specimens with the pathological eardrum and middle ear conditions had significantly shorter MPL than those without. These findings provide the basis to describe and clinically test an objective parameter that may show an association with surgical outcomes, which can be determined preoperatively in an objective and standardized manner.
This study aimed to explore the association between MPL and surgical outcomes in patients with COM. MPL was measured on preoperative computed tomography (CT) scans of the temporal bone. The success of the surgery was determined by the absence of TM perforation at 1-year follow-up. We explored the correlation between MPL and postoperative hearing results, an association between the level of density of the eustachian tube (ET) seen on preoperative CT with MPL, and surgical outcome.
Materials and Methods
Study design
This study is a retrospective cohort study of patients who received tympanoplasty with or without mastoidectomy for COM between July 2016 and June 2018. All adult patients who had received a tympanoplasty with or without canal wall up mastoidectomy (CWUM) for COM were included in the study. Patients were excluded if they: had a follow-up period of less than 1 year, were aged <12 years, had cholesteatoma, previous ear surgery, radiotherapy to the area of head and neck, diabetes mellitus, or connective tissue disorders. The Institutional Review Board approved this study protocol.
Evaluation of the parameters
Clinical presentation, related findings of audiological assessments and CT temporal bone, and details of the surgery and follow-up visits were retrieved from patient medical records.
Perforation size was divided into two type, small and large. Large perforation was defined as a perforation more than 50% of the whole tympanic membrane.
Preoperative CT scans were reviewed to find the MPL, which was used to measure mastoid bone pneumatization. Measurements started from the lowest point of the mastoid tip and ended at the level of the tegmen mastoideum. If the tegmen had a curved slope, the mid-level between the highest and lowest tegmen level was used as the tegmen instead (16). Also, through these scans, eustachian tube density (ETD) was compared using the Hounsfield units (HU) on a specific point near to the tympanic orifice. Follow-up details were reviewed for any sign of recurrence and or need for revision surgery. TM perforation or evidence of cholesteatoma was identified through postoperative regular endoscopic examination of the tympanic membrane. Successful surgery was defined as the intact TM without perforation or retraction at 1-year post-surgical follow-up. Audiometric results before surgery and 1-year postoperatively were reviewed. According to the guidelines from the Committee on Hearing and Equilibrium (17), hearing results were reported as a postoperative air-bone gap (ABG).
Outcome measurement
The primary outcome of this study was whether MPL correlated with the success of tympanoplasty at 1 year after surgery.
The secondary outcome was the correlation between MPL and postoperative hearing outcomes. Our analysis used ABG as a binary outcome with a cutoff of >10 dB and gap closure as a binary outcome with a cutoff of >= 0 dB.
Statistical Analysis
Data are presented as numbers with percentages for categorical variables and mean values with standard deviations for continuous variables. Comparison between groups was performed using the Student’st -test for continuous variables and with Chi-square or Fisher’s exact tests for categorical variables. An association between MPL and each binary outcome was assessed using univariate and multivariate logistic regression analyses. In the multivariate analyses, the odds ratio (OR) for MPL was adjusted for one prognostic factor at a time since the observed number of events was insufficient to include all factors simultaneously. The analysis was repeated in subgroups according to canal wall-up mastoidectomy (CWUM) categorization, which showed the interaction effect between MPL and CWUM was significant (P=0.022) for the primary outcome.
A P-value of <0.05 was considered statistically significant. All analyses were performed using R version 3.6.3 (R Foundation for Statistical Computing, Vienna, Austria) and IBM SPSS version 22.
Results
3.1. Patients characteristics
We screened a total of 287 patients who had tympanoplasty with or without CWUM for COM. A total of 127 patients met the inclusion criteria, with a mean age at surgery of 52.7 years among 38 male and 89 female patients. There were 46 patients with tympanoplasty without CWUM, and 81 patients with tympanoplasty with CWUM (tympanomastoidectomy). Ossiculoplasty was performed for 37 patients (29.1%) (Table 1).
Pre- and postoperative hearing results were obtained from 107 patients; however, patients who had received ossiculoplasty (n=37) were excluded. Therefore, 72 patients were included in the final analysis.
Table 2 shows the characteristics of the patients who received tympanoplasty with or without mastoidectomy. There was a higher chance of mastoidectomy with large, anterior, or wet type perforation. E-tube density measured by CT showed more negative HU in the tympanoplasty than in the tympanoplasty and CUWM groups. Overall, there were 16 cases (12.6%) of tympanic membrane perforation at 1-year postoperative follow-up, and the success rate was 87.4%. In tympanoplasty only (n=46), the success rate was 78.3% (36 cases). The success rate was 92.6% in patients who received tympanomastoidectomy (n=75/81). Success was significantly higher in patients who received tympanomastoidectomy than in those who received tympanoplasty only (Table 2). Among the patients whose postoperative hearing outcomes were analyzed (n=72), there was no statistical difference in hearing outcomes (air-bone gap closure at 1 year after surgery) between the two groups (Table 3).
3.2. Association of MPL with the possibility of reperforation
Table 4 shows the univariate logistic analysis for the reperforation of the tympanic membrane at 1 year. The OR of MPL for the reperforation was 0.89 (95% confidential interval (CI): 0.79~0.99, p=0.050) in univariate analysis. According to the multivariate analysis adjusted with each of age, perforation site, E-tube density and CWUM, the OR ranged from 0.88 to 0.91 (95% CI: 0.77 ~ 1.03), suggesting that the possibility of reperforation decreased by 9 ~ 12% for a unit (mm) increase in MPL. In the subgroup analysis, MPL was significantly related to the possibility of reperforation in patients who received tympanoplasty only (OR=0.68, 95% CI: 0.51 ~ 0.91, p=0.009) (Table 4). The OR was 0.68, which means the reperforation decreases by 32% for a 1 mm increase of MPL in patients who received tympanoplasty only. No statistical difference was observed between any other parameters. Additionally, MPL was not associated with the possibility of reperforation in patients who had received a tympanomastoidectomy. E-tube density did not show a significant correlation with the possibility of reperforation in all patients and subgroup analyses.
3.3. Association of MPL with postoperative hearing results
Hearing outcome was determined by the air-bone gap and gap closure measured at 1 year after surgery. ABG was categorized as = <10 dB and >10 dB. Table 5 shows the univariate logistic regression analysis for the ABG >10 dB. Postoperative ABG was not significantly associated with MPL or any other parameters (OR=1.0, p=0.976). There was no statistical difference observed for any parameters in the subgroup analysis in both groups (Table 5).
E-tube density did not show a significant correlation with postoperative ABG for all patients and in the subgroup analysis.
We also analyzed the postoperative hearing outcome with gap closure. No parameters showed statistical significance when gap closure was categorized as improvement or no improvement (OR=1.03, p=0.350) (Table 6).
Discussion
In this study, we have demonstrated that a longer mastoid process was correlated with the success of tympanoplasty. These results support the findings of Turgut (15), who suggested that the length of the mastoid tip was correlated with mastoid mucosal status.
Many prognostic factors have previously been shown to attribute to successful surgical outcomes of the tympanoplasty, including graft material, draining ear, mucosal inflammation, perforation size, and sclerotic mastoid.(2, 18, 19) E-tube function, mastoid pneumatization, and mastoid cavity size are also suggested as prognostic factors.(20) Hasebe et al. studied the association between mastoid aeration and cholesteatoma progression,(21) and suggested that cholesteatoma with a well-aerated mastoid cavity is less progressive and more manageable, even with conservative treatment. The middle ear risk index (MERI) was recently reported as a helpful tool for predicting the success rate of tympanoplasty. MERI consists of risk factors such as otorrhea, perforation, cholesteatoma, ossicle status, middle ear granulation, previous surgery, and current smoking status.(22, 23) Therefore, mastoid pneumatization, inflammation, and ossicle status seem to be necessary for the successful tympanoplasty outcomes.
In the current study, we used MPL as an indicator of mastoid pneumatization.(15) A longer mastoid process was associated with the successful surgical outcome of tympanoplasty without mastoidectomy for patients with COM. If mastoidectomy is not required, inflammation of the mastoid cavity can be minimal. However, when necessary, mastoidectomy can induce severe inflammation or destruction of the mastoid cavity and similar results are yielded respite differences in MPL.
Therefore, for well-preserved mastoid mucosa, improved surgical outcomes will be associated with pneumatization of the mastoid cavity, suggesting that MPL can be used as a preoperative indicator of successful surgery.
E-tube dysfunction has been associated with various middle ear diseases. Shraddha et al. reported that E-tube dysfunction affected tympanic retraction and mastoid pneumatization. Additionally, Kim et al. reported that the general E-tube test was significantly associated with surgical outcomes.(20) However, Hasebe et al. did not observe a significant association between E-tube function and cholesteatoma progression.(21) In this study, E-tube density measured in CT (ETD) did not correlate with reperforation. Furthermore, ETD was not associated with the MPL (data not shown). Aeration may determine MPL during mastoid development, and if mastoid and middle ear inflammation occur in adult life, as shown in this study (mean age =52.75), the correlation between ETD and MPL is doubtful. Moreover, because the imaging study was performed preoperatively, middle ear inflammation may have interfered with the exact measurement of the E-tube aeration. A postoperative CT study would be required to possibly elucidate the role of ETD.
The role of the mastoidectomy in achieving successful outcomes is controversial.(2, 18) From an extensive series review, Eliades et al. found that there was no additional benefit from performing mastoidectomy along with tympanoplasty to treat uncomplicated TM perforations.(2) Similarly, Callioglu et al. reported that performing mastoidectomy was not associated with hearing gain when treating COM of a low middle ear risk index.(24) On the contrary, McGrew et al. reported that patients who had tympanoplasty with mastoidectomy to treat simple TM perforation required a lower rate of follow-up procedure with a better disease eradication rate than those who had tympanoplasty alone.(14) In the present study, performing mastoidectomy along with tympanoplasty resulted in a higher success rate (94.6%) than performing tympanoplasty alone (78%) (Table 3). These results may be attributed to inflammation in the mastoid cavity that was not evaluated preoperatively. In the current study, mastoidectomy was performed in patients with prolonged disease duration, radiological evidence of mastoid involvement, and complications such as ossicular chain destruction, tegmen erosion, or persistent otorrhea. The success rate of the tympanoplasty alone was worse than that of the tympanomastoidectomy, because mastoid inflammation was not sufficiently eradicated.
In patients with tympanoplasty only, hearing may be associated with aeration of the middle ear. In this study, the postoperative ABG improvement was not correlated with MPL, and postoperative gap closure was also unrelated. Patients who received tympanomastoidectomy did not show a correlation between MPL and postoperative hearing outcomes. Besides middle ear aeration, ossicle mobility and the middle ear mucosa status are factors for improved hearing.(25) With multiple contributing factors, it’s possible that there is not no correlation between MPL and hearing outcomes.
In conclusion, a longer MPL was associated with a favorable surgical outcome when performing tympanoplasty without mastoidectomy. Performing ICWM in addition to tympanoplasty was associated with an improved success rate. Well-controlled and randomized trials on large cohorts can help to confirm these associations.
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