<div>Can mastoid process length predict the surgical outcome of tympanoplasty
with or without canal wall up mastoidectomy in adults with chronic
otitis media?</div><div>Abstract</div><div>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.</div><div>Settings: Tertiary referral hospital</div><div>Participants: We included 127 patients who underwent tympanoplasty with
or without intact canal wall mastoidectomy.</div><div>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
&gt; 10 dB and Gap closure as a binary outcome with cutoff
&gt;= 0 dB.</div><div>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).</div><div>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.</div><div>Keywords: outcome, tympanoplasty, chronic otitis media, mastoid process,
mastoidectomy</div><div>Key points</div><div>- Mastoid process length (MPL) is related to the surgical success after
tympanoplasty in patients with chronic otitis media.</div><div>- Success was significantly higher in patients who received
tympanomastoidectomy than in those who received tympanoplasty only.</div><div>- The possibility of reperforation decreased by 9 ~ 12%
for a unit (mm) increase in MPL.</div><div>- Reperforation decreases by 32% for a 1 mm increase of MPL in patients
who received tympanoplasty only.</div><div>- Postoperative hearing outcomes were not affected by MPL.</div><div>Introduction</div><div>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.</div><div>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.</div><div>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.</div><div>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.</div><div>Materials and Methods</div><div>Study design</div><div>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 &lt;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.</div><div>Evaluation of the parameters</div><div>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.</div><div>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.</div><div>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).</div><div>Outcome measurement</div><div>The primary outcome of this study was whether MPL correlated with the
success of tympanoplasty at 1 year after surgery.</div><div>The secondary outcome was the correlation between MPL and postoperative
hearing outcomes. Our analysis used ABG as a binary outcome with a
cutoff of &gt;10 dB and gap closure as a binary outcome with a
cutoff of &gt;= 0 dB.</div><div>Statistical Analysis</div><div>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’s<i>t</i> -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.</div><div>A P-value of &lt;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.</div><div>Results</div><div>3.1. Patients characteristics</div><div>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).</div><div>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.</div><div>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).</div><div>3.2. Association of MPL with the possibility of reperforation</div><div>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.</div><div>3.3. Association of MPL with postoperative hearing results</div><div>Hearing outcome was determined by the air-bone gap and gap closure
measured at 1 year after surgery. ABG was categorized as = &lt;10
dB and &gt;10 dB. Table 5 shows the univariate logistic
regression analysis for the ABG &gt;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).</div><div>E-tube density did not show a significant correlation with postoperative
ABG for all patients and in the subgroup analysis.</div><div>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).</div><div>Discussion</div><div>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.</div><div>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.</div><div>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.</div><div>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.</div><div>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.</div><div>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.</div><div>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.</div><div>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.</div><div>References</div><div>1. Andersen S, Aabenhus K, Glad H, Sørensen M. Graft Take-Rates After
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