Abstract
Chronic suppurative otitis media is managed by tympanomastoid surgery often requires mastoid drilling. Sometimes patients develop sensorineural hearing loss after middle ear surgery. Objective of the study was to compare pre and post operative bone conduction thresholds after middle ear surgeries. The study was conducted on 90 patients who had undergone middle ear surgeries, 30 patients of tympanoplasty (group I), modified intact canal wall mastoidectomy and tympanoplasty type-I (group II) and modified radical mastoidectomy (group III) each ware included. Demographic and clinical data were reviewed. Duration of surgery, ossicular and middle ear status and drilling time noted. Pre operative and post operative (after 3–4 months) bone conduction thresholds were compared statistically. A value of p < 0.05 was considered statistical significant. The average pre-operative hearing loss of study group was 43.78 ± 14.22 dB. Though postoperatively mean air conduction threshold improved to 36.07 ± 13.05 dB, six patients presented with deterioration of hearing. Mastoidectomy has been performed in all six. Post-operative worsening of bone conduction was seen in three patients (13.75–21.5 dB), one patient of group II and two patients of group III developed postoperative worsening of bone conduction thresholds. Significant hearing losses may occur after tympanomastoid surgery in few patients. While we are evaluating the results besides reporting average results such individual patient should be identified.
Keywords: Post-operative sensorineural hearing loss, SNHL, Masotidectomy, Mastoid drilling
Introduction
Surgery is definitive treatment for chronic suppurative otitis media (CSOM). Surgical technique and procedure varies according to the individual case findings and pathology and may require either an intact canal wall (ICW) or a canal wall down (CWD) mastoidectomy to eradicate disease from the mastoid air cell system [1, 2]. Although hearing impairment is one of the most common sequelae of CSOM, patients may develop additional hearing loss after tympanomastoid surgery [2]. The surgical treatment of chronic middle ear disease is associated with a risk of damage to the inner ear. The incidence of permanent sensorineural hearing loss after tympanomastoid surgery is 1.2–4.5% [3]. This is probably due to damage to delicate inner-ear structures as a result of damage to oval or round windows during removal of cholesteatoma or granulations from these areas, acoustic trauma from drill generated noise or from the suction, opening of lateral semicircular canal while removing cholesteatoma matrix resulting in labyrinthine fistula, and inadvertently touching the ossicles with a rotating burr [4, 5].
Bone drilling and suction are essential in ear surgery, but they expose cochlea to significant noise and vibrations of high speed drill. During drilling the exposed cochlea may be subjected to noise levels of 90–100 dB, while the contralateral cochlea to 80–85 dB. Vibration of temporal bone may have implications leading to cochlear damage, and both drill and suction generated noise and vibration may have additive effect in damaging the cochlea [4, 5]. The sound emission generated by newer and better drilling systems using different surgical burs routinely used in temporal bone surgery is lowered. Still, within a small radius around those burs high sound pressure levels may be induced into surrounding structures such as ossicles, labyrinth, and cochlea [6].
In the presented study bone conduction threshold was evaluated after middle ear surgery and compared with pre operative bone conduction threshold. The change in bone conduction threshold was compared in three different group of patients who underwent tympanoplasty, intact canal wall procedure and canal wall down procedure.
Material and Method
The study was conducted in a tertiary health care centre of India from January 2016 to December 2016 in the cases of chronic suppurative otitis media who had undergone middle ear surgeries in the institute. Patients suffering from preoperative sensorineural hearing loss, occupational noise exposure, history of ototoxic drug intake, previous middle ear surgery and post-operative discharging ear were excluded from the study. The study was approved from the medical research review and ethical board of the institute. Post operative cases of CSOM, operated in the department under regular follow-up in otology clinics were identified as target population. Patients with uptake of graft, no post-operative discharge and willing for participation in the study were enrolled. The study patients were divided into three groups of 30 cases each on the basis of their earlier surgical management. Group I included patients, who had undergone tympanoplasty, group II patients had undergone modified intact canal wall mastoidectomy and tympanoplasty (MICT) type I and group III included modified radical mastoidectomy (MRM) patients.
Patient case record sheets and discharge summaries were reviewed for their presenting complaints, middle ear findings, routine investigations, pre-operative pure tone audiometry, radiological findings, intra-operative findings, drilling time and surgical procedure performed. Different drilling systems and different size of cutting and diamond burs have been used for mastoidectomy. All cases were subjected to post operative pure tone audiometry (PTA) three to four months after surgery. The pre and post-operative hearing evaluations were performed in a sound proof audiometry room by same audiologist. Air conduction and bone conduction threshold of all these patients have been recorded for 0.5, 1, 2 and 4 kHz. Hearing results were reported as the mean and standard deviation of the air conduction thresholds, bone conduction thresholds, and air–bone gap. Pre and post-operative thresholds were compared. Statistical analysis of these results was performed by OpenEpi software [7]. A value of p < 0.05 was considered statistical significant.
Observations
The study was conducted on 90 patients of CSOM operated in the Institute, out of them 37 (41%) were males and 53 (59%) females. The age of the patients included in the study ranged from seven to 60 years with mean age of 24.51 ± 11.18 years. The commonest age group was 11–20 years having 39 (43%) patients. The commonest complaint of patients was ear discharge presented in all patients (n = 90). Other complains were hearing impairment by 84% (n = 76), associated earache in 6% (n = 5) of patients and tinnitus in 4.44% (n = 4) (Table 1).
Table 1.
Demographic characteristic and clinical presentations of study population
| Group I tympanoplasty (n = 30) |
Group II MICT (n = 30) |
Group III MRM (n = 30) |
Total (n = 90) |
|
|---|---|---|---|---|
| Age (years) | ||||
| Mean ± SD | 25.1 ± 10.28 | 25.56 ± 9.96 | 22.86 ± 13.19 | 24.51 ± 11.18 |
| Range | 12–57 | 12–54 | 7–60 | 7–60 |
| Sex | ||||
| Male | 8 (26.66%) | 12 (40%) | 17 (56.66%) | 37 (41%) |
| Female | 22 (73.33%) | 18 (60%) | 13 (43.33%) | 53 (59%) |
| Chief presenting complains | ||||
| Ear discharge | 30 (100%) | 30 (100%) | 30 (100%) | 90 (100%) |
| Decrease in hearing | 19 (63.33%) | 27 (90%) | 30 (100%) | 76 (84%) |
| Side of disease | ||||
| Right | 12 (40%) | 10 (33.33%) | 14 (46.66%) | 36 (40%) |
| Left | 13 (43.33%) | 13 (43.33%) | 13 (43.33%) | 39 (43.33%) |
| Bilateral | 5 (16.66%) | 7 (23.33%) | 3 (10%) | 15 (16.66%) |
| Duration of ear discharge in operated ear in years | ||||
| Mean ± SD | 9.1 ± 9.25 | 7.47 ± 5.63 | 15 ± 7.08 | 10.52 ± 8.07 |
| Duration of hearing loss in operated ear in years | ||||
| Mean ± SD | 3.65 ± 5.57 | 3.1 ± 3.40 | 7.27 ± 3.56 | 4.672 ± 4.63 |
Pre-operative audiometry showed that 38.88% (n = 35) patients had moderate hearing loss followed by moderately severe hearing loss in 22.22% (n = 20). The average pre-operative hearing loss of study group was 43.78 ± 14.22 dB. Mastoid drilling was done in group II and group III patients. Drilling duration was less than 30 min in 40 (44.44%) patients and more than 30 min in 20 (22.22%) patients with mean duration of drilling of 28.45 ± 6.69 min. Mean duration of surgery was 102 ± 41 min. After three months of surgery out of 90 patients of study population six (6.67%) experienced deterioration of hearing clinically. In group I (tympanoplasty) 19 patients had pre-operative hearing loss, out of them 11 reported improvement and eight not much change in hearing. In rest 11 there was no complain of pre/post-operative hearing loss. In group II (MICT-I) out of 27 patients complaining pre-operative hearing loss, 16 patients reported improvement, eight not much change and three decrease in hearing. Three patients had no pre and post-operative complains of hearing loss. While in group III (MRM) all 30 patients had preoperative hearing loss, seven reported improvement, 20 not much change and three reported deterioration in hearing.
Postoperatively mean air conduction threshold was 36.07 ± 13.05 dB. Out of 90 patients, 26.66% (n = 24) had bone conduction level between 11 and 15 dB followed by more than 20 dB in 25.55% (n = 23). Mean post-operative bone conduction threshold was 17.09 ± 8.60 dB (Table 2). These results showed that in all three groups post operative air conduction threshold and AB gap improved significantly. The changes in post-operative bone conduction threshold were statistically non-significant (Table 2).
Table 2.
Comparison of pre and post operative hearing in different study groups
| (n = 30 in each group) | Preoperative hearing threshold | Postoperative hearing threshold | p value |
|---|---|---|---|
| Mean (dB) ± SD | Mean (dB) ± SD | ||
| Air conduction | |||
| Group I | 35.5 ± 14.15 | 26.21 ± 8.67 | < 0.01 |
| Group II | 40.95 ± 16.28 | 32.91 ± 17.45 | < 0.01 |
| Group III | 54.88 ± 8.67 | 49.1 ± 8.53 | < 0.05 |
| All patients (n = 90) | 43.78 ± 14.22 | 36.07 ± 13.05 | < 0.01 |
| Bone conduction | |||
| Group I | 9.53 ± 5.55 | 10.29 ± 5.76 | 0.60 |
| Group II | 16.28 ± 6.28 | 17.45 ± 6.87 | 0.53 |
| Group III | 20.21 ± 6.92 | 23.16 ± 7.15 | 0.1 |
| All patients (n = 90) | 15.34 ± 7.62 | 17.09 ± 8.60 | 0.15 |
| Air-bone gap | |||
| Group I | 25.98 ± 10.72 | 15.91 ± 6.81 | < 0.01 |
| Group II | 24.68 ± 9.84 | 15.46 ± 7.78 | < 0.01 |
| Group III | 34.66 ± 7.23 | 25.93 ± 6.27 | < 0.01 |
| All patients (n = 90) | 28.43 ± 10.29 | 18.97 ± 8.30 | < 0.01 |
To further understand these changes pre and post-operative hearing threshold of each patient plotted on a scattered graph (Fig. 1). The x-axis is post-operative hearing threshold in dB and y-axis represent pre-operative hearing threshold. Each patient in three different groups is placed appropriately. Diagonal black line is drawn at 45°. Patient left to the line having better post-operative hearing while those on right side have worsened postoperative hearing. Green and red color parallel lines are drawn on left and right respectively at 10 dB marks on either side of midline. Patient left to green line are having more than 10 dB gain postoperatively while those who are right to red line are having more than 10 dB worsening. Figure 1a shows that majority of patient have better postoperative hearing in all three groups. Few patients were having similar postoperative hearing, however six patients developed post-operative worsening of hearing. Figure 1b for bone conduction showed that most patients were plotted near diagonal line between green and red lines. Few patients were near red line indicating postoperative worsening of about 10 dB. One patient of group II and two patients of group III are worth mentioning having postoperative worsening of 13.75–21.5 dB. The group II patient was having retraction pocket in attic going towards aditus adhering to incus with intact ossicular chain. Two patients of group III were having extensive cholesteatoma and granulations. There was cholesteatoma with fistula of lateral semi circular canal in one patient.
Fig. 1.
Scatter diagram showing pre and post operative hearing threshold of each patient in different groups of study population. MICT modified intact canal wall mastoidectomy with tympanoplasty; MRM modified radical mastoidectomy
Pre and post-operative mean bone conduction thresholds for 500, 1000, 2000 and 4000 Hz were compared for all three groups. There were minimal changes for 500 and 1000 Hz, for higher frequencies 2000 and 4000 Hz statistically non significant worsening of bone conduction threshold were observed. The worsening was more in cases of MRM (Table 3). Pre and post operative mean bone conduction thresholds were also compared for different factors which may affect post operative bone conduction threshold i.e. duration of drilling, duration of disease symptoms, pneumatisation of mastoid and disease pathology. Statistically non-significant post operative worsening of bone conduction threshold was found in patients in whom drilling was done for more than 30 min, duration of ear discharge was more than 10 years, mastoid was sclerosed and with presence of granulations and cholesteatoma.
Table 3.
Comparison of pre and post operative mean bone conduction thresholds (dB) for different frequencies
| Frequency (Hz) | Bone conduction threshold (preoperative) | Bone conduction threshold (postoperative) | p value | ||
|---|---|---|---|---|---|
| Mean (dB) | SD | Mean (dB) | SD | ||
| Group I: tympanoplasty (n = 30) | |||||
| 500 | 3.83 | 3.86 | 3.83 | 3.39 | – |
| 1000 | 7 | 5.01 | 7.33 | 4.49 | – |
| 2000 | 10.17 | 6.36 | 11.67 | 6.68 | 0.38 |
| 4000 | 17.17 | 10.48 | 18.33 | 11.47 | 0.84 |
| Group II: MICT (n = 30) | |||||
| 500 | 8 | 3.85 | 8 | 3.85 | – |
| 1000 | 12 | 5.34 | 12 | 5.81 | – |
| 2000 | 16.17 | 6.39 | 17.33 | 7.15 | 0.51 |
| 4000 | 29 | 12.95 | 31.67 | 12.89 | 0.42 |
| Group III: MRM (n = 30) | |||||
| 500 | 11 | 4.8 | 11.67 | 4.61 | 0.58 |
| 1000 | 14.33 | 5.2 | 16.5 | 5.75 | 0.13 |
| 2000 | 19.83 | 8.14 | 24 | 8.24 | 0.054 |
| 4000 | 35.67 | 13.37 | 40.5 | 14.22 | 0.18 |
Discussion
Middle ear and mastoid surgery for CSOM is being done to make the ear safe and dry and to restore the hearing. Presence of edematous mucosa, granulations, fibrotic adhesions, tympanosclerotic patches, medialised handle of malleus, retraction pouch and cholesteatoma in middle ear and mastoid cavity require drilling and fine manipulations in mastoid and near the ossicles.
Sensorineural hearing loss though rare to happen, is one of the most important complications of the middle ear surgery. Tos as early as in 1984 reported the sensorineural hearing loss in a total of 1.2% of cases after chronic ear surgery [8]. He reported that the occurrence was highest in congenital malformations, granulating otitis and cholesteatoma, and mastoidectomy (especially canal-down). The most common causes reported were removal of cholesteatoma from the semicircular canal and removal of the fistula membrane [8]. Almost same figures were reported for ear surgery by Prinsley [5] in his audit of ‘dead ear’ in 2013. But the overall ratio of post-operative dead ear was high (2.7%) in adults patient who underwent mastoid surgery for cholesteatoma [5]. It is difficult to pinpoint a single cause as various factors might be responsible for this untoward complication. The most frequent reason seems to be cochlear damage induced by excessive movements of the chain and acoustic trauma induced by drill and suction [5, 9]. Kazikdas et al. [9] concluded that over-under tympanoplasty, which requires significant manipulation of the ossicles, can cause temporary SNHL after surgery (23%), and prolonged exposure to the noise generated by mastoid drilling can result in permanent SNHL (16%).
We noted that although the post-operative mean ± SD for air conduction and AB gap was significantly lower than pre-operative thresholds, there was worsening of air conduction in six patients. Similarly we noticed that though the change in mean bone conduction was not significant, still three patients were having significant worsening of bone conduction (Table 2). Hereby we want to stress that the reporting of data as average may divert the focus away from those few patients who has not been benefitted even worsened. So we suggest plotting the data of pre-operative and post-operative hearing thresholds as a scatter diagram. This graphical representation helps in identification of those individual patients, and better interpretation of results (Fig. 1).
Mastoidectomy is being done for more than 180 years using the trepan (in the eighteenth century); the chisel and gouge (in the second half of the nineteenth and first half of the twentieth century’s) and afterwards by electrical drills. Over the time the drilling and suction-irrigation system improved a lot [10]. Holmquist et al. [11] reported that the intensity of mastoid drilling can reach up to 125 dB, with a mean that is constantly above 100 dB. Prasad et al. [12] recorded sound levels during the use of powered instruments in ENT surgery in 2003 and found that the sound levels emitted by cutting burs varied from 68.8 to 72.4 dB (small to larger burs) and 60.8 dB for diamond burs. Dalchow et al. investigated noise levels generated by otologic drills and reported in 2015 that the highest sound rate generated by the diamond burr did not exceed 63 dB, whereas the cutting burr emitted 76 dB. The sound generated by newer instruments is well within the safety guidelines [6].
High frequency hearing loss can be caused by inadvertent drilling on the ossicular chain. Vibratory force produced by drilling is analogous with noise levels known to produce acoustic trauma. It is generally considered cutting and large diameter burr produces more vibratory force. The cutting burr produces greater high frequency than lower-frequency vibratory energy [13]. Sutinen [14] shown in the guinea pig model that the temporal bone vibration at higher frequencies produced a more severe hearing loss than did the vibration at lower frequencies.
Banakis Hartl et al. [3] studied drill-induced cochlear Injury during otologic surgery in cadavers. They placed fiber-optic sensors in scala tympani and vestibuli to measure intracochlear pressures and used single-axis laser doppler vibrometry to measure stapes velocities. The drill was kept in such way that the edge of the burr maintained light contact with the body and short process of the incus for 5–10 s, during which time intracochlear pressures and stapes velocity, were recorded. They concluded that incidental drilling on the ossicular chain during middle ear surgery can generate estimated peak equivalent ear canal pressure ranged from 134 to 165 dB SPL and cause sensorineural hearing loss [3].
Goyal et al. [15] concluded that mastoid drilling poses a threat to hearing in the contralateral ear due to noise and vibration conducted transcranially. Baradaranfar et al. [4] studied the effect drill-generated noise in the contralateral healthy ear following mastoid surgery in 28 patients. They performed standard PTA and distortion-product otoacoustic emission (DPOAE) were measured in all contralateral ears before and 6, 24, 48, 72, and 96 h after the surgery. They concluded that high-frequency hearing loss usually occurs following mastoid surgeries is mainly temporary and reversible after 72 h. Similarly Abtahi et al. [16] also concluded that drill-induced noise during mastoidectomy can cause reversible changes in PTA, DPOAEs and transient evoked otoacoustic emissions (TEOAEs) in the non-operated ear.
Manipulation of the ossicular chain while removing squamous epithelium from the handle and neck of the malleus can cause sensorineural hearing loss during surgery. Gentle dissection performed in parallel with the malleus handle can minimize this complication [17]. Bewick et al. [18] in a series of myringoplasty operations reported that out of 187 patients, 44 (23.53%) experienced a reduction in hearing thresholds and in seven cases (3.74%), the hearing loss was greater than 10 dB. Thus avoidance of postoperative sensorineural hearing loss depends on multiple factors and evaluation of magnitude of hearing loss in relation to these factors is important to determine the success of surgery.
Prinsley in his ‘audit of dead ear’ reported that the dead ear was inevitable in several cases due to disease progression and disease duration and even with meticulous surgical technique, rarely, iatrogenic dead ear can occurs. He advocated careful consenting, candid explanation and realistic rehabilitation if dead ear occurs, are crucial in management of CSOM [5]. There have been certain limitations in our study, the study was retrospective in nature and the participants were selected from the otologic clinic follow-ups so the data may represent more dissatisfied patients with worse hearing or less benefit in hearing, we have omitted patients with failed grafting and active discharge, different drilling systems were used, and different and multiple surgeons operated the cases. Though the study group may not be true representation of general patients, however the possibilities of post-operative sensorineural hearing loss should always be kept in mind and patient should be informed about it beforehand while explaining the surgical procedure and obtaining consent.
Conclusion
The patient developing post-operative sensorineural hearing loss should be identified and discussed in otology clinics and their surgical video recordings may be reviewed to ascertain the cause of development of post-operative sensorineural hearing loss. Patient with long duration of presentation and cholesteatoma may develop post-operative worsening of bone conduction.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interests.
Ethical Approval
All procedures performed in presented study involving human participants were in accordance with the ethical standards of the institutional research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Financial Support/Grant
No financial funding received. Patients were treated free of cost under ‘MNDY (Mukhyamantri Nishulk Dava Yojana) scheme’ and Bhamashah Yojana sponsored by Government of Rajasthan.
Informed Consent Statement
Informed consent was obtained from all individual participants included in the study.
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