|Year : 2018 | Volume
| Issue : 1 | Page : 9-12
Effect of drill noise on contralateral hearing after mastoidectomy in cases of unilateral Chronic Otitis Media
Varun Jerath, Dilip Raghavan
Department of ENT, INHS Asvini, Mumbai, Maharashtra, India
|Date of Web Publication||9-Jul-2018|
Surg Capt Dilip Raghavan
Department of ENT, INHS Asvini, Mumbai - 400 005, Maharashtra
Source of Support: None, Conflict of Interest: None
Introduction: The mainstay of treatment of Chronic Otitis Media (COM) is Tympanoplasty with or without Mastoidectomy. This study was conducted in patients undergoing Tympanoplasty with Mastoidectomy to assess Sensorineural Hearing Loss (if any) due to drill noise on the contralateral ear. Materials and Methods: A total of 25 patients with unilateral COM scheduled to undergo Mastoidectomy and Tympanoplasty who fulfilled inclusion criteria were recruited in the study, and a prospective, observational pilot study was carried out. Pure Tone Audiometry (PTA) and Transient Evoked Otoacoustic Emissions (TEOAE) were recorded preoperatively and postoperatively to assess hearing loss if any on the contralateral side. Results: There was no change in bone-conduction thresholds in the contralateral ear by PTA postoperatively. However, there was a significant worsening in the values of signal-to-noise ratio of TEOAE at all the frequencies in the postoperative period. The mean TEOAE recordings were, however, above 3 dB SPL. Conclusion: There are statistically significant effects of drill noise on the inner ear function on the contralateral ear as detected by TEOAE; however, the effects are not detectable on PTA. Larger studies with a longer follow-up period will be required to determine if the early postoperative effects on TEOAE are reversible or persist.
Keywords: Chronic Otitis Media, effects of drilling, Mastoidectomy, Noise Induced Hearing Loss, Pure Tone Audiometry, Transient Evoked Otoacoustic Emissions
|How to cite this article:|
Jerath V, Raghavan D. Effect of drill noise on contralateral hearing after mastoidectomy in cases of unilateral Chronic Otitis Media. J Mar Med Soc 2018;20:9-12
| Introduction|| |
The diagnosis of Chronic Otitis Media (COM) implies a permanent abnormality of the Pars tensa or flaccida, with worldwide prevalence of 65–330 million people. It may be unilateral or bilateral, but most of the cases are unilateral.
Mastoidectomy is the mainstay of the treatment which may be cortical/intact canal wall/canal wall down Mastoidectomy. It has been postulated that Mastoidectomy can cause Sensorineural Hearing Loss (SNHL) due to the noise produced during drilling of the Temporal bone.
Exposure to high levels of noise is known to be harmful to the ear. Noise exposure to sound generated by a drill may result in a transient hearing deficit or permanent hearing impairment. It is thought that middle ear surgeries are themselves associated with SNHL and probable causes of postoperative hearing loss in a patient undergoing middle ear surgery are, noise due to drills, continuous suction irrigation, vibrations, inner ear injury, manipulation of ossicles, and a few unknown reasons.,,
This study aimed to find whether noise produced during drilling causes any hearing loss in the contralateral ear and to assess the severity of hearing loss.
| Materials and Methods|| |
A hospital-based prospective, observational pilot study was conducted in a tertiary care setting. A total of 25 patients were recruited in the study. Adult patients with unilateral COM scheduled to undergo Mastoidectomy and Tympanoplasty with normal hearing in the contralateral ear as determined preoperatively by Pure Tone Audiometry (PTA) and Transient Evoked Otoacoustic Emissions (TEOAE) and consenting were included in the study. Patients with bilateral COM with preexisting hearing loss in the contralateral ear or a history of head injury/SNHL/exposure to ototoxic drugs/noise exposure were excluded from the study.
The study protocol was reviewed and approved by the Ethics Review Committee of the hospital, where study was proposed to be carried out. An informed consent was obtained from the individuals.
A single surgeon (DR) performed all the surgeries. All patients undergoing Mastoidectomy were subjected to PTA and TEOAE preoperatively and on 1st and 7th postoperative day on the contralateral (nonoperated) ear.
Data were analyzed using Paired t-test.
| Results|| |
A total of 25 individuals participated in this study, of which 16 were male and 9 were female. The age of these individuals ranged from 18 to 51 years with the mean age of 35.12 years.
The majority of patients underwent cortical Mastoidectomy and Tympanoplasty for central perforations of the Pars tensa (16, 64%). The average drilling time in this series was 30 min.
The bone-conduction hearing thresholds on PTA of the normal/contralateral ear were the first parameter to be measured. There was no statistically significant worsening in PTA thresholds measured before and after surgery. The results are presented in [Table 1], [Table 2], [Table 3] and [Figure 1].
|Table 1: Comparison of study participants on the basis of Pure Tone Audiometry (dB HL), preoperative and 1st postoperative day (n=25) (paired t-test)|
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|Table 2: Comparison of the study participants on the basis of Pure Tone Audiometry (dB HL), preoperative and 7th postoperative day (n=25) (paired t-test)|
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|Table 3: Comparison of the study participants on the basis of Pure Tone Audiometry (dB HL) between 1st and 7th postoperative day (n=25) (paired t-test)|
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|Figure 1: Contralateral bone-conduction hearing thresholds (dB HL) by Pure Tone Audiometry|
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In this study, there was a statistically significant reduction in signal-to-noise ratio (SNR) of TEOAEs after Mastoidectomy was performed on the contralateral side. However, the SNR remained above the minimum recommended value of 3 dB SPL. This drop which was detected on the 1st postoperative day was seen in all frequencies tested from 0.5 to 4 kHz and persisted on the 7th postoperative day [Table 4], [Table 5], and [Figure 2]. There was no statistical difference in SNR values of TEOAE between the 1st and 7th postoperative day [Table 6].
|Table 4: Comparison of the study participants on the basis of Transient Evoked Otoacoustic Emissions signal-to-noise ratio between preoperative and 1st postoperative day (n=25) (paired t-test)|
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|Table 5: Comparison of the study participants on the basis of Transient Evoked Otoacoustic Emissions signal-to-noise ratio between preoperative and 7th postoperative day (n=25) (paired t-test)|
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|Figure 2: Assessment of signal-to-noise ratio based on Transient Evoked Otoacoustic Emissions|
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|Table 6: Comparison of the study participants on the basis of Transient Evoked Otoacoustic Emissions signal-to-noise ratio between 1st and 7th postoperative day (n=25) (paired t-test)|
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To summarize, there was no change in bone-conduction thresholds in the contralateral ear using PTA postoperatively. However, there was significant worsening in the values of SNR of TEOAE at all the frequencies in the postoperative period. The mean TEOAE recordings were, however, above 3 dB SPL.
| Discussion|| |
Ear surgery is associated with a risk of SNHL. The probable causes of postoperative hearing loss in a patient undergoing middle ear surgery are thought to be due to noise from drilling, continuous suction irrigation, vibrations, inner ear injury, manipulation of ossicles, and a few unknown reasons.,,,,,,
Drilling during Mastoid surgery forms the major part of the noise exposure during surgery and noise produced during drilling is transferred to both Cochleae by bone conduction. The sound intensity produced by drilling is estimated to be >100 dB. Since interaural attenuation by bone conduction is minimal (0–5 dB) and drill induced noise can cause hearing loss to the contralateral ear.
The average drilling time in our series was 30 min. Parkin et al. found that sound levels above 115 dB can cause SNHL if sustained for more than 15 min.
Kylén et al. pointed out that large cutting burrs produced more noise than fine small cutting burrs and the noise level was reduced when equivalent-sized diamond burrs were used.,
Various studies have been conducted in the past to assess whether there is drill induced hearing loss and whether the loss is temporary or permanent.,,,,,,,,,,
The present study compared preoperative and postoperative PTA and TEOAE for patients of COM who underwent Mastoidectomy. Cortical Mastoidectomy was the most commonly performed surgery.
Among the parameters measured, the preoperative BC was compared to the postoperative BC of the 1st and 7th postoperative day. No statistically significant difference was found between preoperative and postoperative BC values on PTA.
The second parameter measured was TEOAE of preoperative and postoperative period. TEOAEs are stable and unaffected by the effect of anesthesia, providing frequency-specific information about the functional integrity of the outer hair cells (OHCs).
Although, there was a statistically significant reduction in contralateral TEOAE SNR between the baseline and postoperative recordings, however, the mean SNR value recorded was still above 3 dB which is considered normal as per the current recommendations.,
This statistically significant reduction in the SNR values of TEOAE suggests subclinical inner ear damage which is not apparent on PTA. This suggests that effects of noise due to drilling can cause permanent damage to the inner ear.
In this study, the presence of noise-induced emission loss (significant difference in preoperative and postoperative TEOAE levels) in the absence of Noise Induced Hearing Loss as measured by PTA confirms that early noise-induced loss of OHC function as measured by TEOAE is more sensitive than pure-tone hearing thresholds.
Attias et al., have reported that noise-exposed, normal-hearing patients had reduced overall TEOAE with a narrow frequency range as compared to normal-hearing, patients not exposed to noise. Konopka et al. found an approximately 2-dB decrease in TEOAEs, but the only significant changes in audiometric thresholds were at 10 and 12 kHz. Sliwinska-Kowalska and Kotylo found that although there was no change in PTA of noise-exposed patients during 2 years of observation, a constant, gradual decrease in TEOAEs was observed.
The study results agree with similar studies carried out and show that there is some noise-induced emission loss which is recordable on TEOAE.
| Conclusion|| |
It is, therefore, probable that drill noise during Mastoidectomy does cause some OHC damage, though not significant enough to cause hearing loss as detected by PTA. This may be kept in mind while planning surgery, especially in patients with a poor cochlear reserve and in patients requiring repeat/multiple procedures, involving drilling of the temporal bone.
However, the larger studies with a longer period of follow-up may be required to conclusively confirm a cause-effect relationship.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]