Effect of Drill Induced Noise on Contralateral Normal Ear Following Cortical Mastoidectomy

Abstract

Introduction: Chronic suppurative otitis media (CSOM) is a long standing infection of the middle ear cleft. Mastoidectomy, with or without tympanoplasty, is the preferred treatment for CSOM. However, the drill used during ear surgery generates noise that may potentially cause hearing damage in both the operated and opposite inner ear, leading to temporary or permanent hearing loss. Materials and Methods: The study included patients diagnosed with CSOM who underwent surgeries in the Otorhinolaryngology department. Postoperatively, all patients were followed up on the 7th day and 1 month after the surgery. Pure Tone Audiometry (PTA) was performed to evaluate the hearing outcomes. Results: A total of 61 patients were included in the study. The mean preoperative PTA of contralateral ear bone conduction among the study participants was 6.48. At the 7th day post-operation, the mean post-operative PTA of contralateral ear bone conduction for the same participants was 7.77. This difference was statistically significant according to the Paired T-test (P = 0.001).However, when evaluating the mean preoperative PTA of contralateral ear bone conduction (6.48) and the mean post-operative PTA at 1st month (6.02), the difference was not statistically significant (P = 0.208).Additionally, there was no statistical difference in air conduction and air-bone gap before and after surgery. Conclusion: The study suggests that mastoid drilling is associated with a significant temporary hearing loss in the contralateral ear immediately after surgery, which eventually recovers within a month. However, the hearing loss is considered negligible and not statistically significant in the long term. It is worth considering additional audiological investigations, such as otoacoustic emissions, to detect this type of hearing loss more accurately.

Introduction

Chronic otitis media (COM) is a prevalent condition affecting a significant portion of the global population, ranging from 65 to 330 million people. A common manifestation of COM is a permanent perforation in pars tensa. The mainstay treatment for this condition is mastoidectomy, a surgical procedure involving bone drilling [1]. Research has indicated that surgical trauma and the noise produced during cortical mastoidectomy may contribute to sensorineural hearing loss (HL) during ear surgery [2]. Hearing loss induced by noise exposure can occur either due to loud noises repeatedly over an extended period or sudden loud “impulse” sounds, such as explosions [3].

Studies have demonstrated that noise from drills during tympano-mastoid surgery, exceeding 100 dB, may contribute to hearing loss [4]. However, the extent of hearing impairment depends on the intensity of the noise and the duration of exposure to the cochlea. Following tympano-mastoid surgery, a persistent sensorineural hearing loss appears to affect around 1.2–4.5% of patients in the operated ear5-7. However, the impact of drill noise on the unoperated ear, which is also subjected to the noise, has received less attention. Prolonged acoustic trauma to the opposite ear can lead to temporary hearing loss, though the reduction in hearing threshold is generally only 5–10 dB [5].

Both direct transmission through the skull and indirect transmission around the ear can result in drill-induced noise reaching the unoperated ear [2]. In light of these considerations, this study was undertaken to investigate whether drilling noise has any effect on hearing loss in the opposite ear following mastoidectomy. The specific objectives were to determine whether any hearing loss in the unoperated ear would be transient or permanent and to explore the relationship between hearing loss and drill-induced noise in patients who underwent mastoidectomy for COM.

The findings from this study could shed light on the potential risks associated with drill-induced noise during otological surgery and help improve safety measures to protect patients’ hearing during these procedures. Understanding the impact of surgical noise on the unoperated ear may also aid in optimizing surgical techniques and reducing potential hearing-related complications in patients with chronic otitis media.

Objectives

To describe the hearing acuity of the opposite normal ear after mastoid operation in patients with unilateral CSOM undergoing Tympanoplasty with cortical mastoidectomy.

Materials and Methods

The study included patients with unilateral chronic otitis media who underwent Tympanoplasty with cortical mastoidectomy. The study was conducted at the department of Otorhinolaryngology, RL Jalappa hospital and research centre attached to Sri Devaraj Urs Academy of Higher Education and Research Tamaka, Kolar between January 2021 and August 2022, spanning 1 year and 8 months.Patients between 18 and 60 years of age and patients with unilateral CSOM requiring Tympanoplasty with cortical mastoidectomy were included in our study.Patients with a history of using ototoxic drugs, patients undergoing ear surgeries other than cortical mastoidectomy, patients with bilateral sensorineural hearing loss, regardless of the cause were excluded from our study.

Thorough history taking and clinical examination of the patients were conducted, and the findings were recorded in a structured proforma.Pure Tone Audiometry (PTA) was performed on all patients to assess their hearing acuity preoperatively.Coronal and axial views of plain High-Resolution Computerized Tomography (CT) of the temporal bones were obtained as part of the standard preoperative haematological examinations.After obtaining anaesthetic approval for the mastoidectomy surgery, the patients underwent the surgical procedure. Postoperatively, on day 7 (the day of surgery considered as Day 0), PTA of the opposite ear was performed for all patients to assess the hearing acuity of the contralateral normal ear.Regular follow-ups were conducted once a month after the surgery, and PTA was repeated during each follow-up visit.The study received ethical approval from the Institutional Ethics Committee with No. SDUMC/KLR/IEC/646/202–2021. All ethical guidelines and principles were adhered to throughout the study.

SURGICAL PROCEDURE:The external auditory canal (ear canal) was instilled with 4% lignocaine The ear and surrounding areas were cleaned and disinfected using a 10% povidone iodine solution.A mixture of 10ml of 2% premix (xylocaine 2% and adrenaline 1:200,000) and 10ml of normal saline was injected into the postauricular area (behind the ear) and the external auditory meatus (ear canal).Betadine was used to wash the ear canal.An incision was made using Lempert’s endaural speculum, 5 mm lateral to the fibrous annulus (ringlike structure) at the 6 o’clock and 12 o’clock positions. These incisions were then joined with a horizontal incision.The skin in the posterior metal area was lifted laterally up to the bony cartilaginous junction. A William Wilde postaural incision was made about 0.5-1 cm away from the postauricular groove. Temporalis fascia, a tissue layer from the temple region, was harvested to be used as a graft.The margins of the perforation in the eardrum were freshened and the tympanomeatal flap was elevated. Ossicular status was assessed and round window reflex was confirmed.The malleus handle was skeletonised and the harvested temporalis fascia graft was placed using the underlay technique.Anterior tucking was performed.Repositioning of the tympanomeatal flap was done.postauricular wound was closed in layers and mastoid dressing was applied. Patients were prescribed antibiotics, analgesics and antihistamines for 7 days.Postaural sutures were removed 10 days after the surgery. The canal pack was removed on the 21st postoperative day. Pure Tone Audiometry (PTA) was done on the 7th day and again at the end of the 1st month post-surgery to assess hearing improvement.

Statistical Analysis

The collected data were entered in Ms excel and analysed using IBM.SPSS statistics software 23.0 Version. The data was described in descriptive statistics as frequency analysis, percentage analysis was used for discrete variables. Mean, Median and Standard deviation was used for continuous variables.To study the association of contralateral ear air, bone conduction and air-bone gap among the study participants between pre-operative PTA and Post-operative PTA at 7th day and end of first month, paired T test was used.In all the above statistical tools the probability value(p) 0.05 was considered as significant level.

Results

The mean age of the participants was 34.16 years, with a standard deviation of 8.092 years.The mean duration of ear pain symptoms was 2.3 days, with a standard deviation of 1.3 days.The majority of participants were males (59%).The most common type of ear pain reported by participants was throbbing (52.5%).Pricking type of ear pain was reported by 26.2% of participants.Dull aching ear pain was reported by 21.3% of participants.Approximately 49% of participants had mucopurulent ear discharge.Tinnitus was observed in about 10% of patients.Right ear was affected in the majority of patients (52%) compared to the left ear (48%).

The mean preoperative Pure Tone Audiometry (PTA) of contralateral ear air conduction was 11.89.The mean post-operative PTA of contralateral ear air conduction at 7th day was 12.16. The mean difference was not statistically significant according to the paired T-test (P = 0.4274).The mean post-operative PTA of contralateral ear air conduction at 1st month was 11.93. The mean difference was not statistically significant according to the paired T-test (P = 0.9083) as shown in Table 1. The mean preoperative PTA of contralateral ear bone conduction was 6.48.The mean post-operative PTA of contralateral ear bone conduction at 7th day was 7.77. The mean difference was statistically significant according to the paired T-test (P = 0.001).The mean post-operative PTA of contralateral ear bone conduction at 1st month was 6.02. The mean difference was not statistically significant according to the paired T-test (P = 0.208) as shown in Table 2. The mean preoperative PTA of contralateral ear air-bone gap was 3.91.The mean post-operative PTA of contralateral ear air-bone gap at 7th day was 4.30. The mean difference was not statistically significant according to the paired T-test (P = 0.121).The mean post-operative PTA of contralateral ear air-bone gap at 1st month was 3.64. The mean difference was not statistically significant according to the paired T-test (P = 0.321) as shown in Table 3.

Table 1.

Association of contralateral ear air conduction among the study participants between pre-operative PTA and post-operative PTA at 7th day and end of first month (n = 61)

S. No	Paired Samples Statistics	Mean	Std. Deviation	Mean difference	T - Value	P - Value	Statistical significance
1	Preoperative PTA of contralateral ear air conduction	11.89	2.131	− 0.270	− 6.791	0.4274	No Significant difference
	Post-operative PTA of contralateral ear air conduction at 7th day	12.16	1.572
2	Preoperative PTA of contralateral ear air conduction	11.89	2.131	− 0.04	− 2.459	0.9083	No Significant difference
	Post-operative PTA of contralateral ear air conduction at the end of 1st month	11.93	1.167

Table 2.

Association of contralateral ear bone conduction among the study participants between pre-operative PTA and post-operative PTA at 7th day and end of first month (n = 61)

S. No	Paired Samples Statistics	Mean	Std. Deviation	Mean difference	T - Value	P - Value	Statistical significance
1	Preoperative PTA of contralateral ear bone conduction	6.48	2.454	− 1.295	− 3.420	0.001	Significant difference
	Post-operative PTA of contralateral ear bone conduction at 7th day	7.77	1.216
2	Preoperative PTA of contralateral ear bone conduction	6.48	2.454	0.459	1.274	0.208	No significant difference
	Post-operative PTA of contralateral ear bone conduction at the end of 1st month	6.02	1.565

Table 3.

Association of contralateral ear air-bone gap among the study participants between pre-operative PTA and post-operative PTA at 7th day and end of first month (n = 61)

S. No	Paired Samples Statistics	Mean	Std. Deviation	Mean difference	T - Value	P - Value	Statistical significance
1	Preoperative PTA of contralateral ear air-bone gap	3.92	1.282	-0.377	− 1.573	0.121	No significant difference
	Post-operative PTA of contralateral ear air-bone gap at 7th day	4.30	1.564
2	Preoperative PTA of contralateral ear air-bone gap	3.92	1.282	0.2800	-3.528	0.321	No Significant difference
	Post-operative PTA of contralateral ear air-bone gap at the end of 1st month	3.64	1.782

Discussion

The major goal of this study was to ascertain how drill noise affected patients who were planned for tympanomastoid surgery on the contralateral ear in cases of unilateral CSOM. There is conflicting information in the literature on the impact of drilling during mastoid surgery on the unoperated ear.

Bone drilling is a crucial part of otological surgery, but it exposes both cochleae to a significant amount of vibration and noise. The intricate interaction between the transmission and damping properties of the skull, cranial contents, and surrounding soft tissue is represented by transcranial vibration. The noise produced by the drill during the mastoid surgery may be conveyed directly to both cochleae via bone vibration because there is little interaural attenuation of the skull. Sensorineural hearing loss can be brought on by drilling noise in the ear that is not affected. The otologic drill is a powerful vibration generator in addition to a source of noise. A powerful oscillation is sent into the cochlea during otologic drilling. Burr noise stimulation combined with movement of the cochlear parts can harm the cochlea more than noise alone [6, 7].

In our study, average age of research participants was 34.16 years, with a standard deviation of 8.092 years. About 52% of the study’s subjects were afflicted on their right side, while 48% were affected on their left.

In our study, according to mean air conduction, bone conduction, and air-bone gap measured in the contralateral ear when the patients were monitored preoperatively and up to postoperative day 7 and one month after surgery, there was no significant difference in the mean value of PTA.

According to some studies, sensorineural hearing loss can occur between 1.2% and 4.5% of the time in ears that have had drilling done. Along with these examinations, another study showed that, despite minor drilling-related alterations in the operated ear, there was no statistically significant change in the hearing level of the contralateral ear. It has been stated that additional sources of potential postoperative sensorineural hearing loss should be looked into because sensorineural hearing loss linked with drilling does not occur even in the operated ear after tympanomastoid surgery [8].

The pre- and postoperative bone conduction thresholds for frequencies 0.25 to 16 kHz were examined in a research by Hallmo and Mair involving 46 participants. They noticed that neither the operated ear nor the ear on the opposite side showed any statistically significant postoperative threshold shift at any particular frequency. While not present in the contralateral unoperated ear, the mean threshold increase of 1.4 dB for the ipsilateral extended high-frequency octave of 8–16 kHz was marginally significant (p = 0.02) [9].

Tos et al. performed the trans-labyrinthine operation on 50 consecutive patients to remove a unilateral acoustic neuroma. According to statistics, there is no decline in hearing in the opposite ear that can be linked to potential acoustic stress after trans-labyrinthine bone resection [10].

There could be a number of causes for the absence of hearing loss in the opposite ear. A tiny (1–4 mm) diamond burr was used for the majority of the surgery to do the cortical mastoidectomy. The Kylen et al. study, which looked at factors influencing drill-generated noise during ear surgery, demonstrated how the noise made by diamond burrs and cutting burrs differ significantly from one another [11]. In comparison to cutting burrs, diamond burrs have mean noise levels that are 5–11 dB lower. The burr’s size has the strongest impact on noise levels of all the factors. The noise decreases with decreasing burr size; a 2 mm diamond burr reduces noise at 8 kHz by 20 dB. All of the other factors have negligible effects on the noise levels generated compared to the burr size. In the investigation by Tos et al., most of the surgery was performed using a small diamond burr; it is unlikely that this produced a noise loud enough to harm the contralateral cochlea. Second, Tos et al. assessed hearing using pure tone and speech audiometry up to just 8000 Hz, and this was carried out three months following surgery. Since frequencies beyond 8000 Hz were not employed, a change in higher frequencies could not be detected, making the detection of a transient threshold shift unlikely [10]. This is similar to our study since we didn’t evaluate the higher frequencies that are more than 8000 Hz on PTA.

25 patients with unilateral COM posted for mastoidectomy and tympanoplasty who met the inclusion criteria were enrolled in a study by Jerath and Raghavan. They noticed that there had been no postoperative alteration in the bone-conduction thresholds in the ear on the opposite side. The signal-to-noise ratio of TEOAE at all frequencies did, however, noticeably deteriorate in the postoperative period. They came to the conclusion that drill noise has statistically significant effects on the inner ear function in the contralateral ear as measured by TEOAE, but that PTA cannot detect those effects [1].

In contrast, hearing loss happened more frequently and more severely in individuals with drilling times of less than three hours, according to a research by Palva and Sorri on the non-operated ears of patients who had had simple or radical mastoidectomy. In our circumstances, the average drilling time came out to 39 min. In a study by Da cruz et al., drill noise levels were not affected by irrigation during procedure [13].

By observing changes in the DPOAEs’ amplitudes before and after ear surgery, Da Cruz et al. investigated drillinduced hearing loss in the unoperated ear. Only 2 out of a total of 12 patients had OHC dysfunction owing to an intraoperative temporary drill [13]. DPOAE cannot be evaluated because we only employed pure tone audiometry in our current study.

Conclusion

Based on the monitoring of patients up to one month after surgery, the study found no significant difference in the mean value of Pure Tone Audiometry (PTA) before and after the mastoidectomy when considering air conduction, bone conduction, and air-bone gap in the contralateral ear. However, a definite temporary threshold shift was demonstrated, suggesting that there may be some damage to the outer hair cells caused by drill noise during the mastoidectomy. This damage was not significant enough to be detected by PTA, and more accurate audiological investigations such as otoacoustic emissions would be needed to confirm the hearing loss.The study highlights the importance of considering potential hearing damage caused by drill noise during mastoidectomy, especially for patients with a low cochlear reserve and those who require repeated or multiple surgeries involving drilling the temporal bone. To establish a definitive cause-and-effect relationship, larger studies with other audiological investigations, such as otoacoustic emissions, are recommended.

Limitations

The primary limitation of this study is its smaller sample size, which may have affected the accuracy and generalizability of the results. Conducting the research with a larger sample size could lead to more robust and reliable findings.

Funding

None.

Declarations

Conflict of Interest

None.

Ethical Clearance

Yes.