Residual Hearing Preservation After Cochlear Implantation via Round Window or Cochleostomy Approach

The Laryngoscope VC 2014 The American Laryngological, Rhinological and Otological Society, Inc. Residual Hearing reservation After Cochlear Implantation via Round Window or Cochleostomy Approach Chuan-Hung Sun, MD; Chuan-Jen Hsu, MD, hd; eir-rong Chen, MD; Hung-in Wu, MD, hd Objectives/Hypothesis: The purpose of the study was to investigate whether cochlear implantation using the round window approach provided better preservation of residual hearing than the cochleostomy approach. Study Design: Case-control study. Methods: We designed a case-control study including 40 patients from a tertiary referral center who underwent cochlear implantation surgeries using devices from MED-EL Co., Innsbruck, Austria. Between November 2013 and July 2014, we prospectively enrolled 20 subjects for cochlear implantation surgery using the round window insertion approach. In addition, 20 age- and sex-matched control subjects from the database of cochlear implantees treated using the cochleostomy approach between January 2008 and October 2013 were retrospectively enrolled. The residual hearing of the operated ear was measured before and after surgery. The variables analyzed were the pure-tone average threshold at 250, 500, and 1,000 Hz and the residual hearing at frequencies of 250 to 8,000 Hz. The residual hearing was considered as preserved when the audiometric changes were <10 db hearing loss for each variable. The audiological results of the two groups were compared. Results: No statistically significant difference in the preservation of residual hearing was found in the two groups ( >.05 for all of the variables). Conclusions: The round window and cochleostomy approaches for cochlear implant surgery may preserve residual hearing at similar rates across a range of frequencies. Key Words: Cochlear implantation, hearing preservation, cochleostomy, round window approach. Level of Evidence: 3b Laryngoscope, 125:1715 1719, 2015 INTRODUCTION Recently, new concepts regarding eligibility for a cochlear implant have been established due to advances in implant design and improvements in surgical techniques. 1 Cochlear implantation is now performed in patients of a wide range of ages and with varying degrees of hearing loss. The traditional belief is that for patients with profound hearing loss, preserving residual hearing may not be an issue. 2 reserving residual hearing has been more highly emphasized for patients with hearing loss in the low- and midrange frequencies, 3 but studies have shown that preserving the residual hearing in the implanted ear is a realistic goal for many patients with high-frequency hearing loss. 4 Moreover, the degree of hearing preservation may be closely related to the From the Department of Otolaryngology (C.-H.S.,.-R.C.), Buddhist Tzu Chi General Hospital, Hualien, Taiwan; Department of Otolaryngology (C.-J. H., H.-.W.), Taichung Tzuchi General Hospital, The Buddhist Tzuchi Medical Foundation, Taichung, Taiwan; and the School of Medicine (C.-J.H.,.-R.C., H.-.W.), Tzu Chi University, Hualien, Taiwan. Editor s Note: This Manuscript was accepted for publication December 8, 2014. This study was supported by a grant (TTCRD102-04) from Taichung Tzuchi Hospital, Buddhist Foundation. The authors have no other funding, financial relationships, or conflicts of interest to disclose. Send correspondence to Hung-in Wu, MD, Department of Otolaryngology, Taichung Tzuchi General Hospital, The Buddhist Tzuchi Medical Foundation, No. 66, Sec. 1, Fongsing Rd., Tanzih Township, Taichung City 427, Taiwan. E-mail: hungpin_wu@yahoo.com.tw DOI: 10.1002/lary.25122 degree of electrode insertion trauma. 5 Because the goal of all types of cochlear implant surgery should be to minimize the trauma from electrode insertion, preserving hearing and protecting auditory structures are relevant for all patients, particularly for young children, who have a longer post-treatment life expectancy and a higher likelihood of benefiting from future therapies. Several factors are believed to influence the preservation of residual hearing, which can be broadly divided into environment, electrode design, and surgical technique. The activation of systemic immunity leading to hair-cell apoptosis, including inflammation and oxidative stress, has been shown to negatively affect hearing preservation in animal models. 6 Inappropriate electrode designs, in terms of the curve, width, and length, can cause trauma to the apical turns of the cochlea and lead to poorer hearing preservation outcomes. 7 11 In terms of surgical technique, the drilling procedure required for a standard cochleostomy may damage the endosteum and basal structure of the cochlea, resulting in the total loss of residual hearing. The atraumatic round window (RW) insertion of cochlear electrodes has been considered a better solution for residual hearing preservation. 12 No studies have directly compared the residual hearing levels attained using the two surgical insertion techniques. A few studies have shown independent results obtained using each surgical technique, but no conclusive data have been obtained because no comparative studies have been performed. Therefore, we conducted this study to investigate whether the RW approach might provide 1715

better preservation of residual hearing than the cochleostomy approach. MATERIALS AND METHODS Study Design This study was a case-control investigation that was conducted with the approval of the research ethics committee (REC 102-1) of our facility. Experimental Design The subjects were enrolled in the study at a tertiary referral center. Twenty subjects were prospectively recruited for cochlear implantation via the RW approach between November 2013 and July 2014. Twenty age- and sex-matched control subjects from the database of cochlear implantees treated using the cochleostomy approach between January 2008 and October 2013 were retrospectively enrolled. The enrolled subjects met the following inclusion criteria: receiving a MED-EL (Innsbruck, Austria) implant equipped with a Standard or a FLEX SOFT electrode (both are 31.5 mm in length); full insertion via the cochleostomy or RW approach; preoperative three-frequency pure-tone average (TA) hearing at 250 Hz, 500 Hz, and 1,000 Hz of better than 75 db; and a type A tympanogram. atients with a congenital cochlear malformation, otitis media, other neurological disorders, the recent use of ototoxic medications, liver or renal dysfunction, or pregnancy were excluded. A battery of neuro-otological tests, laboratory studies, and imaging studies, including temporal bone computed tomography and magnetic resonance imaging were performed for all of the subjects. Surgical Techniques Cochleostomy approach. A simple mastoidectomy was performed first, and the middle ear was approached via a posterior tympanotomy. Then, a cochleostomy slightly anteriorinferior to the RW was carefully performed using a drill. When the endosteum was exposed, a Rosen needle was used to advance undercover with a film of hyaluronic acid. Finally, the electrode was slowly inserted. RW approach. A simple mastoidectomy and posterior tympanotomy were performed as for the cochleostomy group. Then, the bony overhang (the RW niche) was identified and removed, using a diamond bur, to expose the RW membrane (RWM). The Rosen needle was used to incise the RWM undercover with a film of hyaluronic acid. Finally, the electrode was inserted. All surgeries were performed by the same surgeon. The subjects in both groups were given a single dose of dexamethasone (8 mg/2 ml) 1 hour before the surgery. Data Collection and Analysis Demographic information for the subjects, including age, gender, laterality, electrode type, current medical status (diabetes mellitus or hyperlipidemia) and laboratory data, including C-reactive protein level and erythrocyte sedimentation rate, were obtained preoperatively. reoperative and postoperative (3 months after the surgery, without the aid of the cochlear implant) audiograms were collected. Three-frequency TA hearing was defined as the average hearing at the frequencies of 500, 1,000, and 2,000 Hz. Low-tone TA hearing refers to average hearing at 250 and 500 Hz, mid-tone TA hearing refers to average hearing at 1,000 and 2,000 Hz, and high-tone TA 1716 hearing refers to average hearing at 4,000 and 8,000 Hz. Residual hearing was considered to be preserved when the audiometric changes were <10 db hearing loss for each variable. The level of postoperative dizziness between patients treated using the two modalities was also compared. The TA hearing levels and the values for the variables were analyzed using nonparametric tests and v 2 tests. The results were expressed as the mean values and standard deviations. The criterion for statistical significance was <.05. RESULTS A total of 40 subjects were included in the study; demographic data for the cochleostomy and the RW groups are shown in Table I. The average preoperative TA data showed no significant differences, and when the TA data were subdivided into the high-, mid- and low-tone averages, no significant differences were found. ostoperative TA at the low tone (250 and 500 Hz), mid-tone (1,000 and 2,000 Hz), and high tone (4,000 and 8,000 Hz) frequencies were recorded and compared with the preoperative TA data within each group (Fig. 1). The postoperative TA data showed worsening of the hearing in each group, but none of the changes were statistically significant. The level of hearing deterioration at the various frequencies in these two groups is shown in Figure 2. The level of hearing deterioration in the RW group was lower at all frequencies compared with the cochleostomy group. However, no significant differences were found. The rates of successful hearing preservation in the two groups were 65% (cochleostomy, n 5 13) and 80% (RW, n 5 16) ( 5.471 (Table II). To evaluate clinical factors that may have affected hearing outcomes, the hearing- TABLE I. Demographic Information for the Cochleostomy and the Round Window Groups. Cochleostomy, n 5 20 Round Window, n 5 20 Age, yr 34.4 6 13.8 33.2 6 15.3.745 Sex (male:female) 08:12 08:12 1.0 Ear (left:right) 10:10 9:11.755 Standard:FLEX SOFT 11:9 7:13.500 ostoperative dizziness 7 (35%) 6 (30%).739 Diabetes 3 (15%) 2 (10%).637 Hyperlipidemia 1 (5%) 3 (15%).298 C-reactive protein, mg/dl 0.19 6 0.18 0.21 6 0.20.654 ESR 4.4 6 2.2 3.1 6 2.5.063 EVAS 7 (35%) 6 (30%).739 reoperative TA, db 70 6 4.8 69.5 6 5.6.967 reoperative low-tone 65.7 6 5.7 65.6 6 7.1.773 TA, db reoperative mid-tone 87.5 6 5.9 86 6 4.4.298 TA, db reoperative high-tone TA, db 98 6 9.5 94.8 6 6.5.149 aqueduct syndrome; TA 5 pure-tone average; SD 5 standard

Fig. 1. Average preoperative (re op) and postoperative (ost op) pure-tone average (TA) in each surgical technique at different frequency levels. RW 5 round window. preserved and nonpreserved groups were compared. No differences pertaining to the surgical approach or other variables were found, except for the use of different electrodes (Standard vs. FLEX SOFT; MED-EL Co., 5.03) (Table III). The data for the groups that received the Standard and the FLEX SOFT electrode were compared (Table IV). None of the values for the variables studied were significantly different between these two groups. The audiometry data for these two groups were analyzed (Table V). The levels of hearing preservation in the Standard and FLEX SOFT groups were significantly different ( 5.032). DISCUSSION According to our results, cochlear implantation via the cochleostomy and RW approaches both preserved residual hearing, with preservation rates of 65% and 80%, respectively. The overall complete hearingpreservation rate reported in previous studies was between 55% and 97% (average TA deterioration of 10 db at 250, 500, and 1,000 Hz). 3,13 15 In a recent systemic review, Havenith et al. 13 compared the cochleostomy and RW approaches in terms of the preservation of residual hearing. There was no benefit of one surgical approach over the other, and the rate of complete hearing preservation ranged from 0% to 40% for the cochleostomy group and from 13% to 50% for the RW group. However, the methodological quality of the studies was poor, and possibly influential factors were not well controlled. Several disadvantages of a cochleostomy, such as the presence of bone dust, the possibility of acoustic trauma during the drilling process, and the higher risk of electrode insertion into the scala vestibule have been discussed. A cochleostomy performed using a soft technique appears to yield fair results. A soft technique that carefully preserves the endosteum during the drilling process, after which the electrode is advanced into the scala tympani, may cause fewer traumas. In a temporal bone study, Briggs et al. 16 compared the two insertion techniques and showed no signs of histological damage to the modiolus, osseous spiral lamina, or basilar membrane. Therefore, we believe that atraumatic surgery is the key to residual-hearing preservation rather than the use of different surgical approaches. In our study, the only variable that affected residual hearing preservation was the use of different electrodes (Standard or FLEX SOFT). The rates of complete hearing preservation in the two groups were 55.6% (Standard) and 86.4% (FLEX SOFT) ( 5.032). The TABLE II. Hearing Deterioration Levels at Various Frequencies in the Cochleostomy and Round Window Approach Groups. Cochleostomy, No. (%), n 5 20 Round Window, No. (%), n 5 20 Fig. 2. Level of hearing deterioration at various frequencies in the two groups. TA 5 pure-tone average; RW 5 round window. TA deterioration 20 db 16 (80) 19 (95).157 TA deterioration 15 db 16 (80) 18 (90).382 TA deterioration 10 db 13 (65) 16 (80).471 TA improvement 10 db 0 0 TA 5 pure-tone average. 1717

TABLE III. Differences in the Hearing reserved and Nonpreserved Groups. reserved, n 5 29 Nonpreserved, n 5 11 Age, yr 33.9 6 13.8 33.5 6 12.9.952 Sex, male:female 12:17 4:7.8 Ear, left:right 13:16 6:5.587 Standard:FLEX SOFT 10:19 8:3.03 ostoperative dizziness 8 (27.5%) 5 (45.5%).287 Diabetes 4 (13.8%) 1 (9.1%).692 Hyperlipidemia 3 (10.3%) 1(9.1%).907 C-reactive protein, mg/dl 0.22 6 0.21 0.15 6 0.11.394 ESR 3.9 6 2.6 3.45 6 1.97.783 EVAS 10 (34.5%) 3 (27.3%).668 reoperative TA, db 69.9 6 4.8 69.4 6 6.1.914 reoperative low-tone TA, db 65.8 6 6.2 65.5 6 6.2.771 reoperative mid-tone TA, db 86.6 6 4.6 87.1 6 6.8.951 reoperative high-tone TA, db 96.1 6 7.2 97.3 6 10.7.796 Cochleostomy:round window 13:16 7:4.294 Except for different kinds of electrodes, all other variables including surgical technique were of no statistical difference. aqueduct syndrome; TA 5 pure-tone average; SD 5 standard Standard and FLEX SOFT electrodes are both 31.5 mm in length and are suitable for full insertion into a completely partitioned cochlea. The major difference between these two electrodes is the diameter of the apical end (Fig. 3). The diameter of the FLEX SOFT electrode is 1.3 mm at the basal end and 0.4 mm at the TABLE IV. Comparison of ossible Influences Between the Two Groups That Received Standard and Flex Soft Electrodes. TABLE V. Comparison of TA Deterioration Levels Between atients Who Received Standard and Flex Soft Electrodes. Standard, No. (%), n 5 18 FLEX SOFT, No. (%), n 5 22 TA deterioration 20 db 15 (83.3) 20 (90.9).477 TA deterioration 15 db 14 (77.8) 20 (90.9).253 TA deterioration 10 db 10 (55.6) 19 (86.4).032 TA improvement 10 db 0 0 The complete hearing preservation rate was significantly higher in the FLEX SOFT group ( 5.032). TA 5 pure-tone average. apical end and 0.5-mm in length, which is thinner at the apical end than the Standard electrode. Deep insertions provide complete cochlear coverage and allow stimulation in a larger frequency range compared with shallow insertions. However, deep insertion of a larger electrode may cause trauma because the diameter of the scala tympani gradually decreases toward the apex. When a larger electrode array is passing through the narrow pathway of the scala tympani, greater force can be produced against the wall. Trauma caused by inserting the array leads to several types of injuries, as observed in specimens of human temporal bone, including perforation of the basilar membrane, fracture of the osseous spiral lamina, and trauma to the lateral wall and the stria vascularis. 17 Moreover, the other characteristic difference in the electrodes is that the FLEX SOFT electrode has five individual unpaired contacts on the apical end, whereas the Standard electrode array has individual paired contact points on the apical end. This feature of the apical end of the FLEX SOFT electrode may increase its flexibility and is thought to decrease the force needed for its insertion. Standard, n 5 18 FLEX SOFT, n 5 22 Age, yr 31.3 6 10.5.505 Sex (male:female) 8:10 8:14.6 Ear (left:right) 9:9 10:12.777 Cochleostomy:RW 11:7 9:13.209 ostoperative dizziness 5 (27.7%) 8 (36.6%).569 Diabetes 2 (11.1%) 3 (13.6%).812 Hyperlipidemia 2 (11.1%) 2 (9.1%).834 C-reactive protein, mg/dl 0.16 6 0.13 0.20 6 0.17.324 ESR 3.56 6 2.4 3.9 6 2.5.64 EVAS 5 (7.7%) 8 (36.6%).569 reoperative TA, db 70.1 6 4.2 69.5 6 5.9.857 reoperative low-tone TA, db 65.6 6 4.3 65.8 6 7.46.378 reoperative mid-tone TA, db 88.2 6 5.06 85.6 6 5.11.173 reoperative high-tone TA, db 97.6 6 9.7 95.3 6 6.8.477 No variable shows a difference between two groups. aqueduct syndrome; RW 5 round window; TA 5 pure-tone average. Fig. 3. Differences of the two electrodes. The apical end of the FLEX SOFT electrode, the FLEX- Tip, is thinner in diameter and a total of 5 mm in length. The FLEX-Tip has a line of single electrode contacts, and the Standard electrode array is lined with pairs of electrode contacts. Image courtesy of MED-EL Co., Innsbruck, Austria. 1718

When discussing hearing preservation, the electroacoustic system (EAS) electrode is often mentioned. The EAS electrode is shorter and covers only the basal area of the cochlea. This characteristic promises postimplantation hearing in low frequencies, which could be amplified by the acoustic system. However, for those patients with poor hearing in low frequencies, the dual system could provide limited benefit. Our current criteria for hearing preservation using the EAS electrode is a TA average better than 65 db at 250 and 500 Hz. When low-tone average reaches 50 db to 65 db, the decision to use an EAS electrode or standard length electrode should be discussed with the patient. This is because the depth of insertion is not a critical determinant of successful hearing preservation. 18 20 Deep insertion also has the advantage of ensuring complete cochlear coverage in the event that residual hearing deteriorates over time or if hearing preservation is not successful. 18 In our study, the overall complete hearing preservation rate in all technique is 72.5% (n 5 29/40), which is comparable to a previous full-insertion study. 21 Because this is the first comparative study of the outcomes of cochlear implantation via the cochleostomy and RW approaches regarding residual hearing preservation, we had a limited number of subjects. Although the study showed no significant difference between the two surgical approaches, the rate of complete hearing preservation in the cochleostomy group was lower (65%). The result may be due to the cochleostomy group having a higher percentage of Standard electrode users (55%, n 5 11/20) than the RW approach group (35%, n 5 7/20), even though there was no statistical difference. Because differences in surgical approaches was our primary end point, there was no specific criteria in the choice of electrode type. The choice of each electrode used in the RW approach group was discussed with the patient s family because of the range of prices. For the retrospectively obtained subjects using the cochleostomy approach, only age and sex were controlled. Nevertheless, more evidence-based and mechanistic studies should be conducted to evaluate the effects of the different electrode designs. CONCLUSION The RW and cochleostomy approaches for cochlear implant surgery may preserve residual hearing at similar rates across a range of frequencies. 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