Orginal Paper Audiology Neurotology
Audiol Neurotol 2007;12:165–169 DOI: 10.1159/000099019
Received: July 19, 2006 Accepted after revision: October 23, 2006 Published online: January 25, 2007
Residual Hearing Thresholds in Cochlear Implantation and Reimplantation Walter Di Nardo Italo Cantore Francesca Cianfrone Pietro Melillo Mario Rigante Gaetano Paludetti Institute of Otorhinolaryngology, Catholic University of the Sacred Heart, Rome, Italy
Key Words Cochlear implant Cochlear reimplantation Residual hearing
Abstract Implant and reimplantation surgery should be carried out with preservation of residual hearing. The aim of this study is to evaluate the effects of such a surgery on hearing threshold. We report the results on 40 patients, 20 males and 20 females, aged between 5 and 70 (mean 29) years, 16 pre-verbal and 24 post-verbal, with measurable pre-operative auditory thresholds. We used the following implants: Advanced Bionics, Med-El, Cochlear, and MXM Digisonic. Four of the patients underwent cochlear reimplantation owing to device failure. A complete insertion was obtained in all patients. Responses to pure-tone stimuli were evaluated in each ear in pre-implant conditions and 3 months after cochlear implant or reimplantation. The explantation was performed with minimal cochlear trauma and preservation of the explanted electrode integrity. 35% showed no change of the hearing threshold, 45% showed a slight worsening of the hearing threshold level in the implanted ear, and 20% had a total loss of residual hearing. Median increases of threshold levels were 10, 5, 10 and 3 dB HL respectively for 125, 250, 500 and 1 kHz. In the group of 4 patients who underwent cochlear reimplantation, 2 showed no variation of the hearing
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threshold, 1 preserved an appreciable hearing threshold, and 1 had a total loss of residual hearing. The data seem to suggest that hearing function is rather resistant to mechanical trauma during implant and reimplant surgery; the authors hypothesize a role for direct spiral ganglion activation under intense mechanical stimulation. Copyright © 2007 S. Karger AG, Basel
Introduction
Presently, cochlear implants constitute the mainstay of treatment for severe, profound hearing loss. Cochlear reimplantation also showed a similar efficacy [Alexiades et al., 2001]. Factors influencing the preservation of residual hearing following cochlear implantation or reimplantation are still a matter of debate. Cochlear implant surgery can have a wide range of effects on inner ear anatomic structures, including fracture of the osseous spiral lamina, damage to the stria, the spiral ligament and the organ of Corti, alterations of intracochlear physiologic ionic equilibrium and formation of a fibrous sheath enveloping the array. The explantation procedure is carried out with minimal cochlear trauma and preservation of the explanted electrode integrity. Brimacombe et al. [1994], Rizer [1988] and Kiefer et al. [1999] reported a post-implantation loss of residual
Dr. Italo Cantore, MD Institute of Otorhinolaryngology, ‘A. Gemelli’ University Hospital Catholic University of the Sacred Heart L.go A. Gemelli 8, IT–00168 Rome (Italy) Tel. +39 06 3015 4439, Fax +39 06 3051 194, E-Mail
[email protected]
12 10 8
dB
hearing in the vast majority of implanted patients. A partial preservation of residual hearing after cochlear implantation was reported by Hodges et al. [1997], Dye et al. [1987], Skarzynski et al. [2002], and in a recent multicenter European study [James et al., 2005]. In contrast, Webb et al. [1988] and Clark et al. [1988] accomplished the insertion of electrodes with minimal histopathological trauma to intracochlear structures, including neural elements. To our knowledge, no studies have been published so far dealing with residual hearing in cochlear reimplantation.
6 4 2 0
125
250
500
1000
Hz
Fig. 1. Median threshold worsening after implantation for each
Materials and Methods We studied 40 patients, 20 males and 20 females, aged between 5 and 70 (mean 29) years, with measurable pre-operative hearing thresholds. 16 of them were pre-verbal and 24 post-verbal. Of these patients, 4 (2 males and 2 females) underwent cochlear reimplantation because of device failure. The surgery protocol we followed was minimally invasive, so that a satisfactory aesthetic result could be obtained and trauma to the inner ear structures could be limited. The surgical procedure included a retroauricular incision, mastoidectomy, posterior tympanotomy and a 1.2-mm cochleostomy performed anteriorly and inferiorly to the round window. We counted the array rings remaining outside the cochleostomy in order to evaluate insertion depth. Before wound closure, electrode impedance measurements, neural response telemetry and x-rays were performed in order to check the implant integrity and its correct position. The explantation procedure caused minimal cochlear trauma and preserved the electrode integrity. The reimplanted electrode in each case was of the same type as the explanted one (2 Cochlear, 1 Advanced Bionics, 1 MXM Digisonic). Responses to pure-tone stimuli were measured in each ear in pre-implant conditions and at a minimum of 3 months after surgery. Patients received pre- and post-implantation audiometric testing which was performed with an Amplaid 319 type 1-IEC 645 audiometer with associated specific earphones, calibrated according to ISO 389 and American National Standards Institute (ANSI) and with maximum outputs at 125, 250, 500, 1000, 2000, 4000 and 8000 Hz of 85, 105, 120, 125, 125, 125 and 105 dB HL respectively. Frequencies 11 kHz were not considered because only few subjects had measurable hearing. We assumed that no change of threshold after implantation occurred when worsening was !5 dB in a maximum of two frequencies. With regard to statistical analysis, we used the median because it eliminates the need to assign a numerical value in the frequent cases in which the hearing threshold exceeds the limit of audiometer output, and also the mean calculation to evaluate the hearing threshold worsening because the median calculation leads to underestimate the real values. Moreover, the mean also allowed us to better outline the indicative threshold shift. Therefore, for mean calculation we used values 5 dB above the maximal audiometer emissions for each frequency for which no threshold was available (values in parentheses in tables 1 and 2).
166
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studied frequency in all 40 patients.
Results
Of the 40 patients studied, 14 (35%) showed no variation of the hearing threshold, 18 (45%) showed a worsening of hearing threshold level in the implanted ear, and 8 (20%) had a total loss of residual hearing (table 1). Median increases in hearing threshold levels were 10, 5, 10 and 3 dB respectively for 125, 250, 500 and 1 kHz (fig. 1). Mean increases in hearing thresholds were 11, 12, 13 and 11 for the same frequencies. In the group of 4 patients who underwent cochlear reimplantation, 2 showed no variation of the hearing threshold in the reimplanted ear, 1 maintained an appreciable hearing threshold level, and 1 had a total loss of residual hearing (fig. 2, table 2).
Discussion
Factors having a role in the potential preservation of residual hearing following cochlear implant and reimplantation are still a matter of debate. Lehnhardt [1993] was the first to describe a ‘soft surgery’ to be performed with a minimal 1.2-mm diameter cochleostomy on the anterior and inferior lip of the round window niche, an endosteal incision with micro-lancet, and a gentle and limited electrode insertion, during which Healon was used in order to lubricate the electrode and the cochleostomy was sealed. The aim was to minimize damage to the inner ear, so that better hearing results could be obtained [Lehnhardt et al., 1994; Cohen, 1997]. Several studies report that residual hearing can be preserved even when an electrode array is placed into the scala tympani. Insertion depth seems to play a role in reDi Nardo/Cantore/Cianfrone/Melillo/ Rigante/Paludetti
Table 1. Residual hearing before and after surgical procedure in the implanted patients
Patient
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40
Sex
Age
M F M M F M F F F F M F M M F M M M F M M F M F M F M M F F F F M F M M F F F M
Implant
40 40 28 28 27 15 26 6 25 13 31 62 55 30 44 26 13 16 41 36 30 32 70 51 33 15 18 6 40 29 56 24 10 6 34 36 9 61 9 5
Side
Cochlear CI 22 M Cochlear CI 22 M Cochlear CI 22 M Cochlear CI 22 M Cochlear CI 24 M Clarion AB-5100H Clarion AB-5100H Cochlear N24C Med-El Combi 40+ Clarion AB-5100H Clarion AB-5100H Clarion AB-5100H Clarion AB-5100H Clarion AB-5100H Med-El Combi 40+ Clarion AB-5100H Med-El Combi 40+ Cochlear N24C Med-El Combi 40+ Cochlear N24C Cochlear N24C Cochlear N24C MXM Digisonic DX10/C Cochlear N24C Cochlear N24C Cochlear N24C Cochlear N24C Cochlear N24C Cochlear N24C Cochlear N24C Cochlear N24C Cochlear N24C Cochlear N24C Cochlear N24C MXM Digisonic DX10/C Cochlear N24C Cochlear N24C Cochlear N24C Cochlear N24C Clarion HiRes 90k/HiFocus
left left right left right right right right right right right right right right right right right right right right right right left left right right left left right right left right left right right right left left right left
Before implantation
After implantation
125
250
500
1000
125
250
500
1000
(90) (90) 80 80 80 75 80 (90) 70 80 70 (90) (90) 80 70 85 70 75 80 60 90 55 80 55 85 (90) 70 (90) 30 75 20 70 85 75 70 85 80 45 80 85
105 100 90 90 90 90 90 90 80 90 80 100 105 85 105 100 80 75 95 60 100 65 85 75 90 85 105 95 70 95 15 85 85 80 85 105 90 75 105 95
115 105 105 95 90 115 100 100 85 110 95 110 (125) 100 115 105 75 100 110 85 110 90 110 80 110 95 115 100 90 105 40 85 105 95 105 (125) 105 75 110 95
110 110 110 100 110 115 110 105 100 (130) 100 130 115 110 130 (130) 110 105 105 100 110 90 110 105 110 100 110 110 100 110 100 90 105 100 105 (130) 115 90 (130) 120
(90) (90) (90) (90) (90) 85 (90) (90) 85 85 (90) (90) (90) (90) 75 (90) (90) 80 85 80 (90) 85 85 (90) 80 (90) 75 (90) (90) 85 0 (90) 85 85 85 85 85 85 85 85
105 100 (110) (110) (110) 100 100 90 95 115 (110) (110) 105 (110) 105 100 (110) 75 95 85 (110) 90 90 75 90 105 105 100 (110) 105 55 95 90 95 95 105 100 95 105 95
120 110 (125) (125) (125) 115 110 100 110 120 (125) (125) (125) (125) 115 110 (125) 100 110 105 (125) 110 110 80 115 115 115 120 (125) 120 80 100 105 100 115 (125) 105 105 115 95
110 110 (130) (130) 120 120 130 110 115 120 (130) (130) 115 (130) 130 130 (130) 110 115 120 (130) 120 110 110 (130) 105 115 130 (130) 130 110 95 105 110 120 (130) 120 110 (130) 120
Values in parentheses represent thresholds above the maximal audiometer emission.
Table 2. Residual hearing before and after surgical procedures in the reimplanted patients
Patient
1 2 3 4
Sex
M F F M
Age
36 40 26 34
Implanted side
right right right right
Residual Hearing Thresholds in Cochlear Implantation and Reimplantation
Before implantation
After implantation
After re-implantation
125
250
500
1000
125
250
500
1000
125
250
500
1000
60 30 80 70
60 70 90 90
85 90 100 105
105 110 105 105
80 (90) (90) 80
100 110 100 100
110 105 110 110
120 120 (130) 120
80 (90) (90) 80
100 110 (110) 100
115 115 (125) 115
120 120 (130) 120
Audiol Neurotol 2007;12:165–169
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Fig. 2. Audiograms representing the threshold worsening after implantation and reimplantation procedures for
the 4 reimplanted patients of the study.
sidual hearing preservation. It appears that insertion angles 1 400° impact hearing preservation at frequencies of 250–500 Hz. Kiefer and Gstoettner [see Gstoettner et al., 2004] obtained residual hearing preservation in 80% of the implanted patients, in agreement with our results, but with worse results as far as hearing threshold levels are concerned (10, 15, 17.5 and 5 dB for frequencies of 125, 168
Audiol Neurotol 2007;12:165–169
250, 500 and 1000 Hz). A remarkable difference stands out if we compare our results with those reported by James et al. [2005] in a multicenter study (23, 27 and 33 dB for 125, 250 and 500 Hz). There are no data in the literature about patients who underwent cochlear reimplantation. It is difficult to comment these results if we consider the undesired sensoriDi Nardo/Cantore/Cianfrone/Melillo/ Rigante/Paludetti
neural hearing losses resulting from much less invasive otosurgical procedures. It is reported that severe sensorineural hearing impairment can occur in 1% of patients who undergo stapes surgery [House et al., 2002]. Cochlear implantation can damage cochlear structures in a variety of ways: fracture of the osseous spiral lamina, alteration of the stria, the spiral ligament and the organ of Corti, disruption of intracochlear physiologic ionic equilibrium and formation of a fibrous sheath surrounding the array [Balkany et al., 1999]. In fact, besides the well-known histopathological data, the fine different ionic composition of the three intracochlear fluid compartments, represented by perilymph, endolymph and tunnel of Corti fluid, may be presumably compromised following array insertion, with consequent serious impairment of the transductional function. Besides, spiral ganglion cells seem to be the least damaged intracochlear sensorineural cellular population. Interestingly, the modest lessening they show does not affect cells adjacent to the electrode array, suggesting that deleterious effects are not due to physical trauma; moreover, electrical stimulation may represent an antidegenerative factor for these cells. It is therefore possible that survival of spiral ganglion cells could be involved in preservation of residual hearing in cochlear implant patients [Khan et al., 2005].
A direct starting of action potentials from spiral ganglion cells in response to high-intensity mechanical stimulations, without a hearing-cell and/or support-cell interaction, could be hypothesized. Further studies on the topic are needed to explain, even in cochlear reimplantation, the surprising data concerning residual hearing preservation despite the invasive procedure needed to insert a cochlear implant.
Conclusions
Preservation of residual hearing following cochlear implant is possible and suggests that inner ear functions are rather resistant to the traumatic effects of such otosurgery. Moreover, the reimplanted patients show a slighter worsening of the residual hearing after the second procedure than after the first implantation. It may be that some ideas concerning cochlear physiology could need revisiting in order to obtain a better insight into the mechanisms of such an amazing function preservation that could be related to direct spiral ganglion fiber activity without hair-cell interaction under intense mechanical stimulation.
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Gstoettner W, Kiefer J, Baumgartner WD, Pok S, Peters S, Adunka O: Hearing preservation in cochlear implantation for electro acoustic stimulation. Acta Otolaryngol 2004; 124: 348–352. Hodges AV, Schloffman J, Balkany T: Conservation of residual hearing with cochlear implantation. Am J Otol 1997;18:179–183. House HP, Hansen MR, Al Dakhail AAA, House JW: Stapedectomy versus stapedotomy: comparison of results with long-term followup. Laryngoscope 2002;112:2046–2050. James C, Albegger K, Battmer R, Burdo S, Deggouj N, Deguine O, et al: Preservation of residual hearing with cochlear implantation: How and why? Acta Otolaryngol 2005; 125: 481–491. Khan AM, Handzel O, Damian D, Eddington DK, Nadol JB: Effect of cochlear implantation on residual spiral ganglion cell count as determined by comparison with the contralateral nonimplanted inner ear in humans. Ann Otol Rhinol Laryngol 2005; 114: 381– 385.
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