Eur Arch Otorhinolaryngol (2001) 258 : 5–8
© Springer-Verlag 2001
O TO L O G Y
Walter Di Nardo · Annarita Fetoni · Susanna Buldrini · Stefano Di Girolamo
Auditory brainstem and cochlear implants: functional results obtained after one year of rehabilitation
Received: 19 September 2000 / Accepted: 28 September 2000
Abstract Very little information has been published on the clinical outcome of auditory brainstem implants (ABI). The present paper evaluates results obtained in a patient affected by a bilateral acoustic neuroma in type II neurofibromatosis who received an implant during removal of the residual tumor. One year later surgical revision of the ABI was necessary because no auditory sensation was obtained after ABI activation. Twelve months after the surgical revision, 12 electrodes out of 15 evoked auditory sensation. The results of rehabilitation were compared with those obtained in a group of eight postlingually deaf patients with cochlear implants (CI). Twelve months postoperatively the CI patients identified 97.7 ± 5.1% of bisyllabic words in a closed set while the ABI patient identified 86%. CI patients recognized 87.1 ± 11.3% of sentences and 81.3 ± 14.8% of words with contextual cues while the ABI patient recognized 75% and 65% respectively. Speech recognition improved more slowly in the ABI patient than in the CI patients and his scores for open-set words and sentences without lip reading and contextual cues were poorer. Although the results obtained in the ABI patient were not as good as those obtained in the CI patients, the ABI patient said his quality of life was improved. Keywords Auditory brainstem implant · Cochlear implant · Speech perception
Introduction An auditory brainstem implant (ABI) is at present the only system able to stimulate the central auditory pathways in patients with deafness due to damage, resection
W. Di Nardo () · A. Fetoni · S. Buldrini · S. Di Girolamo Istituto di Clinica otorinolaringoiatrica, Policlinico A. Gemelli, Università Cattolica del S. Cuore, Largo Agostino Gemelli 8, 00168 Roma, Italy e-mail:
[email protected], Tel.: +39-06-30154439, Fax: +39-06-3051194
or absence of auditory nerves. A multichannel auditory brainstem prosthesis was presented for the first time in Europe in 1991 and was implanted one year later [5]. The current ABI are represented by an array of surface or penetrating electrodes stimulated via transcutaneous transmission. Conceptually ABI is very similar to a multichannel cochlear implant: the only differences are the electrode’s design and the fact that the array of electrodes is placed on the cochlear nucleus complex rather than in the scala tympani. Selection criteria for such implants include an irreversible lesion of both auditory nerves, age older than 12 years, adequate linguistic skills, reasonable expectations concerning the implant results, and the patient’s ability to follow the rehabilitation protocol [9]. In patients with congenital absence of the auditory nerves the age of intervention is obviously lower. In type II neurofibromatosis ABI implantation is carried out at the same time of tumor removal via a translabyrinthine or retrosygmoid approach [2]. During surgery, intraoperative monitoring of the VIIth and IXth nerves is needed and postoperatively electrically evoked auditory brainstem potentials have to be recorded in order to evaluate the correct position of the electrodes on the cochlear nucleus complex. Several reports of experimental work have demonstrated that the ventral cochlear nucleus is tonotopically organized, high frequencies being dorsally represented and low frequencies ventrally represented [8, 13]. As with cochlear implants, the greater the number of electrodes the wider the programming choices, making it possible to activate those electrodes that offer the best performance and exclude those evoking extra-auditory effects [6]. In this paper we describe results obtained almost 12 months after implantation of a brainstem device in a patient with type II neurofibromatosis and eight patients who underwent a cochlear implant.
Patients and methods Eight consecutive postlingually deaf patients aged between 27 and 50 years (mean 35.7 years), in whom the duration of deafness var-
6 Table 1 Demographic data for eight adults with cochlear implants
Patient
Age at implantation (years)
Duration of deafness (years)
Etiology
Cochlear implant
M.L. T.S. A.M. T.G. G.M. T.A. G.E. S.S.
50 30 27 49 39 36 28 27
2 10 15 5 8 4 15 5
Unknown Unknown Unknown Otosclerosis Unknown Unknown Unknown Unknown
Clarion Clarion Clarion Nucleus Nucleus Nucleus Nucleus Nucleus
Fig. 1 The multichannel auditory brainstem implant carrier is a flat plate with 15 electrodes arranged in three rows. Ten months after reimplantation 12 electrodes were activated; only electrodes 1, 2 and 4 remained inactive
ied from 2 to 15 years, received cochlear implants between March 1997 and May 1999 (see Table 1). A 28-year-old patient with type II neurofibromatosis, already operated on elsewhere for a bilateral acoustic neuroma, underwent removal of the residual tumor by a retrosigmoid approach and at the same time a 15-electrode MXM Digisonic ABI was implanted. The electrode function was peroperatively tested by means of an electrically evoked auditory brainstem response recorded by stimulating electrodes 3, 9 and 15. One month later a first cartographic test of the electrodes was performed and somatosensory reactions but no auditory sensations were obtained. In the next two tests the same results were obtained and therefore the implant was not activated. In April 1999 revision surgery was carried out in the ABI patient and the implant was repositioned. All electrodes except two showed a positive integrity test, while clear-cut electrically evoked auditory brainstem responses were obtained with electrodes 15, 3 and 6. In June 1999, 6 out of 15 electrodes were activated; in another five the stimulus needed to evoke auditory sensation was too strong, while no auditory sensation was obtained on stimulating the remaining four electrodes. Ten months later another six electrodes were activated, giving a total of 12 out of 15. Electrodes 1, 2 and 4 remained inactive (Fig. 1). A CT scan (Fig. 2) and cerebral single photon emission computerized tomography was carried out
Fig. 2 Axial computerized tomography scan shows the electrode array implanted in the brainstem on the cochlear nucleus complex
to gain further information concerning about the array position and the areas that could be activated after acoustic stimulation. Both the CI patients and the ABI patient began their rehabilitation immediately after activation of the implants, with sessions taking place twice a week. The preoperative and postoperative evaluation protocols included closed and open-set speech recognition tests. The postoperative assessment was administered at 3-month intervals. After adaptation to environmental sound the patients underwent a series of tests as described by Amigoni et al. [1] and Rossi [11] in order to finally evaluate detection of phonemes, word discrimination, identification of consonants, vowels and bisyllabic words, and recognition of sentences and words in closed and open sets with or without contextual cues. The tests were administered as live-voice presentations using only auditory information. The scores reflect the total number of correctly repeated words. Each new test was begun when at least 50% of the questions raised in the previous easier test had been correctly answered with only auditory information. Rehabilitation in the ABI patient was the same as in the eight postverbal deaf patients who underwent cochlear implants. All data were collected 12 months after activation for both the CI patients and the ABI patient.
7 Table 2 Postoperative speech recognition development (shown as % and SD) for eight patients with a cochlear implant (CI) and one patient with an auditory brainstem implant (ABI)
Test
3 months CI§
Detection of phonemes Words discrimination Bisyllabic identification Sentence recognition* Word recognition* §Mean
100 87.4 83.7 82 74.2
(12.6) (19.8) (13.4) (12.9)
6 months ABI
CI§
100 80 55 30 20
100 93.5 95 83.7 80.7
(8.3) (6.3) (2.1) (7.2)
12 months ABI
CI§
ABI
100 83 70 55 35
100 100 97.7 (5.1) 87.1 (11.3) 81.3 (14.8)
100 100 86 75 65
percentage of correct scores; *speech recognition with contextual cues
Results No postoperative complications were observed in either the CI patients or the ABI patient and therefore the rehabilitation program begun immediately after activation of the implants. All CI patients used the device for the whole day while the ABI one used it for almost 7–8 hours a day. Postoperative speech recognition development based on auditory cues alone is represented in Table 2. Twelve months postoperatively CI patients identified 97.7 ± 5.1% bisyllabic words in a closed set while the ABI patient identified 86%. CI patients recognized 87.1 ± 11.3% of sentences and 81.3 ± 14.8% of words with contextual cues while in the ABI patient the scores were 75% and 65% respectively. Twelve months after activation the ABI patient was unable to perform recognition tests without contextual cues while CI patients were able to perform them with satisfactory scores (72.65 ± 13.00%). Three of the eight CI patients currently communicate via the telephone. The performance of the ABI patient improved after extra electrodes were activated but became worse when the patient was exposed for a long time to a noisy environment or after prolonged daily activation. Both CI patients and the ABI patient reported that their quality of life had improved.
Discussion The literature on functional results in ABI patients is rather scanty. In 1995 Laszig [6] published data concerning the first six ABI patients while Shinet [12] compared data concerning six patients operated on for cerebellopontine angle tumors with VIIIth nerve preservation who received cochlear implants and one patient who received an ABI and concluded that CI patients performed better than ABI patients. The patients described by the Los Angeles Group [10] complained about extra-auditory effects such as tingling in the head and in the back, but all improved their communicative skills, with three patients reaching scores of 49–50% in recognizing words and sentences and using the telephone. A multicentric study performed in Germany and the United Kingdom [7] describes results in 14 out of 17 ABI patients. In 79% of these speech recognition with lip reading was significantly improved; in 36% such im-
provement was present using only the auditory channel and 71% of patients used the device on a day to day basis. All the data in the literature concern results obtained with different devices, mainly the Cochlear Nucleus implant, while no multicenter reports concerning results obtained with MXM Digisonic device have been published. The ABI case we have described needed revision surgery about one year after the first insertion because auditory sensation was absent due to postoperative dislocation of the electrode array. We reached this conclusion because the peroperative EABRs were satisfactory while during activation only somatosensory sensations were reported by the patient. Surgical repositioning led to satisfactory results. In fact our ABI patient after one year of rehabilitation improved his quality of life as he performed well in conversation and was able to live independently due to his improved alarm reaction. Speech recognition improved more slowly in the ABI patient than in CI patients and he had poorer scores mainly for open-set words and sentences without lip reading and contextual cues. Moreover direct stimulation of the cochlear nuclei seems to cause a sort of early fatigue that reduces performance in a noisy environment and shortens the daily activation period (almost 7–8 h a day). Such a finding was not present in our CI patients, who showed results and performances comparable with those reported in the literature for each device [3, 4, 14]. We are aware that ABI and CI data are hardly comparable for several reasons. First of all electrical stimulation of the cochlear nuclei probably evokes auditory sensations very different to those evoked by electrical stimulation of the cochlea. Furthermore the speech decoding strategies of the CI and ABI devices are different (and may even differ in different CI patients). Finally the auditory deprivation period was overall far longer for the CI patients than for the ABI patient. The experience of different groups of workers concerning the functional outcome for ABI patients is rather small and the results of all groups need to be integrated in order to provide more information.
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