Artikel
Electric evoked auditory brainstem responses – Importance for functional outcome in auditory brainstem implant (ABI) surgery
Elektrisch evozierte auditorische Hirnstammpotentiale – ihre Bedeutung für das Funktionsergebnis in der Chirurgie des auditorischen Hirnstamm-Implantats
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Autoren
Veröffentlicht: | 23. April 2004 |
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Gliederung
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Objective
ABI offer a realistic chance to re-establish some useful auditory function in patients with bilateral deafness due to Neurofibromatosis Type 2. Intraoperative functional control of the auditory pathway by neuro-physiological means might be helpful in adequate ABI placement.
Methods
Patient selection is based on NF-2 disease manifestation and psycho-social stability. ABI electrode placement is controlled anatomically and by cranial nerve (VIIth to XIIth) and long tract monitoring. Electrically evoked auditory brainstem responses (EEABR) are evaluated at exposure and stimulation of the cochlear nucleus region. Absence of side effects and reliable EEABR are pre-conditions to definite ABI placement. Postoperative management includes regular control of speech processor programming and audiometric laboratory tests. The quality of auditory function is assigned to classes 1 to 4 based on consonant recognition and speech tracking test at 6 months follow-up.
Results
From 26 patients selected for ABI implantation 24 received an ABI, at tumor surgery (n=20) or thereafter (n=4); all but two experienced auditory sensations and were controlled for at least 6 months follow-up. Two patients showed ABI dislocation and surgical revision was carried out successfully in one and scheduled for the other. Two patterns of EEABR were found, with distinct components III, IV and V in 15 cases and with deformed melted complex in 9 patients. These differences were of predictive importance with regard to functional outcome as class 1 or 2 auditory function were only obtained after distinct EEABR components.
Conclusions
While functional outcome in ABI surgery is dependent on a multitude of pre-existing factors, the only aspect actively to be modified is the adequate microsurgical ABI placement. Obviously, a distinct EEABR recording reflects a useful activation of the cochlear nucleus and hereby allows to predict a sufficient number of electrodes to be activated and to produce good hearing function.