Impianto uditivo al tronco encefalico: indicazioni e controindicazioni

INTRODUCTION AND OBJECTIVES: Auditory brainstem implants (ABI) have been developed in Losa Angeles at House Ear Institute in 1979 for auditory rehabilitation of patients affected by Neurofibromatosis type 2 (NF2). In NF2, a rare disease with autosomal dominant inheritance, the patients typically suffer from multiple central nervous system tumors and specifically bilateral vestibular schwannomas causing bilateral deafness. If the cochlear nerve is preserved during tumor removal a cochlear implant can be performed. Without this nerve the only hearing rehabilitation in these patients could be via an Auditory Brainstem Implant. The number of ABI users has been increasing over the years and one would expect that the outcomes with an ABI would be progressively increase also. But a rising number of ABI user is not equivalent to a better result, as the main indication (NF2) embraces more than just the placement of an implant. Recently there has been growing number of indications to ABI other than NF2 (bilateral cochlear ossification, major malformation of the inner ear, aplaasia or severe dysplasia of the cochleovestibular nerve bundle, far advanced otoscleorsis, bilateral cochlear trauma) and reports on the use of an ABI in non tumor patients are growing. The aim of this study was to assess the ABI outcomes in NF2 and non NF2 patients at our center, discuss the pre-, peri- and postoperative care and the available therapeutic options. PATIENTS AND METHODS: The charts of all patients that received an ABI at the Gruppo Otologico, an Italian tertiary referral skull base center, have been retrospectively reviewed. RESULTS: 27 patients have been implanted with an ABI; 24 patients suffered from NF2 and 3 had nontumor indications. Of the 24 patients, 19 use their ABI on a daily basis, 4 are non users and 1 died of NF2 progression; 8 patients out of 19 users showed at least some speech discrimination. Mean age was 35 years old (range 18-69) and mean tumor diameter was 3 cm. In the small group of three non NF2 patients (bilateral cochlear ossification in all cases), 2 are daily user (one reched 100% speech discrimination and the other patient with associated blindness achieved detection of sound) while the remaining patient never showed any benefit from ABI. DISCUSSION Auditory brainstem implantation in NF2 directly after tumor removal is a safe procedure and the best means of hearing rehabilitation if the cochlear nerve is not preserved. Also non-tumor patient may be successfully implanted with ABI if cochlear structures and nerves are compromised. The results in NF2 and in non NF2 cases in these series are poor compared to cochlear implantation still the majority of the patients have benefit of the implant during daily life particularly in combination with lip-reading. CONCLUSIONS Although the results of brainstem implantation are unpredictable, some patients achieve open-set speech discrimination and even telephone use. Due to the unpredicable results, the rehabilitation of choice should be a cochlear implant but therefore a functional and intact cochlear nerve is necessary.