Deafness and the bionic ear.
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Auditory Brain Stem Implants↗
Biomedical subjects
L Sacchetto
Publications and source records attributed to L Sacchetto.
Hearing habilitation with auditory brainstem implantation in two children with cochlear nerve aplasia.
Patients with aplasia and hypoplasia of the cochlear nerve have no chance of having their hearing restored by stimulating the periphery of the auditory system using the traditional cochlear implant. A possible approach to auditory rehabilitation may be direct electrical stimulation of the cochlear nuclei with an auditory brainstem implant (ABI). Recently, two children, aged 4 and 3 years, respectively, with bilateral severe cochlear malformations and cochlear nerve aplasia received an ABI. The present paper reports the technique and the preliminary results of this experience. The classic retrosigmoid approach was used. The correct position of the electrodes was estimated with the aid of EABRs and neural response telemetry (NRT). No postoperative complications were observed. High-resolution CT scans with a bone algorithm reconstruction technique were taken postoperatively to evaluate electrode placement before discharge. The ABI was activated 30 days after implantation in both patients. To date 16 and 13 electrodes, respectively, have been activated in the two children. Three months after activation the first patient had achieved good environmental sound awareness, good speech detection and some speech discrimination. The second child, 1 month after activation, had achieved good environmental sound awareness and moderate speech detection. To the best of our knowledge this is the first report of patients with hypoplasia of the cochlea and aplasia of the cochlear nerve, aged below 5 years and treated with an ABI.
Audiometry↗
Intraoperative monitoring for hearing preservation and restoration in acoustic neuroma surgery.
The present article reports on our experience with hearing preservation during 158 acoustic neuroma (AN) operations via the retrosigmoid-transmeatal (RS-TM) approach with the aid of intraoperative auditory monitoring. Several auditory monitoring methods are described. Of these, the bipolar cochlear nerve action potential (CNAP) was found to be the most helpful in preserving hearing. Of 106 patients with useful hearing preoperatively, more than 50% had useful hearing after surgery. Electrical auditory brainstem responses were useful in the placement of an auditory brain stem implant (ABI) in 4 patients with neurofibromatosis type 2 (NF2). All 4 reported speech perception benefit and use their ABIs regularly in their lives. It is our firm belief that intraoperative auditory monitoring has a pivotal role in the preservation and restoration of hearing in AN surgery.
Journal Article↗
Advantages of the retrosigmoid approach in auditory brain stem implantation.
From April 1997 to December 1999, six patients (five men and one woman), ranging in age from 22 to 37 years with neurofibromatosis type 2 (NF2) were operated on via the classic retrosigmoid-transmental (RS-TM) approach for removal of a vestibular schwannoma (VS) (tumor size from 12 to 40 mm) and for auditory brain stem implantation (ABI). After tumor removal, the floor of the lateral recess of the fourth ventricle and the convolution of the dorsal cochlear nucleos were reached, and the ABI was inserted. More recently, an ABI was implanted via the retrosigmoid approach in a 4-year-old boy with a cochlear malformation (common cavity) associated with cochlear nerve aplasia. Electrically evoked auditory brain stem responses (EABRs) and neural response telemetry (NRT) were performed to verify the correct positioning of the inserted electrodes. No major complications related to ABI were observed. ABI has been activated to date in five of the NF2 patients. Auditory sensations with various numbers of electrodes were evoked in all patients. We consider the RS-TM approach the route of choice for ABI insertion in patients with NF2 and good hearing, offering a chance of hearing preservation, and in patients with complete cochlear ossification, severe head trauma and cochlear fracture, or nerve disruption, or a combination of these. A new indication for ABI implantation via the RS approach is presented by patients with bilateral cochlear nerve aplasia.
Journal Article↗
New approach for cochlear implantation: cochleostomy through the middle fossa.
The middle fossa approach was used in 11 patients with profound bilateral hearing loss for insertion of a cochlear implant. Fibroadhesive otitis media (n = 1), bilateral cavity radical mastoidectomy (n = 1), autoimmune inner ear disease (n = 2), previous cranial trauma (n = 1), genetic prelingual deafness (n = 5), and otosclerosis (n = 1) were the causes of deafness. A cochleostomy was performed on the most superficial part of the basal turn, and the electrode array was inserted up to the cochlear apex. Speech perception tests (1-9 months after cochlear implant activation) yielded better results in these patients compared with a homogeneous group of postlingually deaf patients operated on through the traditional transmastoid route. Insertion of the implant through the middle fossa cochleostomy furnishes the possibility of stimulating areas of the cochlea (ie, the middle and apical turns) where a greater survival rate of spiral ganglion cells is known to occur, with improvement of information regarding the formants relevant for speech perception.
Adolescent↗
Retrosigmoid approach for auditory brainstem implant.
The present paper reports our experience with the surgical retrosigmoid-transmastoid (RS-TM) technique for implanting auditory brainstem implants (ABIs). From April 1997 to August 1998, four patients with neurofibromatosis type 2 (NF2) were operated on for vestibular schwannoma removal with ABI implantation. The subjects (three men and one women) ranged in age from 22 to 31 years. Tumour size ranged from 12 to 30 mm. A classical RS-TM approach was performed. After tumour excision, identification of landmarks (VIIth, VIIIth and IXth cranial nerves, choroid plexus) to the foramen of Luschka was carefully carried out. The choroid plexus was partially removed and the tela choroidea divided and deflected. The floor of the lateral recess of the fourth ventricle and the convolution of the dorsal cochlear nucleus became visible. The electrode array was then inserted into the lateral recess and placed in the correct position with the help of electrically-evoked auditory brain stem responses. Auditory sensations were induced in all patients with various numbers of electrodes. Different pitch sensations could be identified with different electrode stimulation. Details of the results are presented. In our series, the RS-TM approach represents the elective route for ABI insertion.
Adolescent↗
The retrosigmoid approach for auditory brainstem implantation.
OBJECTIVE: To describe our experience with the retrosigmoid-transmeatal (RS-TM) approach in auditory brainstem implantation (ABI) as well as the anatomosurgical guidelines for this route. STUDY DESIGN: Retrospective case review. SETTING: Ear, Nose, and Throat Department of the University of Verona. PATIENTS: Five patients with neurofibromatosis type 2 (NF2) were operated on for vestibular schwannoma removal with ABI implantation from April 1997 to June 1999. The patients were four men and one woman, whose ages ranged from 22 to 37 years. The tumor sizes ranged from 12 to 30 mm. The records of a total of 179 patients operated on for vestibular schwannoma (VS) removal via the RS-TM approach from January 1990 to June 1999 were also evaluated. Their ages ranged from 18 to 88 years (average 54 years). The tumor sizes ranged from 4 to 50 mm. Five patients had a solitary VS in the only hearing ear. INTERVENTION: The classic RS-TM approach was used in all patients. After tumor excision, for ABI implantation, the landmarks (seventh, eighth, and ninth cranial nerves, choroid plexus) for the foramen of Luschka were carefully identified. The choroid plexus was then partially removed, and the tela choroidea was divided and bent back. The floor of the lateral recess of the fourth ventricle and the convolution of the dorsal cochlear nucleus became visible. The electrode array was then inserted into the lateral recess and correctly positioned with the aid of electrically evoked auditory brainstem responses (EABRs). MAIN OUTCOME MEASURES: Intraoperative EABR and postoperative speech perception evaluation. RESULTS: Auditory sensations were induced in all patients with various numbers of electrodes. Different pitch sensations could be identified with different electrode stimulation. CONCLUSIONS: In the authors' experience, the RS-TM approach is the route of choice for patients who are candidates for ABI when there is a chance of hearing preservation during surgery. If auditory function is lost during surgery, anatomical preservation of the cochlear nerve may allow hearing restoration with a cochlear implant. Direct intraoperative recording of cochlear nerve action potentials (CNAPs) and round window electrical stimulation are mandatory for these purposes. In addition, decompression of the intrameatal portion of the vestibular schwannoma and planned partial tumor resection with hearing preservation are also possible with the RS-TM approach.
Acoustic Stimulation↗
Iatrogenic impairment of hearing during surgery for acoustic neuroma.
Isolated or combined labyrinthine, neural, and vascular damage account for failure to preserve hearing during removal of acoustic neuromas. However, the specific mechanisms of auditory impairment remain unclear unless surgical maneuvers can be related to peri- and postoperative hearing on the basis of intraoperative monitoring of auditory function.Among the different auditory monitoring techniques, recording of cochlear nerve action potentials (CNAPs) from the intracranial portion of the nerve has proven particularly useful for identifying the mechanisms of iatrogenic auditory injury.The present investigation analyzes intra- and postoperative auditory impairment in relation to surgical steps in a group of 38 subjects with acoustic neuroma (size ranging from 5 to 24 mm) undergoing removal via a retrosigmoid approach.Coagulation close to the cochlear nerve, drilling of the internal auditory canal, and removal of the intrameatal portion of the acoustic neuroma have prove to be the most critical surgical steps in hearing preservation.Changes were correlated with intra- and extrameatal tumor size, the relationship between the internal auditory canal and vestibule, and internal auditory canal enlargement, anatomic involvement of the cochlear nerve, preoperative auditory level, and ABR and ENG test findings.Changes in CNAP morphology and latency are detailed, and mechanisms of injury are analyzed and discussed as a function of these variables.
Journal Article↗