Cochlear implant and inflammation reaction: Safety study of a new steroid-eluting electrode.

Dexamethasone is a common anti-inflammatory agent added to cochlear implants to reduce hearing loss due to electrode insertion trauma. We evaluated the safety of eluting silicone rods containing 10% dexamethasone in a Guinea pig model. Animals were implanted with a dexamethasone eluting silicone electrode (DER) or with a non-eluting electrode (NER). The control group only underwent a cochleostomy (CS). Prior to implantation and during the two weeks following implantation, the hearing status of the animals was assessed by means of Compound Action Potentials (CAPs) with an electrode placed near the round window. Two weeks after implantation, the mean click threshold shifts were 1 dB ± 10 dB in the DER group, 10 dB ± 10 dB in the NER group and -4 dB ± 10 dB in the control group. After two weeks the bullae of each animal were extracted to verify the presence of macrophages, the percent of tissue growth in the scala tympani and the tissue sealing around cochleostomy. Silicone electrodes samples were also explanted and examined for bacterial infection. Neither bacterial infection nor enhanced number of macrophages were observed. A limited, but not significant, tissue growth was found in the scala tympani between the experimental and the control group. The data suggest that, in the Guinea pig model, the use of DER is apparently safe as an anti-inflammatory slow-release additive to the cochlear implant.

Vibrant Soundbridge for hearing restoration after chronic ear surgery.

INTRODUCTION: Middle ear surgery is primarily concerned with resolving the discharging pathology, in the case of chronic otitis media (COM), or with complete eradication, in case of cholesteatoma. Either of these procedures may require repeated surgeries, often resulting in severe mixed hearing impairment. A middle ear implant may be indicated in these cases instead of a hearing aid because the anatomical conditions in such cases often impede an adequate acoustic coupling. The objective of this study was to evaluate MED-EL Vibrant Soundbridge (VSB) implantation in patients with severe conductive and mixed hearing loss occurring after middle ear surgery for cholesteatoma or chronic otitis media (COM). MATERIALS AND METHODS: Over a 2-years period, the VSB system was implanted in 40 patients between 35 and 81 year old (mean: 59.5). Surgery was performed with comparable technique in 3 regional hospitals in Italy: Rovereto (n=16), Meran (n=12) and Tortona (n=12). The 40 candidates for implantation had a history of 1-5 previous surgeries. Of those, 20 patients suffered from COM and 20 from, cholesteatomas. The floating mass transducer (FMT) of the VSB was placed and stabilized on the round window niche in 32 cases; alternative positioning was necessary in 8 cases. Bone conduction (BC) was tested 1 day post-operatively. At 1 month post-surgery and between 6-9 months, open-field warble tones threshold in VSB-off and VSB-on conditions and open-field speech audiometry for words in quiet were conducted. RESULTS: Results of BC audiometry one day post-operatively showed no significant changes in hearing. Unaided mean pure tone average (PTA4) was 82.38 dB SPL with a mean speech recognition threshold (SRT) of 94.28 dB SPL. Results obtained after a minimum of three months post-operatively were evaluated in terms of aided thresholds and functional gain. At VSB activation, the mean PTA4 was 50.63 dB SPL with a mean SRT of 61.68 dB. After 6-9 months, the group had a mean PTA4 of 47.89 dB SPL and a mean SRT of 53.33 dB SPL. CONCLUSIONS: Implantation of the VSB with its direct driver of the inner ear fluids appears promising for auditory rehabilitation of severe mixed hearing loss associated with sequelae of cholesteatoma surgery. Patients' results improved over time, allowing us to assume a positive effect of consolidation of the coupling related to fibrosis. Results reported here refer to 6-9 months of observation and do not provide evidence of long term stability.

Role of CT and MRI in the preoperative evaluation of auditory brainstem implantation in patients with congenital inner ear pathology.

PURPOSE: The purpose of this study was to evaluate the reliability of computed tomography (CT) and magnetic resonance imaging (MRI) in characterising cochlear nerve anomalies in auditory brainstem implant candidates with congenital hearing loss. MATERIALS AND METHODS: Seventeen patients affected by congenital sensorineural hearing loss were examined by CT and MRI. Inner ear malformations eligible for auditory brainstem implants were classified according to the Casselman classification. All patients subsequently received auditory brainstem implants. RESULTS: Suspected congenital anomalies were confirmed by CT and MRI in all 17 patients. There were 5/17 bilateral cochlear nerve aplasias and 12/17 cochleovestibular anomalies. Of these, 5/12 patients had a common cochleovestibular cavity, 2/12 had bilateral cochlear aplasia and cochlear nerve agenesis, 1/12 had type I incomplete partition, 2/12 had type II incomplete partition and 2/12 had cochlear hypoplasia. CONCLUSIONS: Preoperative CT and MRI assessment of patients with sensorineural hearing loss is reliable. MRI provided additional information, identifying the possible absence of cochlear nerve and excluding other central nervous system (CNS) diseases.

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.

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.

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.

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.

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.

Improved auditory performance of cochlear implant patients using the middle fossa approach.

The preliminary results of insertion of a cochlear implant via the middle fossa in nine patients with profound bilateral hearing loss are described. Aetiologies included a bilateral radical mastoidectomy cavity, adhesive otitis media, autoimmune inner ear disease, previous cranial trauma, genetic pre-lingual deafness, and otosclerosis. A classic middle fossa approach was adopted. A small cochleostomy measuring 1.5 mm in diameter was performed on the most superficial part of the basal turn. A Nucleus 24M cochlear implant system (Cochlear Corporation) was inserted in four patients, a Lauraflex implant (Philips Hearing Implants) was used in three patients and a Combi 40+ (Med-el) with a double electrode array in two. Single electrode arrays were inserted from the cochleostomy to the cochlear apex and occupied a portion of the basal turn, as well as the middle and apical turns. Double electrode arrays were inserted, one towards the apex and one into the basal turn of the cochlea towards the round window. The receiver stimulator was positioned in a bone well previously drilled in the temporal squama and the electrode carrier was inserted in the fenestrated cochlea. The activity of the inserted electrodes was tested by means of telemetry and intraoperative recording of electrically evoked auditory brainstem responses (EABR). Speech recognition tests, performed over a period of time ranging from one to six months after cochlear implant activation, yielded better results in these patients compared with those obtained in postlingually deaf patients operated on via the traditional transmastoid route. Cochlear implant insertion via the middle fossa approach is a technique which is suitable for the implantation of patients with bilateral radical mastoidectomy cavities, chronic middle ear disease, middle ear malformations, or with partial obliteration of the cochlea in the basal turn. However, the main advantage of inserting the implant through the middle fossa cochleostomy consists in the possibility of stimulating, with the single array, areas of the cochlea, i.e. part of the basal, middle and apical turns, where a greater survival rate of spiral ganglion cells is known to occur. In addition, with the double array total occupation of the cochlea is possible, providing the possibility of replicating the tonotopic organization of the cochlea. This new approach has led to major improvements in speech recognition in all patients compared with patients operated on via the transmastoid approach and, given the present state of the art, may be the elective approach for optimal implantation outcomes.