Yu Chuen Tam

MRI without magnet removal in neurofibromatosis type 2 patients with cochlear and auditory brainstem implants.

Objective To assess the impact on image quality of MRI without magnet removal in cochlear implant (CI) and auditory brainstem implant (ABI) users with neurofibromatosis type 2 (NF2). Study Design Prospective cohort. Setting Tertiary center for cochlear and auditory brainstem implantation. Patients Thirteen patients (10 ABI, 3CI) with NF2 underwent a total of 76 MRI scans. Interventions MRI without magnet removal. Main Outcome measure Ability to visualize the ipsilateral and contralateral cerebellopontine angles (CPAs) and internal auditory meati (IAM) with head MRI. Results Of the 76 scans, 40 were of the head, 28 of the spine and 8 of other regions. Scanning was performed with a tight head bandage and plastic card. There were no cases of altered implant function or demagnetization of the device magnet. A grading system was used to assess the view of the ipsilateral IAM-CPA. In 85% of head scans, the view was unimpaired (Grade 0). In 13%, there was distortion (Grade 1). In 2% (1 case), the view was entirely obscured by artifact (Grade 2). Views of the contralateral CPA and IAM were unimpaired in all cases. The best 3 sequences for the depiction of the ipsilateral IAM-CPA (percent graded as 0) were as follows: axial 3D inversion recovery prepared fast spoiled gradient echo (100%), 2 mm coronal T1W of the IAM-CPA (88.9%), and 2 mm axial T1W of the IAM-CPA (76.9%). Conclusion MRI scanning without magnet removal is safe and well tolerated in NF2 patients with auditory implants. With appropriate MRI sequences, the image quality is not significantly impaired.

Surgical management of vestibular schwannomas and hearing rehabilitation in neurofibromatosis type 2.

Objectives To report our approach to the surgical management of vestibular schwannomas (VSs) and hearing rehabilitation in neurofibromatosis Type 2 (NF2). Design Retrospective cohort study. Setting Tertiary referral NF2 unit. Patients Between 1981 and 2011, seventy-five patients were managed in our NF2 unit, of which, 58 patients are under current review. Main Outcome Measures Patients who underwent VS excision were evaluated for tumor size, surgical approach, and outcomes of hearing and facial nerve function. All current patients were evaluated for NF2 mutation, hearing, and auditory implantation outcomes. Results Forty-four patients underwent resection of 50 VS in our unit, of which, 14% had facial neuroma excision and reinnervation during the same operation. At 12 months after surgery, facial nerve outcomes were House-Brackmann (HB) 1 in 33%, HB2 in 21%, and HB3 in 30%. Total VS resection was achieved in 78% of patients using a translabyrinthine approach. Seventy-two percent of the current patients have American Association of Otolaryngology–Head and Neck Surgery class A to C hearing (maximum speech discrimination score over 50%) in the better hearing ear, and a further 14% are full-time users of cochlear implants or auditory brainstem implants. The remaining patients have been assessed for auditory implantation. Conclusion By following a policy of treating VS in NF2 patients where tumor growth is observed, complete tumor resection can be achieved through a translabyrinthine approach while achieving comparable facial nerve outcomes to published series. We advocate proactive hearing rehabilitation in all patients with timely assessment for auditory implantation to maintain quality of life.

Magnetic Resonance Imaging in Patients with Cochlear Implants and Auditory Brain Stem Implants

Abstract Despite extensive testing, many radiology departments are reluctant to perform MRI scans on patients fitted with cochlear or auditory brain stem implants. In house testing was performed on the three models of cochlear implants supported by our centre, to verify the manufacturers MRI compatibility data. We present the results from our in house testing and 25 patients with implants that have undergone MR imaging.

Pitch Discrimination: An Independent Factor in Cochlear Implant Performance Outcomes.

Objective: To assess differences in pitch-ranking ability across a range of speech understanding performance levels and as a function of electrode position. Study Design: An observational study of a cross-section of cochlear implantees. Setting: Tertiary referral center for cochlear implantation. Patients: A total of 22 patients were recruited. All three manufacturers’ devices were included (MED-EL, Innsbruck, Austria, n = 10; Advanced Bionics, California, USA, n = 8; and Cochlear, Sydney, Australia, n = 4) and all patients were long-term users (more than 18 months). Twelve of these were poor performers (scores on BKB sentence lists <60%) and 10 were excellent performers (BKB >90%). Intervention: After measurement of threshold and comfort levels, and loudness balancing across the array, all patients underwent thorough pitch-ranking assessments at 80% of comfort levels. Main Outcome Measure: Ability to discriminate pitch across the electrode array, measured by consistency in discrimination of adjacent pairs of electrodes, as well as an assessment of the pitch order across the array using the midpoint comparison task. Results: Within the poor performing group there was wide variability in ability to pitch rank, from no errors, to a complete inability to reliably and consistently differentiate pitch change across the electrode array. Good performers were overall significantly more accurate at pitch ranking (p = 0.026). Consistent pitch ranking was found to be a significant independent predictor of BKB score, even after adjusting for age. Users of the MED-EL implant experienced significantly more pitch confusions at the apex than at more basal parts of the electrode array. Conclusions: Many cochlear implant users struggle to discriminate pitch effectively. Accurate pitch ranking appears to be an independent predictor of overall outcome. Future work will concentrate on manipulating maps based upon pitch discrimination findings in an attempt to improve speech understanding.

Effect of chronic stimulation and stimulus level on temporal processing by cochlear implant listeners

A series of experiments investigated potential changes in temporal processing during the months following activation of a cochlear implant (CI) and as a function of stimulus level. Experiment 1 tested patients on the day of implant activation and two and six months later. All stimuli were presented using direct stimulation of a single apical electrode. The dependent variables were rate discrimination ratios (RDRs) for pulse trains with rates centred on 120 pulses per second (pps), obtained using an adaptive procedure, and a measure of the upper limit of temporal pitch, obtained using a pitch-ranking procedure. All stimuli were presented at their most comfortable level (MCL). RDRs decreased from 1.23 to 1.16 and the upper limit increased from 357 to 485 pps from 0 to 2 months post-activation, with no overall change from 2 to 6 months. Because MCLs and hence the testing level increased across sessions, two further experiments investigated whether the performance changes observed across sessions could be due to level differences. Experiment 2 re-tested a subset of subjects at 9 months postactivation, using current levels similar to those used at 0 months. Although the stimuli sounded softer, some subjects showed lower RDRs and/or higher upper limits at this re-test. Experiment 3 measured RDRs and the upper limit for a separate group of subjects at levels equal to 60%, 80%, and 100% of the dynamic range. RDRs decreased with increasing level. The upper limit increased with increasing level for most subjects, with two notable exceptions. Implications of the results for temporal plasticity are discussed, along with possible influences of the effects of level and of across-session learning.