The majority of the evidence reviewed was poorly reported and there is therefore an inherent risk of bias. Given the recent improvement in resolution and reduction in cost of MR imaging, ABR can no longer be considered appropriate as the primary test used to screen for acoustic neuroma. T2W or T2*W sequences enable accurate evaluation of the VIIIth and VIIth cranial nerves within the cerebellopontine angle and internal auditory canal as well as evaluation of the cochlea and labyrinth, and inclusion of GdT1W sequences is unlikely to contribute information that would alter patient management in the screening population. The quality of the imaging chain and experience of the reporting radiologist are key factors determining the efficacy of a non-contrast screening strategy. Based on a cost-effectiveness model developed to reflect UK practice it was concluded that a diagnostic algorithm that deploys non-contrast MR imaging as an initial imaging screen in the investigation of acoustic neuroma is less costly than and likely to be as effective as available contrast MR imaging.
With increasing use of imaging in the investigation of cerebello-pontine angle (CPA) tumours, the role of audio-vestibular and electrophysiological testing has changed. Field performance data on the efficiencies of these tests to screen for CPA tumours are lacking, but must be known to choose an appropriate testing strategy. A prospective observational study of 237 patients attending a neuro-otology clinic for audio-vestibular investigation was carried out. The aim was to provide field performance data on which to base an effective protocol to screen for CPA tumours. All patients presenting at the ENT department and meeting any of the following criteria were referred to the neuro-otology clinic and included in the study: (1) asymmetrical sensorineural hearing loss, (2) unexplained asymmetrical tinnitus with normal bearing thresholds, (3) unilateral bearing difficulties with normal hearing thresholds and (4) other neurological indications. In addition to audio-vestibular and auditory brainstem response (ABR) investigation, every patient underwent computed tomography (CT), with magnetic resonance imaging (MRI) in cases having marginal results on CT, to exclude or confirm the presence of a tumour. Pass or fail on each test was based on a priori criteria from other studies. Eighteen patients were found to have CPA tumours. ABR testing was the only effective procedure for screening, but had some limitations. A contingent protocol using ABR in all cases except those with asymmetrical tinnitus and normal bearing thresholds, those with severe hearing loss, and those with neurological signs, was retrospectively defined: the exceptions would go straight to CT. This protocol would have missed two of the 18 tumour patients. CT scanning alone would have missed one small intra-canalicular tumour, which was picked up on MRI triggered by abnormal ABR. Based on the results from the present study we conclude there is no effective screening protocol for detecting CPA tumours, as MRI scanning with gadolinium enhancement will identify virtually all tumours. Where MRI is available but waiting lists are long, the described strategy using ABR to select priority referrals for MRI scanning is recommended.
The symptom of poor speech discrimination in the presence of background noise is a well-recognized feature of elevated hearing thresholds due to cochlear damage. Similar symptoms occasionally occur in patients with no detectable audiological abnormality. In a study to evaluate the frequency selectivity of such patients consistent abnormalities were found using an electrophysiological technique based on extratympanic electrocochleography. These findings indicated that frequency specific responsiveness of the cochlea may be affected before conventional behavioural tests reveal abnormalities. This syndrome has been described as selective dysacusis.
Cochlear implantation of young children (<5 years of age) places additional demands on the implant team when compared to older children and adults. For these young children, it is essential to have integrity testing (IT) available to objectively assess the function of the internal device. Unfortunately, very few publications are available which document normal working ranges for IT. Thus the aim of the present study was to establish intra- and post-operative normal ranges for the averaged electrode voltage (AEV) which can be used in the clinical environment to assist in child management. As part of the routine protocol in Nottingham, IT was performed intra-operatively and 2 or 5 years post-operatively in common ground (CG) and pseudo-monopolar 1 (MP1) modes of stimulation on 30 children. All the children were implanted with the Nucleus mini 22 device. Normal ranges were calculated (mean +/- 1 standard deviation (SD)) for both intra- and post-operative measurements. In addition, the post-operative percentage changes in AEV amplitude were calculated for the 2-year and 5-year data groups. Data were excluded from calculations if an electrode was known or suspected to be faulty by visual examination of the AEV profile by an experienced observer. The results demonstrated that the profile of the AEV across the electrode array was preserved between intra- and post-operative recordings, although the amplitude of all AEVs decreased post-operatively. The percentage decrease (mean +/- SD) in (i) CG after 2 years was 69 (+/-16%), (ii) in CG after 5 years was 77 (+/-15%) and (iii) in MPI after 2 years was 35 (+/-1%). IT is a valuable objective tool to assess device function, in particular for young children. Normal AEV ranges are presented which can be used in the clinical environment to aid interpretation of IT performed intra- and post-operatively for CG and MP1 modes. Test data validate the implementation of normal ranges. Electrodes whose values of AEV amplitude fall outside the range should be investigated further.
The Nottingham Paediatric Cochlear Implant Programme (NPCIP) specializes in the cochlear implantation of children under the age of 5 years. The initial stage in the pre-implant evaluation process is audiological assessment. In complex paediatric cases, behavioural audiological assessment may be difficult. In such cases, an objective measure to verify the aided hearing threshold is desirable. This study compares unaided and aided hearing thresholds, by both objective and behavioural techniques, in 20 children (aged <1-10 years). Objective data were collected from auditory brainstem responses (ABR) and behavioural thresholds were measured by use of developmental age-appropriate tests. When comparing the unaided ABR click threshold to the behavioural threshold (obtained from the average of 1-4 kHz warble tones) the ABR threshold was, on average, 9 dB lower (more sensitive). Using the same comparison for aided responses a difference of <5 dB was observed. Unaided ABR thresholds resulted in 35% of subjects responding to the click stimulation (when using a maximum stimulation level of 105 dB nHL), whereas introducing aided ABR measurement elicited positive results in 75% of subjects. The effect of the hearing aid on the stimulus was measured by use of a 2 cc coupler which was connected to a precision sound level meter, whose AC output was recorded onto digital audiotape. Analysis of the resultant output spectra in the frequency domain highlighted signal non-linearity and distortion when using high-intensity stimuli with moderate to high aid gains. In conclusion, aided ABR thresholds are valuable in the management of young children. However, when performing either ABR or behavioural aided hearing threshold measurements it is essential to be aware of the limitations of the hearing aid and the stimulus.
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