Abstract
Objective. To explore possible corelationship between the cochlear nerve deficiency (CND) and unilateral auditory neuropathy (AN). Methods. From a database of 85 patients with unilateral profound sensorineural hearing loss, eight who presented with evoked otoacoustic emissions (EOAEs) or cochlear microphonic (CM) in the affected ear were diagnosed with unilateral AN. Audiological and radiological records in eight patients with unilateral AN were retrospectively reviewed. Results. Eight cases were diagnosed as having unilateral AN caused by CND. Seven had type “A” tympanogram with normal EOAE in both ears. The other patient had unilateral type “B” tympanogram and absent OAE but CM recorded, consistent with middle ear effusion in the affected ear. For all the ears involved in the study, auditory brainstem responses (ABRs) were either absent or responded to the maximum output and the neural responses from the cochlea were not revealed when viewed by means of the oblique sagittal MRI on the internal auditory canal. Conclusion. Cochlear nerve deficiency can be seen by electrophysiological evidence and may be a significant cause of unilateral AN. Inclined sagittal MRI of the internal auditory canal is recommended for the diagnosis of this disorder.
Highlights
Auditory neuropathy (AN) is a clinical syndrome characterized by the absence of, or the grossly abnormal, auditory brain stem response (ABR) in the presence of normal outer hair cell function as revealed by otoacoustic emission (OAE) and/or cochlear microphonic (CM) [1]
One person had type “B” tympanogram with ipsilateral and contralateralacoustic reflexes were absent in the affected ear stimulation
evoked otoacoustic emissions (EOAEs) and CM were present in seven patients
Summary
Auditory neuropathy (AN) is a clinical syndrome characterized by the absence of, or the grossly abnormal, auditory brain stem response (ABR) in the presence of normal outer hair cell function as revealed by otoacoustic emission (OAE) and/or cochlear microphonic (CM) [1]. Most ANs show bilateral presentation accompanied by typical audiological features, but recent studies suggest that some AN cases involve only one ear [2,3,4]. This kind of patients could be missing because of the present EOAE during the newborn hearing screening. Eight unilateral AN cases were found in our hospital, and all of them were diagnosed as cochlear nerve deficiency (CND) on MRI. This findings support the routine use of MRI on unilateral AN
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