Aspects in diagnostics of central neural hearing disorders.
The central neural hearing disorders - in contrast to central cortical lesions - can be concretely defined audiometrically, and they can be localized realiably within the 2nd-4th neurons. For this purpose a definite test program is needed; especially indicative are the behavior of the acoustico-facial stapedius reflex and the results in dichotic discrimination and ERA. SISI and difference limen mostly point to a neural dysfunction, but - in distinct patterns of impairment - they may correspond to the picture of a peripheral hearing disorder as well. A fatigue of hearing apparently only appears if the myelin is damaged, at - perhaps additional - axonal lesions it shows up less clearly or not at all. The deficiency pattern of the stapedius reflex reflects up less clearly or not at all. The deficiency pattern of the stapedius reflex reflects the course of the reflex arc within the brain stem; accordingly, more central lesions of the auditory pathway do not affect the reflex. ERA mostly makes perceivable a lesion of synchronization, which only becomes noticeable at fast repetition rates with ultra short stimuli (1/4 ms), i.e., solely in the responses of the brain stem. The cortical responses, on the contrary, are not impaired more than the subjective threshold renders to be expected, they even show the same values of the pure tone audiogram. The dichotic discrimination is nearly always disturbed unilaterally, at processes of the brain stem homolaterally, at cortical foci predominantly leftside, perhaps because the left hemisphere dominates in speech discrimination. The otologist should know how to make use of the possibility of neuro-otologic diagnostics.
D000328:Adult; D000368:Aged; D001299:Audiometry; D001932:Brain Neoplasms / Q000601:surgery; D002530:Cerebellopontine Angle; D014695:Cerebral Ventriculography; D005072:Evoked Potentials, Auditory; D005154:Facial Nerve / Q000503:physiopathology; D006313:Hearing Loss, Central / Q000175:diagnosis*; D006319:Hearing Loss, Sensorineural / Q000175:diagnosis*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000150:complications; D012018:Reflex; D012022:Reflex, Acoustic; D013198:Stapedius; D014057:Tomography, X-Ray Computed