Abstract
The auditory brainstem responses (ABRs) obtained in 47 subjects with asymmetric hearing loss (12 with surgically confirmed cerebello-pontine angle tumours, 35 without otoneurologic and/or neuroradiologic evidence of tumour) were evaluated by means of an index named ΔV. The calculation of this index was based upon the patient's wave V absolute latency obtained at a fixed intensity of 90 dB HL and the value of latency predictable by means of the normative data. The index clearly separates retrocochlear from cochlear sites of lesion. Moreover ΔV values obtained in defined cochlear lesions show a linear relation with the patient's pure tone hearing loss at 2 and 4 kHz; this behaviour is probably due to a reduction of the auditory dynamic range in the recruiting ears. ΔV appears to have clinical usefulness because of two main points: first it is based upon an evaluation of the monaurally evoked ABR; second, it improves the diagnostic specificity of the responses. The rate of false positive results can be further reduced by combining ΔV and IT5 values.