Comparative evaluation of ABR abnormalities in patients with and without neurinoma of VIII cranial nerve.

Although the diagnostic reliability of auditory brainstem responses (ABR) in acoustic neuromas has been revised due to its poor sensitivity (demonstrated above all in smaller tumours), and its limited specificity, this method is still used as the initial otoneurological approach. To contribute to the clinical use of this method, in particular with the aim of reducing the number of false positives, a retrospective study was carried out in two groups of patients affected by unilateral sensorineural hearing loss with auditory brainstem response abnormalities: in the first group (50 cases: true positives) hearing loss was the expression of an acoustic neuroma shown by magnetic resonance imaging, in the second group (130: false positives) magnetic resonance imaging was negative. In both groups, auditory brainstem response recordings showed abnormalities suggesting retro-cochlear disorders such as: (1) complete absence of response not justified by the extent of the hearing loss, (2) presence of only wave I, (3) increase in wave V absolute latency with normal I-V interpeak latency, (4) increase in wave V absolute latency, the sole component, 5) increase in wave V absolute latency and I-V interpeak latency. A comparison between the two groups made it possible to show that the finding of "major" auditory brainstem response alterations (complete absence of response not justified by the extent of the hearing loss or presence of only wave I) is correlated with a high probability of the presence of a neuroma, while other abnormalities (wave V latency and I-V interpeak latency increase) have no particular predictive value since percentages are almost identical in the two groups. Wave V latency increase with normal I-V interpeak latency was observed in only one case of acoustic neuroma and this clinical finding is not easy to interpret. It would not appear possible, based on current knowledge, to further improve the reliability of this test, and, therefore, its use in oto-neurological diagnostics remains limited.