Three-channel Lissajous trajectories of auditory brainstem-evoked potentials in patients with neurological lesions affecting the brainstem: preliminary impressions.

Three-channel Lissajous trajectories (3CLT), as well as vertex-mastoid records of auditory brainstem-evoked potentials (ABEP) were obtained from 12 patients with neurological lesions localized to the auditory nerve, the medulla, the pons, the pons and midbrain and the midbrain. Patients selected had well-localized lesions at the levels of the presumed generators of ABEP (10 patients), as well as below (1 patient) and above (1 patient) those levels. The 3CLT measures used were trajectory amplitude, peak latency and amplitude, planar segment number, apex latency, duration, orientation in voltage space, as well as size and shape. Latencies and amplitudes of vertex-positive peaks I-V, as well as interpeak latency differences, were determined. Vertex-mastoid ABEP and 3CLT were compared in terms of their sensitivity to the existence of a lesion, the accuracy of lesion localization as well as their specificity to the lesion. 3CLT had an advantage in all three comparisons, with the most prominent advantage in specificity, which was over twice as high as that of single-channel ABEP. The results of this preliminary study indicate that 3CLT affords a sensitive analysis of ABEP, which is superior to single-channel analysis in sensitivity, accuracy and specificity. These results also indicate that the 'contralateral effect' of peak V latency prolongation in cerebellopontine angle tumors may be related to anatomical changes of its generators' orientation, rather than slowed conduction along the upper brainstem.