MRI measurement of the canine auditory pathways and relationship with brainstem auditory evoked responses.

The objective of this study was to determine direct measurements of auditory pathways by magnetic resonance imaging (MRI) during the growth period of healthy Beagles, and to discover how canine brainstem auditory evoked response (BAER) latencies vary in relation to these MRI measurements. Eighty healthy Beagles were tested at eight, 16 and 52 weeks of age (stages 1, 2, 3, respectively) with BAER and brain MRI. The BAER interpeak latency (IPL) II-V and brain MRI neural generators of BAER waves II and V were identified. A linear distance was calculated in millimeters in order to determine the approximate length of auditory pathways. Sensory nerve conduction velocity (SNCV) of the auditory pathway between peak II and peak V was calculated for each group. A significant difference was observed between brain MRI distances among the three stages. Mean BAER IPL II-V were not significantly different between the three stages. The progressive growth of the skull and brain witnessed by the progressive increased distance of the MRI auditory pathways between peak II and peak V was not associated with a progressive maturation of the BAER IPL II-V. The SNCV of the auditory pathway between peak II and peak V was 6.14 m/sec for group 1; 6.76 m/sec for group 2; and 7.32 m/sec for group 3.