Latency of the auditory brainstem response (ABR) and head size. Evidence of the relationship by means of radiographic data.

The role of head size to determine the inter-subject variability of the auditory brainstem response (ABR) was investigated in 32 normally hearing adults (19 females, 13 males, aged 18 to 52). The ABRs were evaluated in respect to the absolute latency of waves I, III and V and the interpeak latencies I-III, III-V and I-V. Plain films of the skull (3 views) were also taken of each subject and several measures were calculated in order to obtain an evaluation of the dimensions of both the most rostral parts of the skull and of the posterior fossa. The radiographic data as well as the ABR parameters showed significantly shorter values in females than in males. There was a strong positive correlation between the two variables when a linear regression procedure was applyed. The highest value of the correlation coefficient (r = 0.8) was found in the relationship between the wave V latency and the posterior fossa measures. High r values and similar factors in the regression equation were also found after considering the subjects separately according to sex. These results show that the ABR latencies linearly increase together with the skull size as it appears in the X-rays, regardless of the subject's sex. We can consequently deduce that the length of the neural pathway is the main factor of inter-sex variability of the response.