Detection of reduced diameter of nervus cochlearis in long term deaf patients quantified with semiautimatic 3 tesla MRI ZOOMIT sequence

Beside audiological testing routine preoperative evaluation includes MRI scan of the neurocranium. This allows the evaluation of the morphology of the nerves in the inner ear canal. Earlier studies have shown that the diameter of the cochlear nerve can be used as prognostic marker for the auditory performance after cochlear implantation. In this study we used 3 tesla MRI ZOOMIT sequence together with semiautomatic analysis to determine the maximal area of the nerves in the inner ear canal. We therefore retrospectively analyzed 100 3 tesla MRI scans with ZOOMIT Sequence using our semiautomatic tool to measure area of cochlear, vestibular and facial nerve in the inner ear canal and correlated this with patient history and audiology testing. We evaluated 5 groups of patient with a length of deafness of more than 20 years (normakusis, 11-40 dB hearing loss (hl), 41-70 dB hl, 71-100 dB hl and complete deafness) and calculated the quotient of cochlear and facial nerve area. There was a significant difference between patients with normakusis (1.29 ± 0.15 mm2) and patients with hearing loss of more than 41 dB (1.03 ±0.16, 0.99 ± 0.07 und 0.88 ± 0.1 mm2). However there was no significant difference in patients with moderate hearing loss (11-40 dB). Therefor we could show that in long term deaf patients, the diameter of the cochlear nerve is decreasing the more severe the hearing loss is. Also, the maximal area of the facial nerve was not different between all groups. This tool can therefore be used prior to cochlea implantation to assess nerve diameter and possibly determine patients with nerve degeneration that will possibly not profit from cochlear implantation or vice versa.