Radiographic analysis of cochlear nerve vascular compression.

OBJECTIVES We analyzed whether radiographically demonstrated anterior inferior cerebellar artery (AICA) vascular compression of the cochleovestibular nerve in asymmetric hearing loss could be correlated to either the symptomatic ear or to cochlear nerve diameter. METHODS We undertook a retrospective case-control study in which patients were enrolled into a database if audiometry demonstrated asymmetry of 20 dB at one frequency, asymmetry of 10 dB at two frequencies, or a difference of 20% on word recognition scores. If AICA vascular contact was demonstrated on subsequent magnetic resonance imaging of the cerebellopontine angle, patients were included in the study. Patients with vestibular schwannoma or Meniere's disease were excluded. The AICA contact was graded by a blinded neuroradiologist according to criteria proposed by McDermott et al. The cross-sectional area of the cochlear nerve was measured. RESULTS Symptomatic ears could be correlated to a decreased cochlear nerve diameter, but not to the degree of AICA penetration into the internal auditory canal. CONCLUSIONS AICA vascular compression of the cochleovestibular nerve does not appear to correlate to hearing loss or to cochlear nerve diameter. The finding of decreased cochlear nerve diameter in symptomatic ears implies an alternative mechanism for asymmetric hearing loss.