内耳遅延造影 MRI にて内リンパ水腫を認めた迷路内神経鞘腫例

We report a case of intralabyrinthine schwannoma with endolymphatic hydrops. A 60-year-old man presented with sudden onset of right-sided hearing loss, aural fullness, tinnitus, and dizziness. His pure-tone audiograms showed mild-to-moderate sensorineural hearing loss, particularly at low frequencies, which, however, spread across all frequencies after a few days. The distortion-product otoacoustic emission (DPOAE) level of the right ear had decreased below the noise level. Equilibrium function tests showed slight leftward spontaneous nystagmus and semicircular canal paralysis in the right ear. The hearing level then gradually recovered once and then began to fluctuate. Gadolinium-enhanced T 1-weighted imaging revealed an intralabyrinthine schwannoma, corresponding to “Intravestibular type” of the Modified Kennedy classification system. Four-hour delayed gadolinium-enhanced 3 D-FLAIR MR images showed strong enhancement in the right cochlea and lateral semicircular canal, and HYDROPS images revealed endolymphatic hydrops at the apical and middle turns in the cochlea. Follow-up MRI showed persistent strong enhancement in the right cochlea and revealed that the cochlear endolymphatic hydrops had developed to the basal rotation too over a one-year period. Alterations in the blood-labyrinth barrier permeability and endolymphatic hydrops due to obstruction of the endolymphatic cavity were assumed as being involved in the pathogenesis of the cochlear symptoms in this case.