Objective: To investigate a narrow internal auditory canal (IAC) syndrome u
sing functional magnetic resonance imaging (fMRI) of the auditory cortex.
Study Design: The study design was a case report. The follow-up period last
ed 18 months.
Setting: The study was carried out in the audiology clinic of an ear, nose,
and throat department and in the department of pediatric neuroradiology at
a university hospital.
Main Outcome Measures: Age-appropriate observational audiometry, objective
audiovestibular tests, computed tomography (CT), magnetic resonance imaging
(MRI), and (fMRI) of the auditory cortex were performed to analyze in deta
il the profound deafness of a young child.
Results: Audiovestibular examination demonstrated both measurable hearing a
nd normal vestibulo-ocular reflex, and CT showed narrow IACs combined with
normal labyrinths. Axial MR images completed by sagittal sections perpendic
ular to the IAC delineated a single nerve that was initially supposed to be
the facial nerve. No cochleovestibular nerve was identified. However, fMRI
performed with the patient under general anesthesia demonstrated activatio
n of the primary auditory cortex during 1-kHz monaural stimulation on the l
Conclusions: The absence of cochleovestibular nerve on MR studies cannot ex
clude connections between the inner ear and the central auditory pathways.
This might be caused by a lack of spatial resolution of anatomical MR studi
es. The single nerve delineated within the IAC might also carry both facial
and cochleovestibular fibers. Functional MRI can assess the cortical respo
nse to acoustic stimuli when aplasia of the cochleovestibular nerve is susp
ected. This case study illustrates a novel and atypical presentation of coc
hlear nerve dysplasia.