Partitioned Internal Auditory Canal: Association With Cochlear Aperture Anomalies.

Abstract

To investigate the association between partitioned internal auditory canal (IAC) and other inner ear abnormalities. The temporal bone computed tomography (CT) and magnetic resonance imaging (MRI) findings of ears with partitioned IAC were retrospectively analyzed. The IAC was considered narrow if its mid-portion diameter < 2 mm. Cochlear aperture (CA) was classified as normal (diameter more than 1.5 mm), stenotic (diameter < 1.5 mm), or atretic. The MRI images examined the cochlear nerve (CN). The CN's diameter was compared with the ipsilateral facial nerve to determine if it was normal, hypoplastic, or aplastic. Partitioned IAC was observed in 1.1% of ears with normal CA, 14.9% of ears with stenotic CA, and 20.9% of ears with atretic CA. Forty-eight right and 37 left ears with partitioned IAC were examined. The most common CA anomaly accompanying partitioned IAC was CA stenosis, while more than half of the cochleae were of normal size. IAC was mostly narrow in ears with partitioned IAC. When the CN was examined, partitioned IAC was almost always accompanied by CN aplasia (more frequently) or hypoplasia. This study demonstrates that CN deficiency, associated with CA abnormalities, may cause the aberrant location of the meatal segment of the facial nerve in a separate bony canal. Partitioned IAC is an inner ear malformation characterized by CN deficiency.