Duplicate Cochlea and Cranial Nerve

Introduction: Duplication anomalies of the internal auditory canal (IAC) are rare and usually accompanied by other inner ear malformations. To our knowledge, there are no previously described cases of duplication of the cochlea. In this case study, we report a patient incidentally found to have a second left cochlea and nerve on imaging.

Methodology: Retrospective case review.

Case Presentation: A 72-year-old woman presented for management of previously diagnosed right-sided Meniere’s disease. The patient reported a history of vertigo and fluctuating right-sided hearing loss and aural fullness. She additionally endorsed bilateral tinnitus, but was otherwise subjectively asymptomatic in her left ear. Otologic examination was unremarkable and both right and left facial nerve function was normal. Audiogram tracing of her right ear demonstrated moderate hearing loss from 250 to 4,000 Hz, sloping to moderately severe hearing loss from 6000–8000 Hz. While her left ear showed mild sensorineural hearing loss at 250–1500 Hz, recovering to normal hearing sensitivity from 2000–4000 Hz, then sloping to a moderate sensorineural hearing loss at 6000–8000 Hz. Video-nystagmography (VNG) showed abnormal saccade latencies bilaterally. Additionally, patient underwent MRI brain and internal auditory canal during her outpatient neurology work-up. On imaging, a second left rudimentary cochlea was identified inferior and posterior to the left internal auditory canal with its own, separate nerve connecting to the brainstem. Excluding this anomaly, imaging otherwise demonstrated radiographically normal inner ear structures bilaterally.

Discussion: Congenital malformations of the inner ear may include changes to the membranous labyrinth alone or with involvement of the bony labyrinth. Duplication anomalies of the inner ear have rarely been observed in the IAC. Duplicated IAC is thought to be a result of aplasia of hypoplasia of the vestibulocochlear nerve and in the few reported cases, duplicated IAC is usually accompanied by other inner ear malformations. To our knowledge, this is the first documented case of a second cochlea. Interestingly, our patient’s duplicative cochlea was not present with other inner malformations and her hearing was not impacted. This anomaly appears to be unique and likely explained by a process different than the developmental arrest underlying previously described malformations.

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Artikel online veröffentlicht:
05. Februar 2024