Duplication Anomalies of the Internal Auditory Canal: Varied Spectrum

Internal auditory canal duplication with facial and cochlear nerve dysfunction: A case report

Internal auditory canal duplication is a rare anomaly of the temporal bone. The condition is diagnosed on performing High-Resolution Computed Tomography of the temporal bone and magnetic resonance imaging for sensorineural hearing loss. A bony septum divides the internal auditory canal into dual compartments. Duplication may be either unilateral or bilateral and vestibulocochlear nerve may be aplastic or hypoplastic. Rarely, patient may present with facial nerve palsy. A 26-year-old female presented with right grade IV lower motor neuron facial nerve palsy for 12 years and right-sided hearing loss for 9 years. Pure tone audiogram revealed 45 dB of moderate degree sensorineural hearing loss on the right ear. On High-Resolution Computed Tomography of the temporal bone, an incomplete bony septum was visualized in the right internal auditory canal, dividing it into two compartments. Internal auditory canal on the left side was normal. Other inner and middle ear structures were normal. On magnetic resonance imaging, both the vestibulocochlear and facial nerves were well visualized with normal calibers.

De novo sensorineural hearing loss sequelae of narrow, duplicated internal auditory canal: Case series and literature review

INTRODUCTION

A narrow duplicated internal auditory canal (IAC) is an extremely rare anomaly, likely associated with congenital sensorineural hearing loss due to aplasia/hypoplasia of the vestibulocochlear nerve or the cochlear branch alone. We aimed to review our experience with IAC duplication, describe its clinical characteristics, and present a literature review.

CASE PRESENTATION

Our Otology database was searched for children who showed duplication of the IAC. Clinical characteristics of two children with bilateral duplication of the IAC are described. Data regarding clinical history, auditory assessment, magnetic resonance imaging (MRI), and computed tomography (CT) were collected and analyzed. The separated, accessory bony canals were demonstrated on high-resolution CT scans, and the nerves were demonstrated on MRI.

DISCUSSION

To date, a few cases of narrow duplicate IAC have been reported in the literature, Approximately 20% of patients with congenital SNHL are found to show inner-ear bony abnormalities on CT, but much uncertainty still exists about the mechanism underlying IAC stenosis.5 Imaging findings of the temporal bone in our case series demonstrated asymmetrical narrowing of both IACs, there is no clear evidence in the literature supporting the predominance of one side over the other. In our series, facial nerve function was intact bilaterally. As for our cases, both patients were enrolled in a single-sided deafness evaluation for a trial of options such as BAHA, CROS, cochlear implants, and other non-implantable hearing aids. Furthermore, addressing the important factors will optimize the outcomes including surgery at early age to optimize neural plasticity, with intense long-term therapy.

CONCLUSION

Congenital duplication of the IAC likely convoying sensorineural hearing loss due to aplasia/hypoplasia of the vestibulocochlear nerve. Early diagnosis and intervention are essential to optimize patient outcomes.