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Clinical Note |

Narrow Duplicated Internal Auditory Canal:  A Rare Inner Ear Malformation With Sensorineural Hearing Loss

Tatsuo Kono, MD; Shigeko Kuwashima, MD; Hiroaki Arakawa, MD; Erena Yamazaki, MD; Kazuhiro Kitajima, MD; Yasuo Ejima, MD; Tsutomu Ishikawa, MD; Teisuke Hashimoto, MD; Yasushi Kaji, MD
Arch Otolaryngol Head Neck Surg. 2009;135(10):1048-1051. doi:10.1001/archoto.2009.137.
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A narrow duplicated internal auditory canal (IAC) is a very rare congenital inner ear malformation, with only 5 cases (to our knowledge) reported in the literature.15 A 14-year-old girl with unilateral sensorineural hearing loss (SNHL) showed 2 narrow (<1 mm) bony canals in the inner ear portion of the left temporal bone on computed tomograms (CTs). The anterior canal continued to the bony canal of the facial nerve, and the posterior canal continued to the cochlea. Other than a lack of development of the canal for the cochlear nerve, the cochlea was normal. High-resolution magnetic resonance images (MRIs) revealed a single thin cranial nerve located in the anterior canal. However, a cranial nerve was not found in the posterior canal. Therefore, a diagnosis of a unilateral narrow duplicated IAC with a hypoplastic vestibulocochlear nerve and vestibular-semicircular canal malformation was made. Computed tomography plays an important role in the evaluation of the bony structure; however, assessment of the neural contents on MRIs is important for the appropriate diagnosis and treatment of patients with a narrow duplicated IAC. We report a case of a unilateral narrow duplicated IAC, with a particular emphasis on the imaging findings of thin-slice high-resolution CTs and MRIs.

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Figure 1.

High-resolution computed tomograms of the left temporal bone. Two narrow (<1 mm) bony canals are identified in the temporal bone. The anterior canal (A, arrow) continues to the bony canal of the facial nerve, and the posterior canal (B, arrow) continues to the cochlea on transverse images. There is a rudimentary posterior semicircular canal. Two separate canals (C, arrows) are well depicted on sagittal reconstructed images perpendicular to the internal auditory canal. Oval window atresia (D, arrow) is also seen on the coronal reconstructed image.

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Figure 2.

Magnetic resonance constructive interference in steady state images of the inner ear. A single thin cranial nerve can be identified in the anterior canal (A, arrow), probably implying a normal facial nerve. No nerve can be found in the posterior canal (B, arrow), suggesting a hypoplastic vestibulocochlear nerve.

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