Korean J Radiol.  2019 May;20(5):823-829. 10.3348/kjr.2018.0065.

Duplicated Internal Auditory Canal: High-Resolution CT and MRI Findings

• Wang L
• Zhang L
• Li X
• Guo X

• KMID: 2442716
• DOI: http://doi.org/10.3348/kjr.2018.0065

Abstract

OBJECTIVE
To summarize the high-resolution computed tomography (HRCT) and magnetic resonance imaging (HRMRI) features of duplicated internal auditory canals (DIACs).
MATERIALS AND METHODS
Ear HRCT data of 64813 patients with sensorineural hearing loss (SNHL), obtained between August 2009 and November 2017, were reviewed. Among these patients, 12 (13 ears) were found to have DIACs, 9 of whom underwent HRMRI. Their images were evaluated by two otoradiologists.
RESULTS
The rate of occurrence of DIAC among SNHL patients was 0.019% (12/64813). The internal auditory canals of 13 ears were divided into double canals by complete (n = 6) and incomplete (n = 7) bony septa, with varied orientations ranging from horizontal to approximately vertical. All of the anterosuperior canals extended into the facial nerve (FN) canal, except for 1, which also extended to the vestibule. The posteroinferior canals ended in the cochlea and vestibule, except for 2, which also connected to the FN canals. Magnetic resonance images revealed that 77.8% (7/9) and 22.2% (2/9) of vestibulocochlear nerves (VCNs) were aplastic and hypoplastic, respectively. Furthermore, 88.9% (8/9) of FNs were normal, except for 1, which was hypoplastic. All of the affected ears also had other ear anomalies: a narrow, bony cochlear nerve canal was the most common other anomaly, accounting for 92.3% (12/13). Malformations of other systems were not found.
CONCLUSION
Double-canal appearance is a characteristic finding of DIAC on HRCT, and it is usually accompanied by other ear anomalies. The VCN usually appears aplastic, with a normal FN, on HRMRI.

Keyword

Internal auditory canal; Duplication; Computed tomography; Magnetic resonance imaging

MeSH Terms

Cochlea
Cochlear Nerve
Ear
Facial Nerve
Hearing Loss, Sensorineural
Humans
Magnetic Resonance Imaging*
Vestibulocochlear Nerve

Figure

• 

  Fig. 1 23-year-old male with right DIAC.A, B. Oblique coronal and parasagittal HRCT images show that IAC is divided into double canals by complete horizontal bony septum (arrows). C, D. Superior portion is connected to FN canal (arrows), whereas inferior portion is connected to cochlea and vestibule (short arrow). Ipsilateral bony CN canal is narrow (long arrow). E. CT volume rendering image shows bony septum (arrow). F–H. Oblique axial and parasagittal MRI show that right VCN (short arrow) is aplastic and FN (long arrows) is normal in cisternal segment. CN = cochlear nerve, CT = computed tomography, DIAC = duplicated internal auditory canal, FN = facial nerve, HRCT = high-resolution CT, IAC = internal auditory canal, VCN = vestibulocochlear nerve

• 

  Fig. 2 6-year-old female with left DIAC.A, B. Oblique coronal and parasagittal HRCT images clearly show complete and nearly vertical bony septum (arrows). C. Anterior canal is connected to FN canal (arrow). D. Posterior canal ends in cochlea and vestibule, and ipsilateral bony CN canal is stenotic (arrow). E. CT volume rendering image clearly shows that FN canal meatus is anteriorly and superiorly located (arrow). F–H. Oblique axial and parasagittal MR images reveal left aplastic VCN and normal FN (short arrows). Latter has migrated beneath trigeminal nerve (long arrows). MR = magnetic resonance

• 

  Fig. 3 4-month-old female with right DIAC.A, B. Oblique coronal and parasagittal HRCT images show that IAC is divided into two portions by complete oblique bony septum (arrows). C. FN canal is continuous with anterosuperior canal (short arrow) and with posteroinferior canal through accessory canal (long arrow). D. CT volume rendering image shows meatus of double canals and bony septum (arrow).

• 

  Fig. 4 8-year-old female with left DIAC.A. Oblique coronal HRCT image shows that bony septum has medial (short arrow) and lateral (long arrow) defects. B. Anterosuperior canal is connected to FN canal (short arrow) and to vestibule (long arrow). C. Posteroinferior canal ends in cochlea (short arrow) and vestibule (long arrow). D–F. Oblique axial and parasagittal MR images reveal that left dysplastic VCN (short arrows) and normal FN enter anterosuperior canal (long arrow).

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