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 Table of Contents  
CASE REPORT
Year : 2022  |  Volume : 28  |  Issue : 1  |  Page : 84-87

Unilateral double-barreled internal auditory meatus with severe sensorineural hearing loss: A diagnostic challenge


1 Department of Otorhinolaryngology, SRM Medical College Hospital and Research Centre, Chengalpattu, Tamil Nadu, India
2 Department of Radiology, SRM Medical College Hospital and Research Centre, Chengalpattu, Tamil Nadu, India

Date of Submission26-Oct-2021
Date of Acceptance03-Dec-2021
Date of Web Publication25-Apr-2022

Correspondence Address:
Dr. R Vaishnavi
Department of Otorhinolaryngology, SRM Medical College Hospital and Research Centre, SRM Nagar, Potheri, Chengalpattu - 603 203, Tamil Nadu
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/indianjotol.indianjotol_154_21

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  Abstract 


Internal auditory meatus duplication is an exceedingly rare temporal bone anomaly. All of them being bilateral duplication or narrowing of internal auditory meatus with profound sensorineural hearing loss. We report a very rare case of unilateral double-barreled internal auditory meatus with severe sensorineural hearing loss without any inner ear anomalies in an adolescent, being benefited with an air conduction hearing aid.

Keywords: Cochlear nerve hypoplasia, inferior vestibular nerve hypoplasia, internal auditory meatus duplication, magnetic resonance imaging


How to cite this article:
Selvarajan G, Vaishnavi R, Prateep MA, Jeevanandham B. Unilateral double-barreled internal auditory meatus with severe sensorineural hearing loss: A diagnostic challenge. Indian J Otol 2022;28:84-7

How to cite this URL:
Selvarajan G, Vaishnavi R, Prateep MA, Jeevanandham B. Unilateral double-barreled internal auditory meatus with severe sensorineural hearing loss: A diagnostic challenge. Indian J Otol [serial online] 2022 [cited 2022 Nov 29];28:84-7. Available from: https://www.indianjotol.org/text.asp?2022/28/1/84/343754




  Introduction Top


Duplication of the internal auditory canal is a very rare congenital disorder of temporal bone which is usually bilateral, associated with cochlear and inferior vestibular nerve hypoplasia.[1] Only 14 cases have been reported so far.[2] Congenital sensorineural hearing loss associated with inner ear anomalies is 20% more common with internal auditory meatus stenosis.[3] The normal diameter of internal auditory meatus is 2–8 mm, and in stenosis, it is <2 mm. The duplicated internal auditory canal is frequently misdiagnosed as internal auditory canal stenosis. Patients with stenotic internal auditory canal have dysplastic cochlear and vestibular nerve, whereas duplicated internal auditory canal will have aplasia of cochlear and inferior vestibular nerve.[2] The management of hypoplastic cochlear nerve would be a cochlear implant,[4] but in case of an aplastic nerve cochlear implant would not be beneficial.[2] This case is of a unilateral double-barreled internal auditory canal with severe sensorineural hearing loss, which has not been reported in the literature so far. The inferior contents of internal auditory canal, the cochlear and the inferior vestibular nerve were hypoplastic due to the duplication of internal auditory canal.


  Case Report Top


An 11-year-old boy presented with a right-sided hearing loss for 6 months. He noticed right ear hard of hearing while using his headphones. He had no history of ear discharge, dizziness, or facial asymmetry. His birth and developmental history were normal. He had no significant family history of hearing loss. Otoscopic examination showed bilateral tympanic membranes intact. The tuning fork test showed a false-negative Rinne's on the right side and positive on the left side with the weber lateralized to the left ear.

Radiological evaluation: High-resolution computed tomography (CT) of the temporal bone in sagittal view [Figure 1] uncovers the right double-barreled internal auditory canal and normal internal auditory canal on the left side [Figure 2]. Magnetic resonance imaging (MRI) [Figure 3] showed right cochlear nerve and inferior vestibular nerve extremely thinned out with normal findings on the left side [Figure 4]. A three-dimensional reconstruction of bilateral internal auditory canal elicited the same findings [Figure 5].
Figure 1: High-resolution computed tomography temporal bone coronal view on the right side showing double-barrelled internal auditory canal

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Figure 2: High-resolution computed tomography temporal bone sagittal view comparing both internal auditory canal, black arrow indicating right double-barreled internal auditory canal, normal internal auditory canal on the left side

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Figure 3: Magnetic resonance imaging of the inner ear sagittal view comparing right double-barreled internal auditory canal. White arrow indicates the hypoplastic cochlea and inferior vestibular nerve, normal internal auditory canal on the left side with normal inferior vestibular and cochlear nerve

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Figure 4: Comparison of magnetic resonance imaging (sagittal view) of bilateral internal auditory canal of same patient: White arrow showing the absence of cochlear and inferior vestibular nerve on the right side while showing cochlear, inferior, and superior vestibular nerve on the left

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Figure 5: Three-dimensional reconstruction comparing both internal auditory canal, black arrow indicating right double-barreled internal auditory canal, normal internal auditory canal on the left side

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Audiological evaluation: A pure-tone audiogram showed right severe sensorineural hearing loss with left side normal hearing. Tympanometry showed “A” type curve on both the ears. Oto Acoustic Emission was absent on the right ear. A brain stem-evoked potential [Figure 6] showed severe sensorineural hearing loss in the right ear with normal hearing in the left ear. Cervical vestibular evoked myogenic potentials showed P13, N23 peak and were observed within normal limits and the peak amplitude was reduced in the right ear [Figure 7]. The ocular vestibular evoked myogenic potentials N10, P15 peaks were observed within normal limits but the peak amplitude was enhanced in both the ears [Figure 8]. The patient found an improvement in his hearing with an air conduction hearing aid.
Figure 6: Auditory brain stem response

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Figure 7: Cervical vestibular-evoked myogenic potential

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Figure 8: Ocular vestibular-evoked myogenic potential

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  Discussion Top


Double-barreled internal auditory canal is a very rare congenital disorder of temporal bone which is usually bilateral, associated with cochlear and inferior vestibular nerve hypoplasia.[1] Previous studies have shown that 20% of such cases were associated with inner ear anomalies whereas our case being an exception was unilateral and without anomalies. There is a case report of internal auditory canal stenosis with facial palsy in a 3 year old.[8] The cervical and ocular vestibular-evoked myogenic potentials showed minimal peak amplitude on the right side and enhanced peak amplitudes on both the sides, respectively, even though brain stem-evoked potential was absent on the right side. In previous case reports, the cervical and ocular vestibular-evoked myogenic potentials were normal with absent response on brain stem evoked potential.

Internal auditory canal anomalies are atresia, stenosis, and hypoplasia. It is believed that there are two theories for internal auditory canal stenosis. The first most accepted theory states that embryonic cochlea induces the growth of the vestibulocochlear nerve and the bony canal develops around the eighth nerve through the mesoderm chondrification and ossification.[5] If the eighth nerve is hypo plastic or aplastic the internal auditory canal development is also impaired. The second hypothesis states that bony defect inhibits the growth of eighth cranial nerve by narrowing of the internal auditory canal. The second theory fails to explain about the preservation of facial nerve.[7] High-resolution CT of temporal bone is highly sensitive and specific for the identification of bony abnormalities and helps in the detection of inner ear abnormalities. However, in case of internal auditory canal duplication, it fails to identify the neural structures in the internal auditory canal.[6]

This is the first case in the literature of unilateral internal auditory canal duplication with severe sensorineural hearing loss where an air conduction hearing aid was helpful, as the 14 cases which have been reported so far involve bilateral duplication/stenosis of internal auditory canal with profound hearing loss.

The approach for any case of unilateral sensorineural hearing loss in an adolescent age group should be a complete history, physical examination, audiometric tests, and high-resolution CT is preferred in case of unilateral significant hearing loss than an MRI.

Informed consent

Informed consent was obtained from the patient.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given his consent for his images and other clinical information to be reported in the journal. The patient understands that name and initials will not be published and due efforts will be made to conceal identity, but anonymity cannot be guaranteed.

Compliance with ethical standards

Yes.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
Valvassori GE, Pierce RH. The normal internal auditory canal. Am J Roentgenol Radium Ther Nucl Med 1964;92:1232-41.  Back to cited text no. 1
    
2.
Vilain J, Pigeolet Y, Casselman JW. Narrow and vacant internal auditory canal. Acta Otorhinolaryngol Belg 1999;53:67-71.  Back to cited text no. 2
    
3.
Nakamura K, Koda J, Koike Y. Stenosis of the internal auditory canal with VIIth and VIIIth cranial nerve dysfunctions. ORL J Otorhinolaryngol Relat Spec 1999;61:16-8.  Back to cited text no. 3
    
4.
Vincenti V, Ormitti F, Ventura E. Partitioned versus duplicated internal auditory canal: When appropriate terminology matters. Otol Neurotol 2014;35:1140-4.  Back to cited text no. 4
    
5.
Yates JA, Patel PC, Millman B, Gibson WS. Isolated congenital internal auditory canal atresia with normal facial nerve function. Int J Pediatr Otorhinolaryngol 1997;41:1-8.  Back to cited text no. 5
    
6.
Winslow CP, Lepore ML. Imaging quiz case 1. Bilateral agenesis of lateral semicircular canals with hypoplasia of the left internal auditory canal (IAC). Arch Otolaryngol Head Neck Surg 1997;123:1236, 1238-9.  Back to cited text no. 6
    
7.
Casselman JW, Offeciers FE, Govaerts PJ, Kuhweide R, Geldof H, Somers T, et al. Aplasia and hypoplasia of the vestibulocochlear nerve: Diagnosis with MR imaging. Radiology 1997;202:773-81.  Back to cited text no. 7
    
8.
Park SH, Kim WJ, Lim YJ, On CW, Park JH, Min EH. Rare occurrence of internal auditory canal stenosis accompanied with congenital facial palsy in a 3-month-old infant: A case report. Ann Rehabil Med 2020;44:256-9.  Back to cited text no. 8
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]



 

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