title: Internal auditory canal morphology in children with cochlear nerve deficiency.
abstract: OBJECTIVE
  To describe the internal auditory canal (IAC) and inner ear morphologic characteristics of children with cochlear nerve (CN) deficiency.
  
  
  METHODS
  Retrospective case series.
  
  
  METHODS
  Tertiary referral center.
  
  
  METHODS
  Fourteen children with small or absent (deficient) CNs have been identified by means of high-resolution magnetic resonance imaging (MRI).
  
  
  METHODS
  MRI of the brain. Clinical evaluation.
  
  
  METHODS
  Review of medical records, audiological testing results, and imaging studies. Images were evaluated for the structure of the cochlear, vestibular and facial nerves, IACs and inner ears. Audiometric thresholds were evaluated in all subjects.
  
  
  METHODS
  Fourteen children with small or absent (deficient) CNs have been identified by means of high-resolution MRI. A review of the medical records, audiologic testing results, and imaging studies was undertaken. The images were evaluated for the structure of the cochlear, vestibular and facial nerves, IACs, and inner ears. The audiometric thresholds were evaluated in all subjects.
  
  
  RESULTS
  Among the 14 patients, 5 had known syndromes. MRI allowed an exact specification of the nervous structures within all ears with normal-size IACs. Precise characterization of the nerves in ears with small IACs was more difficult, requiring a consideration of both imaging findings and functional parameters. Five children had bilateral deficient CNs, whereas the remaining 9 subjects were affected unilaterally. Thus, 19 ears had CN deficiency (absent CN, 16; small CN, 3). Eleven ears had normal-size IACs and deficient CNs. Of the 9 ears with small IACs, 8 had deficient CNs (absent, 7; small, 1) on the basis of both MRI and functional assessments. Two ears with small IACs had clear morphologic and/or functional evidence for the presence of a CN: one had a small-size CN on MRI, whereas another had a single nerve in a small IAC with present facial and auditory functions.
  
  
  CONCLUSIONS
  The findings of this study suggest that CN deficiency is not an uncommon cause of congenital hearing loss. The findings that most ears with CN deficiency had normal IAC morphology and that two ears with small IACs had CNs present indicate that IAC morphology is an unreliable surrogate marker of CN integrity. On the basis of these findings, we think that high-resolution MRI, rather than CT imaging, should be performed in all cases of pediatric hearing loss, especially in those cases where profound hearing loss has been documented. For ears with small IACs, the resolution of MRI currently remains limiting. In these cases, the determination of CN status frequently requires a variety of anatomic (CT and MRI) and functional tests (auditory brainstem response, otoacoustic emissions, behavioral audiometry, and physical examination).
authors.affiliation: Department of Otolaryngology-Head and Neck Surgery, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7600, USA.
authors.forename: Oliver F
authors.initials: OF
authors.lastname: Adunka
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Roush
authors.forename: Holly F B
authors.initials: HF
authors.lastname: Teagle
authors.forename: Carolyn J
authors.initials: CJ
authors.lastname: Brown
authors.forename: Carlton J
authors.initials: CJ
authors.lastname: Zdanski
authors.forename: Valerie
authors.initials: V
authors.lastname: Jewells
authors.forename: Craig A
authors.initials: CA
authors.lastname: Buchman
mesh_terms: D001299:Audiometry / Q000379:methods; D002648:Child; D002675:Child, Preschool; D003056:Cochlear Nerve / Q000002:abnormalities / Q000473:pathology*; D007758:Ear, Inner / Q000002:abnormalities* / Q000033:anatomy & histology* / Q000294:innervation; D005260:Female; D034381:Hearing Loss / Q000151:congenital* / Q000209:etiology / Q000534:rehabilitation; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008279:Magnetic Resonance Imaging; D008297:Male; D012189:Retrospective Studies; D014057:Tomography, X-Ray Computed; D000160:Vestibulocochlear Nerve Diseases / Q000150:complications / Q000175:diagnosis* / Q000473:pathology