We present a case of an otherwise healthy 20-month-old with congenital sensorineural hearing loss. CT and MR imaging demonstrated bilateral asymmetrically severe hypoplasia of the internal auditory canals and vestibulocochlear nerves. Additional developmental inner ear anomalies were present in this patient, including unilateral semicircular canal hypoplasia and suspected bilateral cochlear hypoplasia. The patient retained normal facial nerve function bilaterally. We highlight the current research and understanding of congenital IAC abnormalities

Djalilian, Hamid R

Floriolli, David

Hasso, Anton

Martin, Jeremy W

Senturk, Cagin

Thompson, Matthew

Wishka, Christian

English

eScholarship - University of California

Asymmetrically severe internal auditory canal hypoplasia: A case report.

Martin, Jeremy

Djalilian, Hamid

UC IrvineUC Irvine Previously Published WorksTitleAsymmetrically severe internal auditory canal hypoplasia: A case report.Permalinkhttps://escholarship.org/uc/item/2md0h0m5JournalRadiology Case Reports, 15(5)ISSN1930-0433AuthorsMartin, JeremyWishka, ChristianThompson, Matthewet al.Publication Date2020-05-01DOI10.1016/j.radcr.2020.01.037 Peer reviewedeScholarship.org Powered by the California Digital LibraryUniversity of CaliforniaR a d i o l o g y  C a s e  R e p o r t s  1 5  ( 2 0 2 0 )  4 5 7 – 4 5 9  Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/radcr Case Report Asymmetrically severe internal auditory canal hypoplasia: A case report Jeremy W. Martin a , Christian Wishka, DO a , ∗, Matthew Thompson, MD a , Hamid R. Djalilian, MD b , David Floriolli, MD a , Cagin Senturk, MD a , Anton Hasso, MD a a Department of Radiology, University of California, Irvine; 101 The City Drive, Orange, CA 92868, USA b Department of Otolaryngology, University of California, Irvine; 101 The City Drive, Orange, CA 92868, USA a r t i c l e i n f o Article history: Received 24 October 2019 Revised 22 January 2020 Accepted 25 January 2020 Keywords: Sensorineural hearing loss SNHL Internal auditory canal hypoplasia Neuroradiology Incomplete partition a b s t r a c t We present a case of an otherwise healthy 20-month-old with congenital sensorineural hearing loss. CT and MR imaging demonstrated bilateral asymmetrically severe hypopla- sia of the internal auditory canals and vestibulocochlear nerves. Additional developmental inner ear anomalies were present in this patient, including unilateral semicircular canal hypoplasia and suspected bilateral cochlear hypoplasia. The patient retained normal facial nerve function bilaterally. We highlight the current research and understanding of congen- ital IAC abnormalities. © 2020 The Authors. Published by Elsevier Inc. on behalf of University of Washington. This is an open access article under the CC BY-NC-ND license. ( http://creativecommons.org/licenses/by-nc-nd/4.0/ )                       Case report A 20-month-old female, born 37 weeks gestation, was re-ferred to our institution for sensorineural hearing loss. Thepatient had no known significant pertinent birth or perinatalmedical history. The patient had no facial dysmorphismand demonstrated normal facial nerve function. The patientdemonstrated abnormal auditory brainstem response testingbeginning at age of 4 months. At the time of initial referral toour center, she had been using hearing aids for nearly 1 year.On clinical examination, she did not yet ambulate indepen-dently, limiting clinical assessment of gait and equilibrium.She responded only to loud noises while using hearing aidsand exhibited delayed spoken language development. ∗ Corresponding author. E-mail address: cwishka@hs.uci.edu (C. Wishka). https://doi.org/10.1016/j.radcr.2020.01.037 1930-0433/© 2020 The Authors. Published by Elsevier Inc. on behalf of UCC BY-NC-ND license. ( http://creativecommons.org/licenses/by-nc-nd/CT and MRI were performed as part of her workup, bothof which demonstrated bilateral asymmetrically severe innerear abnormalities. The right side was more severely involved,exhibiting nonvisualization of both the internal auditorycanal and vestibulocochlear nerve ( Fig. 1 ), compatible withsevere hypoplasia/aplasia of both structures. On the left, a hy-poplastic internal auditory canal was seen, with questionablevisualization of a hypoplastic vestibulocochlear nerve ( Fig. 2 ).A few associated findings were also noted. A normal parti-tion of the cochlea and vestibule was seen bilaterally, thoughthe bilateral vestibules were enlarged ( Fig. 3 ). There wasniversity of Washington. This is an open access article under the 4.0/ ) 458 R a d i o l o g y  C a s e  R e p o r t s  1 5  ( 2 0 2 0 )  4 5 7 – 4 5 9  Fig. 1 – Heavily T2-weighted coronal MRI of the skull base centered at the expected region of the internal auditory canals: 4.0 mm multiplanar reconstruction of 0.5 mm slices. There is nonvisualization of the right internal auditory canal and vestibulocochlear nerve, compatible with severe hypoplasia/aplasia. Fig. 2 – Heavily T2-weighted (A) axial, (B) coronal, and (C) sagittal MRI reconstructions of the skull base centered at the expected region of the internal auditory canals. The left internal auditory canal is hypoplastic, measuring a minimum vertical diameter of approximately 0.9 mm. Faint wispy internal intermediate signal within the narrow canal may reflect a poorly visualized hypoplastic left vestibulocochlear nerve. Fig. 3 – Axial T2-weighted MRI of the skull base. There is enlargement of the bilateral vestibules. There is possible bilateral cochlear hypoplasia, with the appearance of 1.5 turns. Fig. 4 – Coronal CT of the bilateral inner ear structures. The right lateral semicircular canal is intact (blue arrow), while the left lateral semicircular canal terminates as a hypoplastic short, wide trunk (red arrow). The remainder of the semicircular canals are normal in appearance (not imaged). From an embryological perspective, the lateral semicircular canal is expected to be the first malformed canal in the spectrum of inner ear developmental anomalies [11] . (Color version of figure is available online.)             suspected cochlear hypoplasia with 1.5 turns of the cochleabilaterally ( Fig. 3 ). The left lateral semicircular canal wasnoted to be hypoplastic ( Fig. 4 ). There was no enlargement ofthe endolymphatic sacs bilaterally. After obtaining the above imaging, the patient was docu-mented in our electronic health record as pending cochlearimplant consultation. No further clinical management hasbeen since documented at the time of writing. Discussion Congenital sensorineural hearing loss (SNHL) affects 1 in 1000newborns and represents a barrier to normal speech andlanguage development in the affected child. Approximately20%-35% patients with congenital SNHL have visualizedabnormalities of the inner ear [1] . High resolution CT and MRIof the temporal bones and IAC is recommended to adequatelyR a d i o l o g y  C a s e  R e p o r t s  1 5  ( 2 0 2 0 )  4 5 7 – 4 5 9  459                                      assess osseous anatomy, fluid spaces, and integrity of thevestibulocochlear nerve (VCN). A vertical IAC diameter of less than 2 mm is generally con-sidered the definition for IAC hypoplasia [2] . IAC abnormalitiesare frequently accompanied by hypoplasia/aplasia of the VCN,with 92% of IAC malformations exhibiting aplasia of the VCNin a case series [5] . The facial nerve, however, may retain func-tionality in the setting of IAC atresia (as in this case) by takingan aberrant superoventral course [6] . Such a course was notdirectly visualized on imaging in this patient. The IAC develops from mesoderm enveloping the VCN,which eventually transforms into cartilage and ossifies.Current understanding suggests that development of theIAC is intricately associated with that of the VCN; atresia orhypoplasia of IAC is likely a result of altered VCN develop-ment secondary to faulty chemotactic mechanisms or lackof end organ targets [3,7] . While FGF3 mutations have beenlinked to IAC and other inner ear structural abnormalities,the molecular genetics governing these abnormalities remainpoorly defined. It is believed that bilateral symmetric casesare usually associated with genetic factors, whereas asym-metric cases, such as seen in this patient, may be more likelydue to external insults [8] . IAC hypoplasia/atresia has been associated with otherinner ear abnormalities [4] , such as incomplete partitionvariants, cochlear and semicircular canal hypoplasia, andcomplete labyrinthine aplasia (Michel aplasia). Numerousclassification systems have been proposed to account for themyriad presentations of inner ear malformations, which willnot be discussed here [9–11] . In addition to bilateral asymmet-ric IAC hypoplasia/atresia, this patient had left semicircularcanal hypoplasia and suspected bilateral cochlear hypoplasia.CT and MR imaging of the temporal bone should beperformed prior to cochlear implantation to assess the os-seous anatomy, fluid spaces, and integrity of the VCN. Theabsence of a VCN has generally been considered a relativecontraindication to cochlear implants [12] . Auditory brain-stem implantation may represent a therapeutic alternativefor these patients. R E F E R E N C E S  [1] Joshi VM , Navlekar SK , Kishore GR , Reddy KJ , Kumar EC . CT and MR imaging of the inner ear and brain in children with congenital sensorineural hearing loss. Radiographics 2012;32:683–98 .[2] 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 .[3] Romo LV, Casselman JW, Robson CD. Temporal bone: congenital anomalies. In: Som PM, Curtin HD, eds. Head and neck imaging. 4th ed. Vol 2. St Louis, Mo: Mosby, 2003; 1119–1140.[4] Sakina MS , Goh BS , Abdullah A , Zulfiqar MA , Saim L . Internalauditory canal stenosis in congenital sensorineural hearing loss. Int J Pediatr Otorhinolaryngol 2006;70:2093–7 .[5] Giesemann AM , Kontorinis G , Jan Z , Lenarz T , Lanfermann H ,Goetz F . The vestibulocochlear nerve: aplasia and hypoplasiain combination with inner ear malformations. Eur Radiol 2012;22:519–24 .[6] Giesemann AM , Neuburger J , Lanfermann H , Goetz F . Aberrant course of the intracranial facial nerve in cases of atresia of the internal auditory canal (IAC). Neuroradiology 2011;53:681–7 .[7] Ferreira T , Shayestehfar B , Lufkin R . Narrow, duplicated internal auditory canal. Neuroradiology 2003;45:308–10 .[8] Sennaroglu L , Saatci I . A new classification for cochleovestibular malformations. Laryngoscope 2002;112:2230–41 .[9] Sennaro ̆glu L. Classification and current management of inner ear malformations. 2017;34:397-411.[10] Adibelli ZH , Isayeva L , Koc AM , Catli T , Adibelli H , Olgun L . The new classification system for inner ear malformations: the INCAV system. Acta Otolaryngol 2017;137:246–52 .[11] Jackler RK , Luxford WM , House WF . Congenital malformations of the inner ear: a classification based on embryogenesis. Laryngoscope 1987;97(Suppl 40):2 .[12] Tahir E , Bajin MD , Atay G , Mocan BO , Sennaroglu L . Bony cochlear nerve canal and internal auditory canal measures predict cochlear nerve status. J Laryngol Otol 2017;131:676–83 .

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Asymmetrically severe internal auditory canal hypoplasia: A case report.

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