Inner ear malformations (classification)

Inner ear malformations are a spectrum of congenital anomalies involving the inner ear structures with an emphasis on the cochlea due to their implications for sensorineural hearing loss.


An imaging-based classification was first proposed in 1987 by Jackler et al. according to polytomography findings and embryological concepts . Using CT, Sennaroglu et al. later refined the classification and its pathophysiological basis . The latest (2017) iteration of Sennaroglu's classification, which is the most used worldwide, is as follows :

  • complete labyrinthine aplasia (Michel deformity)
  • with hypoplastic or aplastic petrous bone
  • without otic capsule
  • with otic capsule
  • rudimentary otocyst
  • cochlear aplasia
  • with normal (vestibular) labyrinth
  • with dilated vestibule
  • common cavity
  • cochlear hypoplasia
  • bud-like cochlea (CH-I)
  • cystic hypoplastic cochlea (CH-II)
  • cochlea with less than 2 turns (CH-III)
  • cochlea with hypoplastic middle and apical turns (CH-IV)
  • incomplete partition of the cochlea
  • incomplete partition type I (IP-I; cystic cochleovestibular anomaly)
  • incomplete partition type II (IP-II; including as part of the Mondini malformation)
  • incomplete partition type III (IP-III; X-linked deafness)
  • enlarged vestibular aqueduct
  • cochlear aperture abnormalities
  • hypoplasia
  • aplasia
  • Items 1 through 6 above represent a spectrum ordered from the least to most differentiated inner ear structures due to the time of developmental arrest ranging between the 3week (for complete labyrinthine aplasia) and 7 week (for incomplete partition type II), with the exception that incomplete partition type I is posited to occur earlier than cochlear hypoplasia and common cavity is sometimes listed earlier than cochlear aplasia .

    The above classification does not separately account for findings that may occur in association with other inner ear malformations but are sometimes isolated :

    In addition to the above categories of findings, which are primarily based on CT, abnormalities of the cochlear nerve are important to classify by MRI :

    • hypoplastic or absent cochlear nerve
    • hypoplastic or absent common cochleovestibular nerve

    Radiology report

    Because of the complex and variable associations of individual components of these inner ear malformations, some have proposed a finely descriptive approach to reporting. In the INCAV classification system , imaging abnormalities are graded by severity for each of the major inner ear structures: internal auditory canal (I), cochlear nerve on MRI or cochlear nerve canal on CT (N), cochlea (C), vestibular aqueduct (A), and vestibule (V). For example, the cochlea may be classified as normal (0), incomplete partition type II (1), incomplete partition type III (2), hypoplasia (3), incomplete partition type I (4), common cavity (5), or aplasia (6).

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