Cochlear incomplete partition type I

Last revised by Sara Bertazzon on 27 Apr 2023

Cochlear incomplete partition type I (IP-I) is a type of cochlear anomaly associated with sensorineural hearing loss.

As with other types of incomplete partition, the cochlea is clearly differentiated from the vestibule and the external dimensions of the cochlea are nearly normal.

The following are the defining CT features of incomplete partition type I, leading to the name cystic cochleovestibular malformation 1,2:

  • cystic appearance of the cochlea due to
    • absence of the modiolus including the base/cribriform plate between the cochlea and internal auditory canal (although a thin plate not visible on imaging may be present 5)
    • absence of the interscalar septum
  • grossly dilated vestibule

This appearance has been likened to a figure 8 morphology 6.

Several features have been associated but are not universal:

  • no large vestibular aqueduct 1,4 (with exceptions 3​)
  • internal auditory canal enlargement 1 (with exceptions 4​)
  • semicircular canal dysplasia 3 (with exceptions 1​)
  • common cavity: the cochlea and vestibule are also cystic but they are not separated
  • incomplete partition type II: the cochlear apex is also cystic but the basal turn is distinctly formed and the vestibule is less dilated

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