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.
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Usage
An imaging-based classification was first proposed in 1987 by Jackler et al. according to polytomography findings and embryological concepts 1. Using CT, Sennaroglu & Bajin later refined the classification proposed by Jackler et al. in 2017 and its pathophysiological basis 2-4 and is the most used worldwide (c.2019) 4-6.
Classification
Sennaroglu classification
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complete labyrinthine aplasia (Michel deformity)
with hypoplastic or aplastic petrous bone
without otic capsule
with otic capsule
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with normal (vestibular) labyrinth
with dilated vestibule
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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)
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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)
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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 3rd week (for complete labyrinthine aplasia) and 7th week (for incomplete partition type II), with the exception that incomplete partition type I is posited to occur earlier than cochlear hypoplasia 2 and common cavity is sometimes listed earlier than cochlear aplasia 3.
Associations
The above classification does not separately account for findings that may occur in association with other inner ear malformations but are sometimes isolated 2,5:
vestibule dilation
internal auditory canal abnormalities
In addition to the above categories of findings, which are primarily based on CT, abnormalities of the cochlear nerve are important to identify on MRI 4,5:
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 7, 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).