Inner ear malformations (classification)

Cochlear anomaliesInner ear malformations  areare a varietyspectrum of congenital anomalies which, dependinginvolving the inner ear structures with an emphasis on the exact time at which an insult occurs during embryogenesis, may have different manifestations. Terminology is often used imprecisely leadingcochlea due to confusion not only among clinicians, but also in the literaturetheir implications for sensorineural hearing loss.

Classification

AThe first classification firstwas proposed in 1987 by Jackler et al.² has become widely accepted (with various modification), which divides congenital cochlear anomalies according to polytomography findings and embryogenesis ¹. Sennaroglu et al. later refined the timingclassification and its pathophysiological basis ^2-4. There is no single universally accepted classification, but the following grouping represents a synthesis of the developmental arrest. 

Conveniently starting at 3recent literature ^rd4-7 week till the end of 7^thweek of gestation, an insult during each subsequent week results in a distinct inner ear abnormality:

1. complete labyrinthine aplasia (Michel deformity)
   1. with hypoplastic or Michel deformityaplastic petrous bone
   2. without otic capsule
   3. with otic capsule
2. rudimentary otocyst: 3^rd week
3. cochlear aplasia: 4^th week
   1. with normal vestibular labyrinth
   2. with dilated vestibule
4. common cavity malformation to the cochlea and vestibule: early 5^th week
5. cochlear incomplete partition type I including cystic cochleovestibular anomaly: late 5^th week
6. cochlear hypoplasia: 6
   1. bud-like cochlea (CH-I)
   2. cystic hypoplastic cochlea (CH-II)
   3. cochlea with less than 2 turns (CH-III)
   4. cochlea with hypoplastic middle and apical turns (CH-IV)
7. incomplete partition of the cochlea
   1. incomplete partition type I (IP-I; cystic cochleovestibular anomaly)
   2. ​incomplete partition type II (IP-II; including as part of the Mondini malformation)
   3. incomplete partition type III (IP-III; X-linked deafness)

This grouping represents a spectrum ordered from the least to most differentiated inner ear structures due to the time of developmental arrest ranging between the 3^rd week (for complete labyrinthine aplasia) and 7^th week

• cochlear (for incomplete partition type II including Mondini dysplasia: 7^th week

See also

• cochlear), with the exception that incomplete partition type IIII is posited to occur earlier than cochlear hypoplasia ² and common cavity is sometimes listed earlier than cochlear aplasia ³.

  There are additional inner ear anomalies that may occur alone or in association with the above cochlear abnormalities ^4,7:

  1. enlarged vestibular aqueduct
  2. dysplastic semicircular canal
  3. hypoplastic or aplastic cochlear aperture (cochlear fossette; bony cochlear nerve canal)
  4. hypoplastic or aplastic cochlear nerve
     • type 1: completely absent cochlear nerve with stenotic internal auditory canal
     • type 2a: common vestibulocochlear nerve present, aplastic or hypoplastic cochlear nerve in the internal auditory canal, and associated inner ear anomalies
     • type 2b: deficient cochlear nerve, otherwise normal inner ear