This is a presentation on the Congenital Malformations of the Inner Ear. This PPT contains a brief embryology to understand the abnormalities of the different parts of inner ear during the development. The Classification of malformations is given which has been taken from a renowned reference book. For better understanding flowcharts and figures are included. Supportive radiological images for every malformation has been included for clinical knowledge and better understanding of the malformations.

1. Congenital malformations of
Inner Ear
Dr. Dhwani Mehta (M.S. ENT)

2. Embryology of Inner Ear

3. • Initially inner ear develops independently of
middle and external ear, although become
interconnected by stapes superstructure,
attached to footplate.
• Initial development of generalized structure of
membranous labyrinth followed by
encasement by bony labyrinth and production
of series of perilymphatic spaces within bony
shell

5. • In 3rd week, Ectodermal thickening(otic
placode) on side of the developing head 
deepens  sinks below the surface forming
otic pit  eventually loses connection with
surface  forms otocyst
• Ventral part forms  cochlea, saccule
dorsal part forms  utricle, SCC

6. • The SCCs start to develop at around 5th week
as 3 flattened pouches growing at right angles
from each other from utricle  at the center
opposing epithelial surfaces fuse, coalesce,
get replaced by mesoderm around 6th week
• Simultaneously Saccule gets separated from
utricle and starts to put a single pouch like
process which coils from base to apex and
complete its full 2.5 turns of cochlea

9. Congenital Malformations of
Inner Ear

10. • In Congenital SNHL, approximately 20% of
inner ears demonstrate a radiographically
detectable abnormality.
• Many patterns of deformity appear to result
from disturbance in the embryogenesis of the
inner ear during the first trimester.

11. • Enlargement of the vestibular aqueduct is the
most common anomaly,
f/b
SCC and Cochlear deformities.

12. Mid-modiolar view
Section passing through
round window niche

13. Classification of Congenital Inner Ear
Malformations

14.  Limited to membranous labyrinth
1. Complete membranous labyrinthine dysplasia
 extremely rare
 Involves entire labyrinth including SCC, utricle,
saccule and cochlea.

15. 2. Limited membranous labyrinthine dysplasia
 Cochleosaccular dysplasia (Schelbe)
 Incomplete development of the pars inferior
 Pathologic findings confined to cochlea and
saccule (like missing Organ of Corti, collapsed
cochlear duct, degenerated stria vascularis,
collapsed saccule)
 Cochlear changes are severe in basal turn and
gradually lessen in intensity towards apex
 SCC and utricle are normal

16.  Cochlear basal turn dysplasia
 Dysplasia limited to the basal turn of cochlea
 May be related to familial high frequency SNHL
 Minimally symptomatic with normal hearing

17. Malformations of osseous and membranous labyrinth
1. Complete labyrinthine aplasia(Michel)
2. Cochlear anomalies
 Cochlear aplasia
 Cochlear hypoplasia
 Incomplete partition(Mondini)
 Common cavity
3. Labyrinthine anomalies
 SCC aplsia
 SCC dysplasia
4. Aqueductal anomalies
 Enlargement of the vestibular aqueduct
 Enlargement of the cochlear duct
5. IAC anomalies
 Narrow IAC (<3 mm)
 Wide IAC(>10 mm)
6. 8th nerve anomalies
 Hypoplasia
 Aplasia

18. 1. Complete labyrinthine
aplasia(Michel aplasia)
• Most severe deformity, exceedingly rare
• Developmental arrest occurs before the
formation of otic vesicle resulting in
complete absence of inner ear structures
• Reported in a/w thalidomide exposure &
anencephaly
• Often confused with labyrinthine ossification (
see the size of otic capsule)
• Deaf ear

19. NORMAL CT OF INNER EAR COMPLETE LABYRINTHINE APLASIA

20. 2. Cochlear anomalies
Cochlear aplasia
Completely absent cochlea
Due to arrest in the development of the cochlear
bud at the 5th week of gestation
Rare
Radiographically only SCC and vestibule are
present.
Deaf ear

22. Cochlear hypoplasia
Arrest in 6th week of gestation consists of a
single turn or less
Radiographically a small bud(1-3 mm) protruding
from vestibule
Vestibule is frequently enlarged with
accompanying SCC malformations
Hearing is variable according to the development
within truncated cochlear lumen

24. • CH-I: cochlea with smaller external dimensions with
internal architecture (modiolus and ISS) absent, and with or
without a thin bony partition between the cochlea and the
IAC. This is the most severe form of CH.
• CH-II: cochlea with smaller external dimensions with partial
modiolar development.
• CH-III: cochlea with smaller external dimensions, and
normal internal architecture.
• CH-IV: cochlea with smaller external dimensions,normal
basal turn, hypoplastic middle and apical turn.

25. Incomplete partition
• Incomplete partition anomalies represent a
group of cochlear malformations, where there
is a clear differentiation between cochlea and
vestibule, with normal external dimensions
and various internal architecture defects.

26. (a)- Incomplete partition type I (IP-I)
• clear differentiation between cochlea and vestibule
• Cochlea is located in its usual location in the
anterolateral part of the fundus of the IAC and lacks
the entire modiolus and interscalar septa
• defective stapes footplate and CSF filling the cochlea
causing recurrent meningitis  very characterstic for
IP-I

27. • They are almost always candidates for CI
as size of the cochlea is normal.

28. (b)-Incomplete partition type II (IP-II)
• The apical part of the modiolus and the corresponding
interscalar septa are defective, giving the apex of the
cochlea a cystic appearance due to the confluence of
middle and apical turns.
• The external dimensions of the cochlea are similar to that
seen in normal.
• together with a minimally dilated vestibule and an enlarged
vestibular aqueduct (EVA) constitute the triad of the
Mondini deformity.
• Modiolar defects may be due to high CSF pressure
transmission into the inner ear as a result of EVA

30. • At a young age, these patients may have near
normal hearing and may not require
amplification initially. With fluctuations and
progressive hearing loss, they become
candidates for hearing aid.
• Usually the progression in hearing loss
continues, ultimately creating a need for CI at
some point in the future.

31. (c)- Incomplete partition type III (IP-III)
• Cochlea in IP-III has interscalar septa but the
modiolus is completely absent
• cochlear otic capsule around the membranous
labyrinth is thinner when compared to that in a
normal cochlea(Instead of the usual three layers,
probably the second and third layers are either
absent. Innermost endosteal layer appears to be
thickened without enchondral and outer periosteal
layers)

33. • Patients with moderate to severe mixed or SNHL
can be managed with hearing aids.
• Patients with severe HL are candidates for CI.
Because of the absent modiolus and large defect at
the cochlear base, there is a very high chance of
electrode misplacement into IAC.
• All IP-III cases have excellent cochlear nerves.
Therefore, ABI is not indicated in this group of
incomplete partitions.

35. Classification of modiolar defects. (A) Normal modiolus (Type I), (B) shortened modiolus (Type II),
(C) enlarged SV (Type III), (D) superior modiolar defect (Type IV), (E) partial modiolar defect (Type
V), (F) subtotal modiolar defect (Type VI), (G) complete absence of the modiolus (Type VII).

36. Common cavity
Arrest at 4th week otocyst stage resulting in a
deformed inner ear where cochlea and vestibule
are confluent forming an ovoid cystic space
without internal architecture
Which is Typically longer horizontally(10 mm)
than vertically(7 mm)
Can be misdiagnosed as dysplastic lateral SCC
(relation with IAC)

37. Neural population sparse or absent
Hearing invariably is poor
For CI surgery, the surgical approach is via a
transmastoid Labyrinthotomy with a straight (non-
modiolar hugging) electrode. This will have a
position on the periphery of the CC with better
contact with the neural tissue.

40. • Rudimentary otocyst: Between the 3rd and 4th
week, the inner ear is in the form of an otocyst
(otic vesicle).
• This pathology represents an anomaly between a
Michel deformity and common cavity (CC).
– IAC is usually absent

41. • There is no connection between the otocyst
and the brainstem is a contraindication to CI
surgery. Rudimentary otocyst is a definite
indication for ABI.

42. 3. Labyrinthine anomalies
SCC dysplasia
Dysplasia of lateral SCC is common (40%) as it forms
earlier in embryogenesis
During the 6th week of development, the budding SCC
normally forms the semicircular evagination from the
vestibular anlage
Central portion of pocket shaped protrusion adheres, leaving a
peripheral semicircular tube
Absence of this central adhesion results in SCC dysplasia

44. Typical radiographic appearance is that of a
short, broad cystic space confluent with
vestibule
Rudimentary crista ampullaris
Caloric response are functionally absent with
normal hearing if cochlea is normal

45. SCC aplasia
Failure in the development of vestibular anlage
before 6th week of gestation
CHARGE syndrome

46. 4. Malformations of Vestibular and
Cochlear Aqueduct
Enlargement of vestibular aqueduct
Most common radiographically detectable malformation
of inner ear
The diameter of normal VA - 0.4 to 1 mm
enlarged VA - >2 mm
 presence of an enlarged vestibular aqueduct
(i.e. the midpoint between posterior labyrinth and
operculum is larger than 1.5 mm) in the presence of a
normal cochlea,vestibule and SCCs.
 Difference between EVA and IP-II is that cochlea and
vestibule are completely normal on HRCT and MRI.

48. Enlargement of cochlear aqueduct
– associated with stapedectomy gusher and
transotic csf leak

50. Thank You