This document discusses techniques for cochlear implantation through the middle cranial fossa approach. It describes performing a superior cochleostomy just below the origin of the greater superficial petrosal nerve. It cautions not to fear injury to the carotid artery, which is 1 cm anterior. It also details identifying structures like the facial nerve and drilling the internal auditory canal from medial to lateral to avoid injuring the cochlea. Electrodes are described being placed in the basal, middle, and apical turns of the cochlea. Facial nerve stimulation is a risk if electrodes contact the labyrinthine segment, so selective deactivation may be needed. The document emphasizes the importance of anatomical landmarks and

1. Cochlea Cadaver
Dissection- Part 2
18-04-2017
8.26 pm

2. Part-1 of this PPT
present at weblink
www.skullbase360.in

3. Middle cranial fossa
approach for
Cochlear implant

4. APICAL TURN / SUPERIOR TURN
cochleostomy in middle cranial
fossa approach
So the indication of middle cranial fossa superior
cochleostomy insertion is in infected cases after CWD
+ SP ( subtotal petrosectomy ) We can do redo by fat
risnced in rifampacin . But if you want to go by sterile
area middle cranial fossa superior cochleostomy &
reverse insertion & reverse programming

5. Superior cochleostomy in middle cranial fossa is just below origin
of GSPN Don't fear about carotid ( metal probe ) . Petrous carotid
is 1 cm anterior to origin of GSPN

6. Superior cochleostomy in middle cranial fossa is just below origin
of GSPN Don't fear about carotid ( metal probe ) . Petrous carotid
is 1 cm anterior to origin of GSPN

7. Superior cochleostomy in middle cranial fossa is just below origin
of GSPN Don't fear about carotid ( metal probe ) . Petrous carotid
is 1 cm anterior to origin of GSPN

8. Probe in Superior cochleostomy in
middle cranial fossa is just below origin
of GSPN

9. Superior cochleostomy in middle
cranial fossa is just below origin of
GSPN

10. Superior cochleostomy in middle
cranial fossa is just below origin of
GSPN

11. See the probe inserted through superior cochleostomy from
middle cranial fossa exactly corresponds to superior
cochleostomy just below tensor tympani from middle ear

12. See the probe inserted through superior cochleostomy from
middle cranial fossa exactly corresponds to superior
cochleostomy just below tensor tympani from middle ear

13. See the probe inserted through superior cochleostomy from middle cranial
fossa exactly corresponds to superior cochleostomy just below tensor
tympani from middle ear

14. See the probe inserted through superior cochleostomy
from middle cranial fossa exactly corresponds to
superior cochleostomy just below tensor tympani from
middle ear

15. Labyrinthine part of facial nerve
in middle cranial fossa

16. Just now i fractured
tegmen of middle ear with
my finger nail … it is so thin
…………..So identify ossicles
of middle ear through very
thin middle ear tegmen &
then identify horizontal
facial nerve & then 1st
genu & then labyrinthine
facial nerve ...... simplest
way to decompress
labyrinthine Or else if you
come from medically you
may injure cochlea or SSC

17. Note horizontal part of facial nerve
through middle cranial fossa as
continuation of GSPN

18. tegmen of middle ear is so thin …………..So identify ossicles of
middle ear through very thin middle ear tegmen & then identify
horizontal facial nerve & then 1st genu & then labyrinthine facial
nerve ...... simplest way to decompress labyrinthine Or else if you
come from medically you may injure cochlea or SSC

19. Note horizontal part of facial nerve
through middle cranial fossa as
continuation of GSPN

24. facial nerve in lateral part of IAC decompression is difficult even in middle
cranial fossa. It is between two solid bones of cochlea & SSC

25. facial nerve in lateral part of IAC decompression is difficult even
in middle cranial fossa. It is between two solid bones of cochlea
& SSC

26. IAC [ Internal Auditory Canal ]
Drilling

27. IAC conical tube present in angle of
SSC crest & GSPN ( more than 50 %
dehiscent )

28. IAC conical tube present in angle of
SSC crest & GSPN ( more than 50 %
dehiscent )

29. IAC has to be drilled from medial to lateral IAC first must be opened medially & then
only tracked along the direction of IAC ( postero-laterally ) Unless you injure cochlea
basal & medial turns

30. IAC has to be drilled from medial to lateral IAC first must be
opened medially & then only tracked along the direction of IAC (
postero-laterally ) Unless you injure cochlea basal & medial turns

31. KAWASE APPROACH

32. The pit infront of cochlea & IAC is
kawase approach

33. The pit infront of cochlea & IAC is
kawase approach

34. Here I am expanding kawase approach . In few minutes I show
you COA ( cochlear aperture)

35. Here I am expanding kawase approach . In few minutes
I show you COA ( cochlear aperture)

36. Probing in middle turn

37. Observe metal probe in perisiers (
dangerous) triangle

38. Observe metal probe in perisiers (
dangerous) triangle

39. Observe metal probe in perisiers (
dangerous) triangle

40. Perisiers triangle corresponds to
labyrinthine part of facial nerve

41. So the metal probe in perisiers triangle goes to the middle turn of cochlea & exactly
corresponds to labyrinthine part of facial nerve So middle turn array of CI stimulates
labyrinthine part of facial nerve causing twitchings in post-op . Then we have to switch
off those electrodes in software programming .

42. So the metal probe in perisiers triangle goes to the middle turn of cochlea &
exactly corresponds to labyrinthine part of facial nerve So middle turn array
of CI stimulates labyrinthine part of facial nerve causing twitchings in post-op
. Then we have to switch off those electrodes in software programming .

43. So the metal probe in perisiers triangle goes to the middle turn of cochlea & exactly
corresponds to labyrinthine part of facial nerve So middle turn array of CI stimulates
labyrinthine part of facial nerve causing twitchings in post-op . Then we have to switch
off those electrodes in software programming .

44. So the metal probe in perisiers triangle goes to the middle turn of cochlea &
exactly corresponds to labyrinthine part of facial nerve So middle turn array
of CI stimulates labyrinthine part of facial nerve causing twitchings in post-op
. Then we have to switch off those electrodes in software programming .

45. So the metal probe in perisiers triangle goes to the middle turn of cochlea & exactly
corresponds to labyrinthine part of facial nerve So middle turn array of CI stimulates
labyrinthine part of facial nerve causing twitchings in post-op . Then we have to switch
off those electrodes in software programming .

46. So the metal probe in perisiers triangle goes to the middle turn of cochlea &
exactly corresponds to labyrinthine part of facial nerve So middle turn array
of CI stimulates labyrinthine part of facial nerve causing twitchings in post-op
. Then we have to switch off those electrodes in software programming .

47. So the metal probe in perisiers triangle goes to the middle turn of cochlea &
exactly corresponds to labyrinthine part of facial nerve So middle turn array
of CI stimulates labyrinthine part of facial nerve causing twitchings in post-op
. Then we have to switch off those electrodes in software programming .

48. So the metal probe in perisiers triangle goes to the middle turn of cochlea & exactly corresponds
to labyrinthine part of facial nerve So middle turn array of CI stimulates labyrinthine part of facial
nerve causing twitchings in post-op . Then we have to switch off those electrodes in software
programming .

49. So the metal probe in perisiers triangle goes to the middle turn of cochlea &
exactly corresponds to labyrinthine part of facial nerve So middle turn array
of CI stimulates labyrinthine part of facial nerve causing twitchings in post-op
. Then we have to switch off those electrodes in software programming .

50. Probing in basal turn

51. Probe in basal turn opens into basal
turn cochleostomy in middle cranial
fossa

52. Probe in basal turn opens into basal
turn cochleostomy in middle cranial
fossa

53. Probe in basal turn opens into basal
turn cochleostomy in middle cranial
fossa

54. Probe in basal turn opens into basal
turn cochleostomy in middle cranial
fossa

55. Probe in basal turn opens into basal
turn cochleostomy in middle cranial
fossa

56. Probe in basal turn opens into basal
turn cochleostomy in middle cranial
fossa

57. Probe in basal turn opens into basal
turn cochleostomy in middle cranial
fossa

58. Probe in basal turn opens into basal
turn cochleostomy in middle cranial
fossa

59. See all the turns of cochlea from
middle fossa

60. SVN & FN converge

61. Superior Vestibular nerve ( SVN ) & facial nerve separatedby bills bar , that I
drilled . Observe here SVN & FN converge . Where as IVN & cochlear nerve
diverge ……….. This convergence of SVN & FN very useful in MRI reading

62. See horizontal Septum in IAC below SVN & FN ;
I cut superior Vestibular nerve ( SVN ) & FN

63. IVN & CN diverge

64. Observe here the IVN & cochlear nerve diverge ( not so clear in
cadaver )

65. Observe here the IVN & cochlear nerve diverge ( not so clear in
cadaver )

66. Observe here the IVN & cochlear nerve diverge ( not so clear in
cadaver )

67. Observe here the IVN & cochlear nerve diverge ( not so clear in
cadaver )

68. COA [ Cochlear aperture ]

74. Observe here cochlear nerve fibres going through the cibriform
area ( entry point of modiolus ) In COA ( cochlear aperture )

77. Observe in this one COA is 2.5 to 3 mm roughtly.
If COA less than 1.5 mm it is cochlear nerve aplasia

78. Cochlear implant
after
Translabyrinthine
approach

82. PSC is deeper than LSC & SSC is deeper
than PSC

83. Intact facial canal technique of Skull base .
If you transpose grade 3 facial palsy comes .

84. Ampulla of PSC bisects vertical part of
facial nerve exactly at midpoint

85. See probe coming to Sinus tympani So while clearing Sinus tympani PSC
exposed ... becareful

86. CI after LABYRINTHECTOMY
Only two is enough for CI – one is
cochlea & another cochlear nerve –
so even in vestibular schwannoma
excision by translabyrinthine
exposure we can do CI & patient
hears

88. Bills bar between FN & SVN

91. Labyrinthectomy done to enter
Posterior cranial fossa

92. VA [ Vestibular Aqueduct ]

93. https://drive.google.com/file/d/0B7F_FcpOJCfpS2lJa3NBNkVDeV
E/view?usp=sharing

94. IAC & VA are two eyes of baby in
temporal boone

95. IAC & VA are two eyes of baby in
temporal boone

97. Endolymphatic duct & Vestibular aqueduct both are same or not ........ I have to refer .
....... but clearly there is duct from vestibule to endolymphatic sac area . If it is more
than 1.5 mm it is " dilated Vestibular aqueduct " Another 1.5mm is ........, if COA (
cochlear aperture ) less than 1.5mm it is cochlear nerve aplasia.

98. Mario sanna book mention >1.5 mm VA dilated . For mnemonic sake 1.5 mm
is there at both VA & COA . One is more & one is less respectively

99. Radiologically if the width of the Vestibular aqueduct is more than the width
of the PSC, then it is dilated. -----Satish jain sir says >2mm VA dilated in any
section .

100. In HRCT Temporal bone Vestibular aqueduct ( VA )is seen parallel
to PSC ( Posterior semi circular canal ) Here also after drilling PSC
we are seeing VA

101. anatomically also after drilling PSC we are seeing VA .... so radiologically also
both sizes same [ my mnemonic & philosophy ] ..... if VA more than PSC it is
dilated

103. Abnormal cochleas dissection photos
added later in few days
Essence of abnormal cochleas
1. IP 2 is exactly like normal cochlea
2. IP 3 - wide cochleostomy & precurved electrode
3. cochlear hypoplasia -- outcomes depends on how many number
of electrodes inserted . Minimum 10 electrodes insertion should
be there to get better outcome
4. IP 1 - lateral wall electrode
5. common cavity - lateral wall electrode
6. CHARGE - still try CI , not working then ABI.
7. michel - ABI directly
In all abnormalities see cochlear nerve aplasia .... even absent in MRI ,
do EABR & keep CI

104. Part-1 of this PPT
present at weblink
www.skullbase360.in