cochlea cadaver dissection - part 2

Cochlea Cadaver Dissection- Part 2

18-04-20178.26 pm

Part-1 of this PPT present at weblink

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http://www.skullbase360.in/

Middle cranial fossa approach for

Cochlear implant

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

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

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

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

See the probe inserted through superior cochleostomy from middle cranial fossa exactly corresponds to superior

cochleostomy just below tensor tympani from middle ear

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

tympani from middle ear

See the probe inserted through superior cochleostomy from middle cranial fossa exactly corresponds to

superior cochleostomy just below tensor tympani from middle ear

Labyrinthine part of facial nerve in middle cranial fossa

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

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

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

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

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

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

& SSC

IAC [ Internal Auditory Canal ] Drilling

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

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

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

KAWASE APPROACH

The pit infront of cochlea & IAC is kawase approach

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

Probing in middle turn

Observe metal probe in perisiers ( dangerous) triangle

Perisiers triangle corresponds to labyrinthine part of facial nerve

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 .

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 .

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 .

Probing in basal turn

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

See all the turns of cochlea from middle fossa

SVN & FN converge

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

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

IVN & CN diverge

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

COA [ Cochlear aperture ]

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

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

Cochlear implant after

Translabyrinthine approach

PSC is deeper than LSC & SSC is deeper than PSC

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

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

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

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

Bills bar between FN & SVN

Labyrinthectomy done to enter Posterior cranial fossa

VA [ Vestibular Aqueduct ]

https://drive.google.com/file/d/0B7F_FcpOJCfpS2lJa3NBNkVDeVE/view?usp=sharing



IAC & VA are two eyes of baby in temporal boone

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.

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

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 .

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

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

Abnormal cochleas dissection photos added later in few days

Essence of abnormal cochleas

1. IP 2 is exactly like normal cochlea2. IP 3 - wide cochleostomy & precurved electrode3. 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 electrode5. common cavity - lateral wall electrode6. 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

Part-1 of this PPT present at weblink

www.skullbase360.in

http://www.skullbase360.in/

cochlea cadaver dissection - part 2

Education