Cochlea cadaver dissection - part 1

Cochlea Cadaver
Dissection- Part 1
12-05-2017
2.35 pm

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Throughout our life we have to
practice temporal bone

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

Round window in
Cochlear implant

Helicotrema (at right angles to a line
between the oval and round windows)

ROUND WINDOW MEMBRANE SO FAR
NEGLECTED PART IN OTOLOGIC SURGERY
Surgeons, so far round window membrane is most
neglected part in otological surgery endoscopic
visualisation of RWM with 2.7 mm 45 degree
scope gives more information
Dear surgeons,
These are pictures of round window membrane
RWM may be kidney shaped, round or triangular
or oval or semilunar
The thickness of membrane is 60 micro mm
The length is 1.70 mm the width is 1.35 mm
It contains all three layers like TM
The entrance of niche is 2.2 mm.

Still experts opinion has to be taken regarding below line diagram -
don’t take it granted – below line diagram is in the process of
developing
1. Round window membrane
2. Crista semilunaris
3. Fibrous band
Crista semilunaris & fibrous band devides
RWM into pars anterior & pars posterior.
Floor of Round window is devided into
Horizontal bar & Vertical bar
4. Horizontal bar
5. Vertical bar
6. Cavum anterior
7. Cavum posterior
8. Fustis
9. Opurculum or Crista

1 Round window membrane 2 Crista semilunaris 3 Fustis
4 Horizontal bar 5 cavum posterior 6 Cavum anterior 7 vertical
bar 8 Pars anterior 9 Pars posterior 10 Crista

Surgical implications
1) It is a outlet door of sound conduction through cochlea
2) It acts as resonant chamber of sound
3) Sono invertion - sound can be transported through the
RWM and passing through cochlea and coming outfrom
oval window gives rise to good hearing - reverse way
4) It transports micromolecules to inner ear by eaither
diffusion or pinocytosis
5) For cochlear implant surgeons RWM is not directly
posteroior to scala tympani
So scala is present just antero superior to RWM hence
surgeon has to remove crista to insert electrode directly in
to scala tympani

• 6) Rwm is divided in to pars anterior and pars posterior by fibrous band
arising from crista semilunaris
The implant electrode shoud be introduced from pars anterior to enter
the scala if electrode is introduced from pars posterior it touches osseous
osseous spiral lamina and electrode does not go into scala.
7) The floor of niche divided by horizontal bony bar and small vertical bar
into cavum posterior and cavum anterior
These bony cavums act like resonant spaces to outlet sound
8) pars anterior always for sound vibration RWM vibration is evident at
1500 to 3000 hzs and at higher frequencies it vibrates irrigularly
9) pars posterior is always tor micromolecules diffusion in to inner ear ant
it contains more melanocytes so for gentamycin instillation it is better to
place fluid
In posterior part of RWM for better diffusion
10) Most of the round windows have false membranes hence it is better to
remove those before instillation of gentamycin.

• 11) Micro molecules of 1mue easily passes through the RWM but
micromolecules more than 3 mue can not pass through the
membrane so surgeon during instillation of intratympanic
gentamycin has to observe this point (not to add sodium bicarb in
gentamycin solution )
12) Rupture of RWM occur in pars anterior it looks like a slit with
leak into cavum anticus and cavum posticus
13) Cochlear aqueduct inner opening is present in scala tympani
just anterior to crista semilunaris still inside is opening of cochlear
vein so obstruction to cochlear vein causes sensory neural learing
loss outer opening of cochlear aqueduct is present in pyramidal
fossula
14) Fustis gives strong support to RWM unnecessory excessive
drilling of fustis in cholesteatoma surgery causes may accidentally
rwm rupture.
15) rupture of RWM is one of the causes for sudden SN loss

16)Fustis gives strong support to rwm unnecessory
excessive drilling of fustis in cholesteatoma surgery causes
may accidentally RWM rupture.
17) Rupture of RWM is one of the causes for sudden sn loss
18) Gentamycin trans tympanic instillation for menieres
disease spreads from pars posterior of RWM to vestibule
through the scala rather than diffusion through the
helicotrema
19) complete closure of round window is the good
alternative treatment in SSCS (superior semicircularcanal
fistula syndrome)
20) The second most common site of otosclerosis is round
window During stapes surgery it is better to visualise the
round window for better results

what a great great description in
paper http://sci-
hub.cc/10.1016/j.aanat.2005.09.
006
Schematic drawings showing
variations of the round window
niche in adults (right side). The
tegmen (t) andthe postis anterior
(pa) of the normal niche are
formed completely by
membranous bone while the
postis posterior (pp)and the
fundus (f) are formed by chondral
bone but covered superficially
with membranous bone. The first
two rowsdemonstrate alterations
within the entrance of the niche
and the lower row represents
structures outside the nichewhich
hide its entrance.

Relation of OSL [ = Osseus spiral
laminae ] & RW niche [ = opening ]

Anatomy of the human round window (left ear-medial view). A, The RW
is fan shaped and conical and opens into the RW niche (*). CA, cochlear
aqueduct; ST, scala tympani. B, A CI electrode array has been inserted
through the RW. The electrode rides on the crista fenestrae. – from
paper title “Is the Human Round Window Really Round? An Anatomic
Study With Surgical Implications”

FUSTIS
•
it is fustis a solid bony column connecting the retrotympanum to round
window niche. So far this structure is neglected Microscopically it may
not be clearly visible, but endoscopically it is seen clearly The surgical
implications of this structure are
1) its origin is pylogenically different from other parts of that area
hence it behaves differently
2) It contains enzymes which are resistant to cholesteatoma
destruction
3) it prevents sinus cholesteatoma extending downwards..
4) This structure is directed towards round window, in narrow round
window niche by following its upper border, we can identify the round
window membrane
5) It divides upper part of subtympanic sinus, concomerata into
medialis and lateralis. C medialis is site for posterior ampullary nerve
section.
6) Fustis regulates smooth out flow of sound waves from round
window membrane.

• 7) It helps in creation of pressure difference between round and oval windows
encourages acoustic coupling.
8) It gives support round window niche because both postis anticus and postis
posticus contains cochlea and subcochlear portion that are hollow structures.
9) This structure modulates according to round window niche i. e, "V" shaped,
square shaped, triangular gothic shaped, like that, to have a relation with RW
10) In absent sibiculum, the fustis gives support.
11) Fustis narrows the round window niche there by protects the round window
membrane (rupture)normally.
12) embryologically fustis develops between periosteal layer of the labyrinthine
capsule and the thin smooth plate of Pavementum Pyramidalis and it is
ontogenically important structure.
So surgeons, fustis is very important structure at outflow gate of sound in middle
ear.
In 1968 Bruce Proctor mentioned, Recently prof Presutti, Prof Marchioni and Prof
Joao F Nogueira described this part.
so surgeons please look this important but poor part while performing surgeries
because it is present in all middle ears..

Type A fustis. f fustis, sp styloid
proeminence, st scala tympani, rw round
window

Type B fustis. f fustis, sp styloid
proeminence, st scala tympani, rw round
window

Right ear. Endoscopic view of fustis type B. ow oval
window, st scala tympani, fu fustis, pe pyramidal
eminence, rw round window

Right ear. The tool shows the scala tympani. ow oval
window, st scala tympani, fu fustis, rw round window

A. Original round window. B. Basilar membrane. C. Osseous spiral lamina. D.
Reflection of perilymphatic fluid. E. Darker area of first curve of the basal turn
of the scala tympani. F. Blood vessels. G. Modiolus. H. Removed bone of
round window overhang.

FUSTIS position must be known for CI
surgeons

Sometimes you may not appreciate fustis by Sinus tympani
approach but for Veria technique fustis is very important.

between fustis & finiculus SCC (
subcochlear canal ) present

SCC = Sub Cochlear Canaliculus,

Between the fustis and the finiculus a subcochlear canaliculus is often seen, which is a
tunnel that connects the round window chamber with the petrous apex via a series of
pneumatized cells.
Right ear. Endoscopic anatomy of inferior retrotympanum. fu fustis, t tegmen, pp
posterior pillar, f finiculus, j jacobson’s nerve

Right ear. Endoscopic anatomy of the retrotympanum during
dissection for acustic neuroma surgery.
fu fustis, fn facial nerve, ow oval window, pr promontory, scc
subcochlear canaliculus, et Eustachian tube

Right ear. Endoscopic dissection during surgery, after drilling the
promontory. ow oval window, st scala tympani, scc subcochlear
canaliculus

Subcochlear canaliculus type A

Subcochlear canaliculus type B

Subcochlear canaliculus type C

• So far round window is neglected part in
middle ear Now a days it is gaining popularity
For type4 and 5 t plasties sono inversion
techniques viroplasties gentamycin and other
chemical perfusions cochlear implant
insertions corticosteroid perfusions in s n d
skullbase approaches round window is
important There are so many verieties of
shapes of r w s I have previously discussed 4
types of r w s

" High arched" round window
• Dear surgeons it is" High arched" round window it is
present 1-3%of cases you can compare this window to
normal r w which is shown here The arched round
window associated with
1 compressed cochlear capsule in caratico facial angle
2 Deep hypotympanum
3 long trabiculae including trabicula longa
4 wide concomerata lateralis and absent concomireta
medialis
Wide postis posticus with subcochlear tunnel
5 wide sinus tympani

"PARABOLIC" round window
• Dear surgeons it is "PARABOLIC" round
window in shape present 1% of cases
characterised by
1 two vertical limbs longer than tegmen
2 wide niche
3 Third limb is formed by styloid complex
4 s shaped cochlea including sub vestibular
portion
5 wide finiculus with high pavementum
pyramidalis
6 deep carotid recess
7 3rd part of facial nerve is nearer to middle ear

• Surgical implications
1 wide angle cochlea hence cochlear implant electrode
insertion is easy
2 narrow vestbular window stapes surgery is difficult
3 endoscopic endomeatal f n decompression is easy in
these cases
4 vibroplasty is easy
5 infracochlear approach to petrous apex is not
possible in this type of round windows
6 endoscopic endomeatal approach to IAC is easy in
this type of cases
7 s shaped cochlea here allows wide transcochlear
approach to clivus

A, Illustration showing the RWM and surrounding structures seen through the facial recess. The red box represents the
hook region of the cochlea that was modeled in this study. B, Anatomy of the round window and surrounding structures
after removing the bone from the model. C, The RWM and spiral ligament have been removed from the model, and the
scala tympani has been made transparent to show the intracochlear structures. BM, basilar membrane; CA, cochlear
aqueduct; CT, chorda tympani; DR, ductus reuniens; EAC, external auditory canal; FN, facial nerve; I, incus; ICV, inferior
cochlear vein; LSC, lateral semicircular canal; OSL, osseous spiral lamina; PSC, posterior semicircular canal; S, stapes; SL,
spiral ligament; SM, scala media; SSC, superior semicircular canal; ST, scala tympani; SV, scala vestibuli; RWM, round window
membrane.

http://sci-
hub.cc/10.1016/j.aanat.2005.
09.006
Development of the bony round
window niche from the 16th fetal
week (A) to newborn (F). The first
ossification centers of the otic capsule
appear around the round window, but
the inferior wall of the niche does not
begin to ossify until the 17th fetal
week (B). The first sign of the crest of
round window can be seen in the 18th
week
(C) and it develops rapidly up to the
23rd week (D). The walls of the niche
show intensive growth during the
entire
prenatal period but its typical
appearance is not complete until the
eighth fetal month (E). f – fustis, pa –
postis anterior, pp – postis posterior, t
– tegmen of the round window, arrow
– crest of the round window.

OPERCULUM of round window
drilled

Operculam must be drilled even to
make cochleostomy ... Cochleostomy
notch done

HOOK [ = Crista Semilunaris ] of
Round window

COCHLEOSTOMIES
1. INFERIOR Cochleostomy
2. ANTERO-INFERIOR Cochleostomy
3. SUPERIOR Cochleostomy
4. SV[ Scala Vestibular ]
Cochleostomy
5. MIDDLE TURN Cochleostomy
6. APICAL TURN/SUPERIOR TURN
Cochleostomy

Best / ideal is INFERIOR ( not antero-inferior ) cochleostomy
which is direct trajectory to scala tympani

Best / ideal is INFERIOR ( not antero-inferior ) cochleostomy
which is direct trajectory to scala tympani ..... See I stopped
about to open . Then try pick

Observe operculum drilled. Round window intact . Cochleostimy intact
....... Cochleostomy INFERIOR...... What I realized is cochleotomy
opening will not open within seconds . It takes sometime

See endoateum of cochleostomy not torn with burr ......... Upper
one round window . Lower one cochleostomy

Upper one round window . Lower one cochleostomy .......... Round window is very
simple ............. Definitely inferior cochleostomy is direct trajectory but we need to drill
more time ........ Residual hearing may damage

Two openings connected......... But drilling is more . I
fear residual hearing lost because of more drilling

Amount of drilling is somuch in
INFERIOR cochleostomy

The round window niche is visualized through the facial recess. If the round
window niche is divided into quadrants, the conchleostomy should be
performed in the anterior inferior quadrant.

First using a larger 1.5 to 2 mm bur portion of the bony promontory is removed just anterior to
the anterior/inferior annulus of the round window membrane. A 1-mm bur is then used to
expose the endosteum of scala tympani.

Yes.. Superior cochleostomy leading to Scala vestibuli & Scala tympani .
Observe partition ( osseus spiral lamina ) in superior cochleostomy……
Cochlear electrode array kink if you pass by superior cochleaostomy in
scala tympani … so Anterior inferior or INFERIOR is better

Above partition is SV [ scala vestibuli ] &
below partition is ST [ scala tympani ]

Incus & incus buttress has to be removed in rotated cochleas grade 3 & 4
before mohnish's technique of posterior canal wall reduction

Stapes dislocated ……Foot plate removed . Now i am going to make
cochleostomy in between RW & OW to enter Scala vestibuli in meningitis
cases in ossificans cases

SV [ Scala Vestibular ]
cochleostomy

Note cochleostomy between RW & OW leading to Scala vestibuli & separate from
superior cochleostomy
Note spiral lamina in superior cochleostomy

Note spiral lamina through
SV cochleostomy between OW & RW

All opening from above 1. OW 2. SV cochleostomy 3. Superior
cochleostomy 4. RW5. INFERIOR cochleostomy

All opening from above 1. OW 2. SV cochleostomy 3. Superior cochleostomy
4. RW5. INFERIOR cochleostomy

MIDDLE TURN cochleostomy
&
PARISIER'S TRIANGLE (DANGEROUS
TRIANGLE)

PARISIER'S TRIANGLE
(DANGEROUS TRIANGLE)
Perisier's triangle is very important triangle in endoscopic ear surgery
1) Superior limb is formed by inferior part of HFN
2) The apex is formed by the geniculate ganglion
3) The base is formed by the anterior commissure (end) of oval window
4) Inferior limb is formed by tunning point of jocobson's nerve to the the
geniculate ganglion.

• The surgical implications are
1) This triangle contains labyrinthine part of FN.
2) During transotic or transcochlear approaches surgeon should respect this triangle and drill carefully
to avoid injury to FN.
3) Clinically labyrinthine part consists of two segments a meatal segment of nerve, labyrinthine part of
nerve. total length of this nerve is 3 to 5 mm. Anteriorly we can see these parts clearly through this
triangle.
4) 1st part of FN passes close to lower border of precochlear HFN towards anterior end of oval window
in this triangle.
5) Irregular drilling of cochlea in this triangle damages FN That is why it is called DANGERS TRIANGLE.
6) During trans meatal endoscopic dissection of IAC, this triangle important for identification of nerves
7) Translabyrinthine approach visualises posterior surface of 1st part of FN, in transcochlear approaches
the anterior surface of the nerve is exposed. In transottic approaches 270 to 320 degrees of 1 st part of
FN is exposed.
8)Observe closely the labyrinthine part of FN there is a constriction of labyrinthine segment and meatal
segment.
Facial nerve key points
1) Facial nerve changes direction 5 times during its course from brain stem to styloid foramen.
2) No other nerve in body covers such a long distance in bony canal
3) facial nerve contains 10000 axons that are responsible for the innervation of the face musculature
and also for the communications with other nerves human body
4) work with injured facial nerve requires lot of patience.

• RULE OF 2 IN TEMPORAL BONES
1) The diameter of geniculate fossa is 2 mm
2) The distance between between geniculate fossa to anterior wall
of vestibule is 2 mm
3) The thickness of geniculate crest is 2 mm
4 ) The diameter of horizontal facial nerve in that area is 2 mm
Hence while drilling the bone or curetting the bone at
perigeniculate area it is not advisable to use bigger burs more than
2mm diameter
5) The meatal segment of facial nerve is usually 2 mm anterior and
superior to superior vestibular nerve.
My special thanks to prof Livio presuitti, prof Daniele Marchioni and
prof Jao Flavio Nogueira who taught me this Anatomy

While making middle turn cochleostomy we shouldn’t
injure the labyrinthine part of facial nerve present in
perisier’s triangle

Notch 2 to 3 mm anterior to OW & below the processes
cochleriformis leads to middle turn

For middle turn cochleostomy also we need to drill a lot . Not
opening that much easily

Now opened .
In middle & apical turns SV is more than ST ……I don't know why

See how depth the middle turn
cochleostomy

All opening from above 1. OW 2. Middle turn cochleostomy 3.
SV cochleostomy 4.Superior cochleostomy 5. RW 6.INFERIOR
cochleostomy

We have to appreciate the same labyrinthine part of facial nerve by perisiers triangle (
dangerous triangle ) also . So we shouldn't go more than 2 to 3 mm to OW while
doing middle turn cochleostomy

APICAL TURN / SUPERIOR TURN
cochleostomy

here I lifted the tensor tympani muscle & I made cochleostomy exactly in
tensor tympani groove which is superior turn cochleostomy

Labyrinthine part of facial nerve in
transmastoid approch by CWU [
Canal Wall Up ]
Labyrinthine part of facial nerve
decompression

Labyrinthine part of FN can be
decompressed by intact bridge
transmastoid approach

Labyrinthine part of facial nerve decompression…….. Observe middle cranial
fossa bone & dura also decompressed from labyrinthine part of facial nerve

This labyrinthine part of facial nerve stimulated in cochlear
implant by electrodes especially in common cavity & other
abnormal cochleas . Then we have to deactivate that electrode

CWD [ canal wall down ] + SP [
subtotal petrosectomy ]

CWD bone dust ………CWD + SP ( subtotal petrosectomy ) has to be done in
CSOM + CSF leak + abnormal cochleas

DRILLOUTS
1. BASAL TURN drillout
2.MIDDLE TURN drillout
3. APICAL TURN / SUPERIOR TURN
drillout

Without doing CWD you can't do basal turn drilling
So CWD + SP is vital in CI surgery

Note scala vestibular & superior cochleostomy leading to Scala vestibuli &
Inferior cochleostomy leading to Scala tympani

The current drilling is called apex of
basal turn

Note the drilling direction of middle turn is in the same
curvature of basal turn

Note the drilling direction of middle turn is in the same curvature of basal turn

Note the drilling direction of middle
turn is in the same curvature of basal
turn ( scala vestibuli turn )

Scale vestibuli of middle turn is more
wider than scala vestibuli of basal turn

Observe middle turn drillout meeting
superior cochleostomy

1mm cutting burr is the key for CI surgery
First time burr head broken

Chaaa.... no another 1mm cutting burr . 1mm diamond causing charring .
So we have to keep minimum three sets of 1mm & lesser size to start CI surgery .

I am amazed the human hearing frequency in middle turn &
facial associated with middle turn only .

Note horizontal part of facial nerve , tensor tympani muscle ,
middle turn drill , basal turn drill from above downwards

Note horizontal part of facial nerve , tensor tympani muscle , middle turn drill , basal
turn drill from above downwards

PERISIER’S [ DANGEROUS ]
TRIANGLE

Observe here
1. Middle turn wall associated with horizontal part of facial nerve
2. Middle turn cavity associated with labyrinthine part of facial nerve in
perisiers ( dangerous ) triangle .
So main culprit is labyrinthine part of facial nerve in post CI facial nerve
stimulation

Perisiers triangle also important in
malignancy of ear

See ... how the basal turn keeping middle turn in her lap & inturn middle turn
keeping apical turn in her lap So in HRCT in axial section in both cranial &
caudal sections you will see basal turn only .
Don't confuse that in cranial section you will see apical turn .

Perisier's triangle ( dangerous triangle ) which denotes labyrinthine
part of facial nerve …… Corresponds exactly to middle turn drillout

Perisier's triangle ( dangerous triangle ) which denotes labyrinthine part of
facial nerve…….. Corresponds exactly to middle turn drillout

APICAL TURN/ SUPERIOR TURN
drillout

Cochlea cadaver dissection - part 1

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