cochlea cadaver dissection - part 1

Cochlea Cadaver Dissection- Part 1

18-04-20178.29 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 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

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 TMThe 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 semilunaris3. 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 bar5. Vertical bar

6. Cavum anterior 7. Cavum posterior

8. Fustis9. 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 implications1) It is a outlet door of sound conduction through cochlea2) It acts as resonant chamber of sound3) Sono invertion - sound can be transported through the RWM and passing through cochlea and coming outfrom oval window gives rise to good hearing - reverse way4) It transports micromolecules to inner ear by eaither diffusion or pinocytosis5) 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 sound8) pars anterior always for sound vibration RWM vibration is evident at 1500 to 3000 hzs and at higher frequencies it vibrates irrigularly9) 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 fluidIn posterior part of RWM for better diffusion10) 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 posticus13) 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 fossula14) 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 loss18) Gentamycin trans tympanic instillation for menieres disease spreads from pars posterior of RWM to vestibule through the scala rather than diffusion through the helicotrema19) 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.

http://sci-hub.cc/10.1016/j.aanat.2005.09.006


FUSTIS & FINICULUS

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 RW10) 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

Round window types

• 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

" 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 with1 compressed cochlear capsule in caratico facial angle2 Deep hypotympanum3 long trabiculae including trabicula longa4 wide concomerata lateralis and absent concomireta medialisWide postis posticus with subcochlear tunnel5 wide sinus tympani

"PARABOLIC" round window

"PARABOLIC" round window

• Dear surgeons it is "PARABOLIC" round window in shape present 1% of cases characterised by 1 two vertical limbs longer than tegmen2 wide niche3 Third limb is formed by styloid complex4 s shaped cochlea including sub vestibular portion5 wide finiculus with high pavementum pyramidalis6 deep carotid recess7 3rd part of facial nerve is nearer to middle ear

• Surgical implications1 wide angle cochlea hence cochlear implant electrode insertion is easy2 narrow vestbular window stapes surgery is difficult3 endoscopic endomeatal f n decompression is easy in these cases4 vibroplasty is easy5 infracochlear approach to petrous apex is not possible in this type of round windows6 endoscopic endomeatal approach to IAC is easy in this type of cases7 s shaped cochlea here allows wide transcochlear approach to clivus

Inferior cochlear vein

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.

Crest of round window


Development of the bony round window niche from the 16th fetal week (A) to newborn (F). The firstossification centers of the otic capsule appear around the round window, but the inferior wall of the niche does notbegin 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 entireprenatal 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


Development of the bony round window niche from the 16th fetal week (A) to newborn (F). The firstossification centers of the otic capsule appear around the round window, but the inferior wall of the niche does notbegin 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 entireprenatal 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.



COCHLEOSTOMIES 1. INFERIOR Cochleostomy

2. ANTERO-INFERIOR Cochleostomy3. SUPERIOR Cochleostomy

4. SV[ Scala Vestibular ] Cochleostomy5. MIDDLE TURN Cochleostomy

6. APICAL TURN/SUPERIOR TURN Cochleostomy

INFERIOR Cochleostomy

INFERIOR 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

Posterior tympanotomy

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

SUPERIOR Cochleostomy

Superior cochleostomy notch

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 removed

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

Pyramid drilled

SV [ Scala Vestibular ] cochleostomy

Notch between OW & RW

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

MIDDLE TURN cochleostomy&

PARISIER'S TRIANGLE (DANGEROUS TRIANGLE)

PARISIER'S TRIANGLE (DANGEROUS TRIANGLE)

Perisier's triangle is very important triangle in endoscopic ear surgery1) 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 nerves7) 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 points1) 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 canal3) facial nerve contains 10000 axons that are responsible for the innervation of the face musculature and also for the communications with other nerves human body4) work with injured facial nerve requires lot of patience.

• RULE OF 2 IN TEMPORAL BONES1) The diameter of geniculate fossa is 2 mm2) The distance between between geniculate fossa to anterior wall of vestibule is 2 mm3) The thickness of geniculate crest is 2 mm4 ) The diameter of horizontal facial nerve in that area is 2 mmHence while drilling the bone or curetting the bone at perigeniculate area it is not advisable to use bigger burs more than 2mm diameter5) 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

Still not opened .

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

SP = subtotal petrosectomy

DRILLOUTS

1. BASAL TURN drillout 2.MIDDLE TURN drillout

3. APICAL TURN / SUPERIOR TURN drillout

BASAL 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

MIDDLE TURN drillout

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

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

Gross picture of CI drillouts

Part-2 of this PPT present at weblink https://www.slideshare.net/muralichandnallamothu/cochlea-cadaver-dissection-part-2

https://www.slideshare.net/muralichandnallamothu/cochlea-cadaver-dissection-part-2

https://www.slideshare.net/muralichandnallamothu/cochlea-cadaver-dissection-part-2

cochlea cadaver dissection - part 1

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