3. 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.
4. 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
5. 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
6. 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
7. 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
8. 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
9. • 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.
10. • 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
11. 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
12. 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
4. Horizontal bar
5. Vertical bar
6. Cavum anterior
7. Cavum posterior
8. Fustis
9. Opurculum or Crista
24. 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.
25. • 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..
26.
27.
28.
29.
30. Type A fustis. f fustis, sp styloid
proeminence, st scala tympani, rw round
window
31. Type B fustis. f fustis, sp styloid
proeminence, st scala tympani, rw round
window
32. Right ear. Endoscopic view of fustis type B. ow oval
window, st scala tympani, fu fustis, pe pyramidal
eminence, rw round window
33. Right ear. The tool shows the scala tympani. ow oval
window, st scala tympani, fu fustis, rw round window
34. 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.
36. 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
37. 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
38. Right ear. Endoscopic dissection during surgery, after drilling the
promontory. ow oval window, st scala tympani, scc subcochlear
canaliculus
43. • 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
45. " 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
49. "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
50. • 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
57. 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.
58. • 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.
59. • 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
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64.
65. While making middle turn cochleostomy we shouldn’t
injure the labyrinthine part of facial nerve present in
perisier’s triangle
66. Notch 2 to 3 mm anterior to OW & below the processes
cochleriformis leads to middle turn
67.
68. For middle turn cochleostomy also we need to drill a lot . Not
opening that much easily
