Round window

Round window

1. Round window 9 -2-2017 00 .09 a m

2. 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.

3. 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

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. 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

8. 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 .

9. 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

10. 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

11. 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

12. FUSTIS

13. 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. 

14. 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..

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

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

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

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

19. SCC = Sub Cochlear Canaliculus ,

20. 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

21. 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

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

23. Subcochlear canaliculus type A

24. Subcochlear canaliculus type B

25. Subcochlear canaliculus type C

26. Round window

27.  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

28. " High arched" round window

29. " 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

30. "PARABOLIC" round window

31. "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

32. 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