Middle Ear Anatomy.pptx

Middle ear anatomy

1. DR VAIDEHI VADODARIYA 1 st year DNB resident ENT Anatomy of middle ear

2. The middle ear cavity is an irregular air- filled space Hollowed out in the center of the temporal bone between the external auditory meatus laterally and the inner ear medially. The middle ear together with the eustachian tube, aditus , antrum and mastoid air cells is called middle ear cleft. It is lined by mucous membrane and filled with air.

3. The middle ear is divided into: ( i ) mesotympanum (lying opposite the pars tensa ) (ii) epitympanum or the attic (lying above the pars tensa but medial to Shrapnell’s membrane and the bony lateral attic wall) (iii) hypotympanum (lying below the level of pars tensa ) The portion of middle ear around the tympanic orifice of the eustachian tube is sometimes called Protympanum . It contains the ossicles , muscles and structures, like the tympanic segment of the facial nerve.

4. Because of the convexity of the medial and lateral walls, the middle ear cavity is constricted at its center . The width of the middle ear cavity is :- 2 mm at the center 6 mm superiorly in the attic 4 mm inferiorly in the hypotympanum . In the sagittal plane, the middle ear measures about 15 mm both in the vertical and horizontal

5. Middle ear walls 4 walls with roof and floor

6. lateral wall Formed by Tympanic membrane bony tympanic ring the attic outer wall.

7. The Attic Outer Wall The attic outer wall, part of the squamous bone. It is a wedge shape plate of bone that separates the attic from the zygomatic mastoid cells laterally The scutum is a thin sharp bony spur formed by the junction of the attic outer wall and the superior wall of the external auditory canal. The scutum gives attachment to the pars flaccida of the tympanic membrane which is the lateral wall of the Prussak’s space

8. Clinical Impact The scutum is the first bony structure to be eroded by an attic cholesteatoma secondary to a retraction pocket of the pars flaccida into the attic.

9. The Tympanic Ring The tympanic ring is the most medial portion of the tympanic bone. It is C shaped In the inner aspect of the tympanic ring, there is a gutter, the tympanic sulcus , which houses the annulus of the tympanic membrane. The tympanic ring is deficient superiorly to form the notch of Rivinus . The pars flaccida inserts directly on this notch, and due to the absence of sulcus and the tympanic ring, the pars flaccida is lax rendering it more predisposed to a retraction.

10. The Tympanic Spines At the junction of the tympanic ring and the attic outer wall, we can identify two spines – The anterior and the posterior tympanic spines: 1. Anterior tympanic spine : is present at the anterosuperior end of the tympanic ring and represents the anterior limit of the notch of Rivinus 2. Posterior tympanic spine : is present at the posterosuperior end of the tympanic ring and represents the posterior limit of the notch of Rivinus

11. Anterior and posterior tympanic spines. Notice the direct insertion of the tympanic membrane on the scutum ( s ) and the absence of annulus in this zone.

12. Tympanic Canaliculi The medial surface of the tympanic ring near the tympanic spines presents three openings The Petrotympanic Fissure( Glaserian Fissure ) The petrotympanic ( Glaserian ) fissure opens anteriorly just above the attachment of tympanic membrane. It receives the anterior malleal ligament and transmits the anterior tympanic artery, a branch of the internal maxillary artery to the tympanic cavity. The Iter Chordæ Anterius ( Canal of Huguier ) The canal of Huguier is a separate canaliculus placed in the medial end of the petrotympanic fissure Through it the chorda tympani nerve leaves the tympanic cavity towards the infratemporal fossa . The Iter Chordæ Posterius Situated medial to the posterior tympanic spine. It leads into a minute canal through which the chorda tympani nerve exits to enter the tympanic cavity.

13. The Tympanic Sulcus The average depth of the sulcus is ab out 1mm. It is maximal at 6 o’clock and decreases gradually as it goes up towards the tympanic spines. Clinical Implications These changes in the depth of the sulcus reflect the stability of the insertion of the annulus In the posterosuperior quadrant the annulus is not totally inserted into the sulcus and is merely supported. This weak insertion of the posterosuperior quadrant of tympanic membrane to the tympanic ring makes it lax and predisposed to retraction.

14. The Tympanic Membrane The Tympanic membrane (TM) separates the external auditory meatus from the middle ear. It is approximately 8 mm wide, 9–10 mm high and 0.1 mm thick. The inferior part of the membrane lies more medially than the superior part. The TM forms an inclination of about 55° relative to the inferior wall of the auditory meatus The handle of the malleus is firmly attached to the central part of the inner surface of the TM and draws it centrally. This zone of the TM is called the umbo

15. The Tympanic Membrane Shrapnell divided the TM into two parts, an upper small part called pars flaccida and a lower bigger part called the pars tensa . The pars tensa , the largest part of the TM, is taut, thickened peripherally into the annulus which is inserted into the tympanic sulcus . The pars flaccida is lax, occupies the notch of Rivinus , and is attached to the scutum .

16. The Tympanic Annulus The tympanic annulus also known as Gerlach’s ligament horseshoe-like fi brocartilaginous structure that maintains the insertion of the tympanic membrane in the tympanic sulcus . The annulus is absent superiorly at the level of the notch of Rivinus . The diameter of the annulus is not uniform. The maximal mean caliber of the annulus is at 6 o’clock level. From this point, the annulus gradually thins out in both directions

17. CLINICAL APPLICATION . >Pars flaccida retraction pockets -weakest part of TM. -unorganized fibres in lamina propria . -direct insertion of the skin of the pars flaccida on the scutum in the absence of the combination annulus- sulcus. >Pars tensa retraction pockets -more common in posterosuperior part. -more vascularised . - middle fibrous layer lacks well developed circular fibrous layer. - shallow sulcus Ossicular overcrowding (poor ventilation)

18. Inferior wall The floor of the middle ear cavity is narrow. It consists of a thin plate of bone that separates the middle ear from the jugular bulb posteriorly and the internal carotid artery anteriorly . Between the artery and the jugular bulb near the medial wall, a small canal, the inferior tympanic canaliculus transmits the Jacobson’s nerve and the inferior tympanic artery.

19. The surface of this wall show irregularities due to the overlying pneumatized cells. In posterior part of the floor is the root of the styloid process which gives rise to a bony eminence, the styloid eminence.

20. JUGULAR BULB : Connects sigmoid sinus to internal jugular vein. Jugular bulb lies in posterior and largest compartment of jugular foramen. Dome lies at the floor below the labyrinth and medial to the mastoid segment of the facial nerve. Distance from Jugular bulb to posterior SCC 0-10 mm. From bulb to facial nerve laterally 0-12mm

21. SURGICAL APPLICATION Retrofacial approach to the middle ear -Drilling the area between facial nerve laterally, jugular bulb inferiorly and medially and posterior scc superiorly. - Provide access to hypo tympanum area without transposing the facial nerve. - But could not be done easily in high jugular bulb cases (dome riding above the tympanic annulus) Sagittal oblique reconstruction of a computed tomography showing- the retrofacial hypotympanotomy approach ( red arrow ). Mastoid segment of the VII nerve ( arrowheads ), hypotympanic air cells ( black arrows ), round window membrane (between the white arrows ), basal turn of the cochlea ( empty arrow ). A antrum, JB jugular bulb

22. Clinical Application Jugular Bulb Anomalies A high jugular bulb (HJB) is a condition in which the jugular bulb dome rides above the tympanic annulus. A HJB has an intact sigmoid plate which separates it from the middle ear cavity. If the sigmoid plate is deficient, the bulb protrudes into the middle ear cavity; this situation is called a dehiscent jugular bulb (JBD)

23. A HJB or JBD manifests as a pulsatile tinnitus and appears like a posteroinferior retrotympanic blue mass on otoscopic examination. Injury of a JBD during tympanomeatal flap elevation results in profuse bleeding. The incidence of high JB ranges from 5 to 20 % and that of JBD ranges from 1 to 10 % [ 17 ] .

24. Posterior Wall Highest wall about 14mm. Formed essentially by the petrous bone. Divided in 2 parts Upper third part : Aditus ad antrum connects epitympanum to mastoid antrum posteriorly . Lower two third part : Houses the vertical segment of facial nerve. The two parts are separated by the incudal buttress, a compact bone that runs from the tympanic ring laterally to the lateral semicircular canal medially. It houses the incudal fossa in its superior surface which lodges the short process of the incus .

25. The Upper Part: The Aditus Ad Antrum The aditus ad antrum connects the epitympanum of the middle ear to the mastoid antrum posteriorly . The aditus is of a triangular shape with dimensions of 4 × 4 × 4 mm height, length, and width

26. The Lower Part: The Posterior Wall of the Tympanum The posterior wall of the tympanum is a complete bony wall and bridges the bony annulus tympanicus to the bony labyrinth. It houses the vertical segment of the facial nerve. This wall presents three eminences directed anteriorly , five bony ridges, and four sinuses delimiting the retrotympanum spaces

27. medial view showing the posterior wall composed of an inferior closed part separating the middle ear from the mastoid and a superior open part, the aditus ad antrum , which connects the middle ear to the mastoid. Notice that the floor of the aditus houses the fossa incudis ( FI ), which lodges the short process of the incus

28. Posterior Wall Eminences The posterior wall presents three bony eminences: The pyramidal, chordal , and styloid eminences. • The pyramidal eminence The pyramidal eminence is situated at the center of the posterior wall immediately behind the oval window. It lodges the stapedial muscle and its apex gives passage to the stapedial tendon. The pyramidal eminence communicates with the facial bony canal by a minute aperture which transmits the stapedial branch of the facial nerve . • The chordal eminence The chordal eminence is situated lateral to the pyramidal eminence and 1 mm medial to the tympanic membrane. • The styloid eminence The styloid eminence or Politzer eminence is a recognized smoothed elevation at the inferior part of the posterior wall.

29. 1.chordal ridge of Proctor The chordal ridge runs laterally and transversally from the pyramidal eminence to fuse with the chordal eminence. 2. pyramidal ridge The pyramidal ridge is very prominent. It runs inferiorly from the base of the pyramidal eminence to the styloid eminence.. 3. styloid ridge The styloid ridge connects the styloid prominence to the chordal eminence. 4. ponticulus The ponticulus is a central structure in the retrotympanum . It is a bony ridge extending from the pyramidal process to the promontory. 5. subiculum The subiculum is a smooth bony projection that is situated posterior to the promontory and extends inferiorly from the posterior lip of the round window niche towards the styloid eminence. Therefore , it intervenes between the sinus tympani superiorly and the round window inferiorly .

30. Wall has 3 eminences, 5 bony ridges and 4 sinuses.

31. Superior wall (the tegmen ) Tegmen above ET is tegmen tubari , above tympanic cavity is tegmen tympani and over mastoid is tegmen antri . Cog is a hard and dense bony crest situated 1-2mm anterior to malleus head heading vertically towards processus cochleariformis

32. anterior wall (carotid wall) Formed entirely from the petrous bone. Separates middle ear cavity from petrous carotid artery canal. Lower Portion : - largest. anterior wall of hypotympanum . seperates from vertical segment of petrous carotid A. -2 tiny openings transmitting superior and inferior caroticotympanic nerve. 2. Middle Portion : - corresponds to protympanum Upper one for Tensor tympani muscle. Lower one for bony part of Eustachian tube. Upper Portion : -corresponds to root of zygoma which represents the anterior wall of epitympanum

33. CAROTID ARTERY AND THE ANTERIOR WALL : Carotid artery enters the temporal bone through carotid foramen. It ascends vertically in the anterior wall of hypo tympanum and in the medial wall of the bony Eustachian tube at the area just beneath the cochlea (the vertical segment); then it turns anteromedially at almost a right angle towards the petrous apex, forming the horizontal segment anteroinferiorly to the cochlea

34. Medial wall ( cochlear wall) Separates ME cleft from inner ear. Canal of TT muscle anteriorly and tympanic fallopian canal posteriorly divide it into upper third part and lower two third part. Upper third forms medial wall of epitympanum and limited posteriorly by LSCC. Lower two thirds forms medial wall of mesotympanum and has promontory on centre, oval window posterosuperiorly and round window posteroinferiorly .

35. Cochleariform Process : Anterosuperior to oval window and just inferior to tympanic segment of facial nerve. Bony canal of TT muscle ends here and tendon of muscle housed by its concave portion turns laterally and attaches at medial aspect of handle of malleus.

36. The cochleariform process is a highly important anatomical and surgical landmark to identify the facial nerve and the oval window in invasive pathologies .

37. 2. Facial nerve canal : Prominence in upper part of medial wall of mesotympanum. Runs obliquely in an anteroposterior direction from above the cochleariformis process anteriorly down below and medial to the dome of LSCC. In the medial wall the bony canal of VII could be dehiscent to leave the VII only covered with a submucosa or even prolapsing lying over the oval window

38. 3.Cochlear Promontry : Occupy most of the central portion of medial wall lodging between oval and round windows. Represents underlying basal turn of cochlea. The basal turn of the human cochlea is a bony canal.The lower half of the basal turn of the cochlea can be approached from the facial recess or external auditory canal during cochlear implantation. Transversal computed tomography of a right ear. The medial wall of the middle ear in relation to ( a ) the basal turn of the cochlea ( arrowheads ). ( b ) The second turn of the cochlea ( black arrows ), the tensor tympani muscle (arrowhead) the cochleariform process( white arrow)

39. 4. Oval window niche : Located on the posterior part of mesotympanum. Behind and above the promontory and inferior to facial nerve canal. Limited anteriorly and superiorly by CP and posteriorly by ponticulus, ST and PE. Kidney shaped opening leading to vestibule. Oval window measures 3.25mm long and 1.75mm wide. Fissula ante fenestram -> it is a strip of periotic connective tissue extending from the vestibule just anterior to the oval window through an irregular sl it -like space in the bony otic capsule to join the mucoperiosteum of the tympanic cavity below the pulley of the tensor tympani muscle.

40. 6. Round window : Niche is located in posteroinferior aspect of promontory. 2mm from the inferior margin of oval window and is separated from promontory by subiculum. Niche is usually triangular in shape having anterior, posterosuperior and posteroinferioir walls. Posterosuperior and posteroinferior wall meet posteriorly leading to sinus tympani.

41. Anterior and posteroinferior margin overlies a crest ( crista fenestra), it must be drilled away in CI surgery to insure a good exposure to allow the electrode to pass tangentially along the basal turn of cochlea. Large hypotympanic cells border the niche inferiorly and must not be mistaken for niche especially during CI.

42. ROUND WINDOW MEMBRANE: 1.35mm horizontal diameter and 1.79mm vertical. Thickness is 40-60 microns. It releases mechanical energy to the inner ear fluids associated with movement of stapedial footplate.

43. Clinical Application Passage through the membrane is possible for small molecules by passive diffusion and for larger molecules probably by endocytosis The round window membrane acts as the main gateway for local therapy of inner ear diseases. Drugs (such as dexamethasone and gentamicin ) or bacterial exotoxins (in case of acute and chronic otitis media) present in the middle ear may pass through the round window membrane to reach the inner ear

44. EAR OSSICLES Malleus

45. Incus

46. Stapes a)3.5 mm high and 1.4 mm wide. b) In horizontal plane between lenticular process of incus and oval window and below facial nerve canal.

47. MIDDLE EAR COMPARTMENTS

48. Protympanum Lies anterior to frontal plane drawn through the anterior margin of tympanic annulus. Lateral wall is thin plate of tympanic bone which separates it from mandibular fossa laterally. Medial wall consists of cochlea posteriorly and carotid canal anteriorly . Roof is composed of the bony canal for the tensor tympani muscle and the tensor tympani fold separating the protympanum from the anterior attic.

49. HYPOTYMPANUM Below a horizontal plane starting from the inferior margi n of the fibrous annulus to the inferior margin of cochlear promontory . Anterior wall : Carotid canal medially and a dense bone laterally. Posterior wall : Formed by the inferior part of the styloid complex and the vertical segment of the facial nerve canal. Outer wall: Formed by the tympanic bone. Medial wall: Formed by the lower part of the promontory and a part of the petrous bone . Inferior wall : Corresponds to a thin bony plate separati n g the hypotympanum from the jugular bulb.

50. RETROTYMPANUM It consists of several separate spaces lying in the posterior aspect of the tympanic cavity It is the site of highest incidence of middle ear pathologies especially retraction pockets and cholesteatoma. It includes four spaces: - T wo spaces lie medial to the vertical segment of the facial nerve and the pyramidal eminence . T wo spaces lie lateral to them.

51. Facial Recess The lateral spaces form the facial recess. The facial recess is bordered medially by the facial canal and the pyramidal eminence and laterally by the chorda tympani. Superiorly, the facial recess is bounded by the incudal buttress, bony boundary of the incudal fossa , which lodges the short process of the incus . Inferiorly limited by chordofacial angle. The chordal ridge which runs between the pyramidal eminence and the chordal eminence, divides the facial recess into -facial sinus superiorly -lateral tympanic sinus inferiorly

52. Facial recess serves as a posterior window to reach the middle ear from mastoid cavity, this is known as transmastoid posterior tympanotomy by drilling the posterior wall of facial recess between CT laterally and facial nerve medially. In cases of narrow facial recess, extended posterior tympanotomy is done. CTN is sacrificed and drilling is done between annulus and facial nerve. Mean width of extended facial recess is 5mm.

53. The Medial Spaces They are called the tympanic sinus , are the depressions in the posterior wall of the middle ear lie between the facial nerve and pyramidal eminence laterally and the labyrinth medially. The ponticulus , which runs from the promontory to the pyramidal eminence divides it into two spaces: The posterior tympanic sinus superiorly The sinus tympani inferiorly .

54. Sinus tympani is divided into 3 types based on its depth . Type A : Shallow and does not reach the level of vertical portion of facial nerve posteriorly. Type B : Intermediate depth and lies medial to the vertical portion of facial nerve but does not extend posteriorly deeper than the level of the facial nerve. Type C : Very deep. Extends posteriorly deeper than th facial nerve. This type cant be explored through middle ear, therefore trans mastoid retro facial approach is used which requires at least a distance of 2mm between facial nerve and PSCC to avoid injury.

55. EPITYMPANUM (ATTIC) Lateral wall of the attic is formed inferiorly by Shrapnell’s membrane and superiorly by a bony wall, called the outer attic wall. Medial wall of the attic is a part of the medial wall situated above the tympanic segment of the facial nerve and tensor tympani muscle. It contains the lateral semicircular canal. Posterior wall is occupied almost entirely by the aditus ad antrum . Inferiorly , the tympanic diaphragm divides the attic into an upper unit and a lower unit.

56. Anterior epitympanic recess in chronic otitis media: In cases of recurrent otorrhea with central or anterior perforation. Not responding to medical therapy, recurring despite repetitive myringotomies with tube insertion. TTF is complete and blocks the aeration of anterior epitympanum and anterosuperior mesotympanum creating a Dysventilation syndrome

57. Lower unit of the attic ( Prussak’s space) The Prussak’s space is situated inferior to the tympanic diaphragm The roof is the lateral malleal fold which is a low portion of the tympanic diaphragm. The floor is formed by the neck of the malleus . The anterior limit is the anterior malleal fold. The lateral wall is formed by the pars flaccida and the lower edge of the outer attic wall, the scutum . The posterior wall is opened to the posterior pouch of von Tröltsch and then to the mesotympanum . Prussak’s space is ventilated through the posterior pouch of von Tröltsch .

58. Prussak’s space dysventilation and Attic cholesteatoma : Possibility of closure of posterior pouch of von troltsch following thick mucous secretion formation during chronic inflammatory otitis is high. Selective dysventilation of the space causes development of pars flaccida retraction pocket with adhesion to the malleus neck.

59. Suratubal recess It is the superior extension of protympanum . Corresponds to the space lying between superior border of tympanic orifice of ET and Tensor Tympani Fold. It lies below anterior attic from which it is separated by TTF. The size of supratubal recess depends on anatomy of TTF. For instance, a horizontal TTF results in small or absent STR and a vertical TTF gives place to a large STR.

60. MESOTYMPANUM: The mesotympanum acts like a channel, allowing air coming from the Eustachian tube, to pass through the tympanic isthmus upward to provide aeration of the whole attic. Limited medially by the promontory and laterally by the pars tensa of the tympanic membrane. Superiorly it is separated from the attic by the tympanic diaphragm

61. 1) Tympanic membrane compartments: Anterior pouch of von Tröltsch: This pouch is situated between the anterior malleal fold and the pars tensa of the eardrum; it communicates with the supratubal recess and the protympanum Posterior pouch of von Tröltsch : This pouch is situated between the posterior malleal fold and the pars tensa of the eardrum. It is the main route of ventilation of the Prussak’s space.

62. 1. TENSOR TYMPANI MUSCLE Origin : cartilage of ET, walls of its enveloping bony canal, and adjacent portion of greater wing of sphenoid. Most medial fibres of tendon attach to cochleariform process and then turn laterally in cavity. Insertion : medial surface of the junction of neck and manubrium of malleus . Nerve supply – by trigeminal nerve via nerve to medial pterygoid. Function – draw the manubrium medially, thus tensing the TM and damping the movements of ossicular ch ain MIDDLE EAR MUSCLES

63. 2 . STAPEDIUS MUSCLE Smallest skeletal muscle in body . Origin : pyramidal eminence . Insertion : head or posterior crus of stapes. Nerve supply – stapedial branch of facial nerve. Function – contraction provokes a tilting of stapes which stretches the annular ligament, thus fixing the footplate and damping its movement. It protects the inner ear from damage caused by loud noise. lack of action of this muscle – Hyperacusis

64. Middle ear receives innervation vi a - facial nerve - glossopharyngeal nerve - sympathetic carotid plexus 1Facial nerve branches – Nerve to stapedius MIDDLE EAR NERVES 2 . Tympanic plexus - Formed by tympanic/ Jacobson’s nerve ( parasympathetic fibres) and two or three filaments from carotid plexus (sympathetic fibres). This plexus overlies promontary and gives off : - The lesser petrosal nerve - Branches to tympanic cavity mucosa

65. MIDDLE EAR VESSELS

66. MIDDLE EAR MUCOSAL FOLDS Pass from the walls of the middle ear to its contents and carry ligaments and blood vessels to the ossicles .

67. Posterior Tympano-malleal fold : - Arises from the posterior portion of the neck of the malleus. - It inserts posteriorly on the posterior tympanic spine. -medial wall of the posterior pouch of von Tröltsch. -medial edge envelops the poster ir portion of the chorda tympani. 2 ) Anterior Tympano-malleal fold : - arises from the anterior portion of the neck of the malleus and inserts anteriorly on the anterior tympanic sp ine -It forms the medial wall of the anterior pouch of von Tröltsch 3) Anterior malleal ligamental fold: It originates from the neck of the malleus and extends to the anterior attic bony wall. Its low posterior part is broad and represents the anterior limit of Prussak’s space

68. 4) Lateral malleal ligament fold : starts from the middle portion of the neck of the malleus to develop a fanlike spread before attaching to the attic outer wall . This fold is usually complete; it represents the roof of the Prussak’s space and the floor of the lateral malleal space. 5) Superior malleal fold : Lies between the superior surface of the malleus head and the tegmen in a transversal plane. Divides the attic into anterior and posterior parts. 6) Lateral incudomalleal fold: A part of the tympanic diaphragm. It lies superiorly in relation to the lateral malleal ligamental fold and separates the upper lateral attic space from the lower lateral attic space.

69. 7) Medial Incudal fold: Located between the long process of the incus and the tendon of the stapedial muscle as far as the pyramidal eminence . 8) Superior Incudal fold: Runs from the superior surface of the incudal body to the tegmen . It divides the posterior attic into lateral and medial attic. 9) Posterior Incudal fold: Runs between the fibers of the posterior incudal ligament. 10) Tensor Tympani Fold: It arises posteriorly from the tensor tympani tendon. It runs anteriorly towards the anterior wall of the attic inserting into a transverse crest. Medially it inserts on the bony canal of the TTM and laterally on the anterior malleal ligament. It separates the anterior epitympanic recess superiorly from the supratubal recess inferiorly.

70. TYMPANIC DIAPHRAGM: the complete tympanic diaphragm is made up of the three malleal ligamental folds (anterior, lateral, and posterior), the posterior incudal fold, the TTF, the lateral incudomalleal fold, and the incus and the malleus . It separates the upper unit of the attic superiorly from the mesotympanum and the lower unit of the attic, the Prussak’s space, inferiorly.

71. TYMPANIC ISTHMUS : The attic and the mastoid are isolated from the mesotympanum by the tympanic diaphragm. Attic aeration occurs through a 2.5- mm opening in the tympanic diaphragm called the tympanic isthmus. The tympanic isthmus extends from the tensor tympani muscle anteriorly to the posterior incudal ligament posterosuperiorly and the pyramidal eminence posteroinferiorly . The tympanic isthmus is limited medially by the attic bone and laterally by the body and short process of the incus and the head of the malleus .

72. Superior view of a right middle ear showing the tympanic diaphragm and the tympanic isthmus. The tympanic isthmus could be divided into anterior and posterior isthmus by the medial incudal fold ( MIF ). The green arrows represent the normal route of attic aeration from the mesotympanum .

73. Long standing COM may lead to blockage of this and it may lead to failure of attic ventilation even in the presence of normal ET and aerated mesotympanum . This is known as Selective attic dysventilation and may lead to chronic attic inflammation, attical retraction pockets and attic cholesteatoma. Incomplete TTF allows good ventilation from the protympanic space to the anterior attic and prevents attic dysventilation In case of tympanic isthmuss blockage. This confirms the importance of TTF removal during surgical treatment of middle ear diseases to e nsure a good ventilation of the attic region.

74. Thank you