middle ear anatomy Dr. Nisha 1) copy.pptx

Middle ear anatomy emphasis on endoscopic structures

1. MIDDLE EAR ANATOMY Dr. Nisha Dagar

2. MIDDLE EAR CLEFT The middle ear cleft consists of the Tympanic cavity, Eustachian tube and Mastoid ai r cell system.

3. THE TYMPANIC CAVITY The tympanic cavity is a irregular, air-filled space within the temporal bone between the tympanic membrane laterally and the osseous labyrinth medially. It contains the ossicles, muscles and structures, like the tympanic segment of the facial nerve . Divided into three compartments The epitympanum (upper), The mesotympanum (middle) and Hypotympanum (lower )

4. The epitympanum or attic , lies above the level of malleolar folds and is separated from the mesotympanum and hypotympanum by a series of mucosal membranes and folds. The mesotympanum lies opposite the tympanic membrane. The h ypotympanu m lie s belo w th e l e v el o f th e in f erio r par t of the tympanic sulcus and is continuous with the mesotympanum above.

5. THE LATERAL WALL The lateral wall of the tympanic cavity is formed by the Bony lateral wall of the epitympanum superiorly, Tympanic membrane centrally and Bony lateral wall of the hypotympanum inferiorly. The lateral epitympanic wall is wedge-shaped in section and its shape . Inferior portion is also called the outer attic wall or scutum.

6. Present in the bone of the medial surface of the lateral wall of tympanic cavity - The petrotympanic fissure (also known as the squamotympanic fissure) is a fissure in the temporal bone that runs from the temporomandibular joint to the tympanic cavity. The petrotympanic fissure is 2 mm long which opens anteriorly just above the attachment of the tympanic membrane. It receives the anterior malleolar ligament and transmits the anterior tympanic branch of the maxillary artery which supplies the tympanic membrane.

7. THE ROOF The roof of the epitympanum is the tegmen tympani It is a thin bony plate that separates the middle ear space from the middle cranial fossa. It is formed by both the petrous and squamous portions of the temporal bone. The petrosquamous suture line, which does not close until adult life, can provide a route of access for infection into the extradural space in children. Veins from the tympanic cavity running to the superior petrosal sinus pass through this suture line.

8. THE FLOOR The floor of the tympanic cavity separates the hypotympanum from the dome of jugular bulb. Its thickness varies according to the height of the jugular fossa. Occasionally, the floor is deficient and the jugular bulb is then covered only by fibrous tissue and a mucous membrane. At the junction of the floor and the medial wall of the cavity there is a small opening that allows the entry of the tympanic branch of the glossopharyngeal nerve into the middle ear.

9. MEDIAL WALL Promontory Oval window Round window Tympanic part of bony facial nerve canal Lateral semicircular canal Processus cochlearformis

10. The promontory is a rounded elevation occupying much of the central portion of the medial wall. Formed by basal turn of cochlea. usually has small grooves on its surface containing the nerves which form the tympanic plexus.

11. OVAL WINDOW Close by a footplate of the stapes. It s si z e a v e r a g e 3.2 5 m m lon g and mm wide. 1.75 Lies behind and above the promontory A kidney shaped openin g that c onnects the tympanic cavity with the vestibule.

12. ROUND WINDOW Lies below and behind the oval window Separated by subiculum(post extension of promontory) Ponticulus.anothe r ridge above subiculum an d runs t o pyramid on the posterior wall Sinus tympani is where ponticulus and subiculum meet RWN is 2.3mm×1.9mm and is place d at right angle s t o plane of stapes foot plate

13. FACIAL NERVE CANAL The facial nerve canal (or Fallopian canal ) runs above the promontory and oval window in an anteroposterior direction. The facial nerve canal is marked anteriorly by the processus cochleariformis , a curved P rojection of bone, concave anteriorly, which houses the tendon of the tensor tympani muscle as it turns laterally to the handle of the malleus. The region above the level of the facial nerve canal forms the medial wall of the epitympanu m Behind the oval window, the facial canal starts to turn inferiorly as it begins its descent in the posterior wall of the tympanic cavity.

14. The dome of the lateral semicircular canal is the major feature of the posterior portion of the epitympanum, lying posterior and extending a little lateral to the facial canal

15. It has a smooth rounded lateral surface that often has microdehiscence s. When the bone is thin or the nerve exposed by disease, there are two or three straight blood vessels clearly visible along this line of nerve. These are the only straight blood vessels in the middle ear and indicate that the facial nerve is very close by . In front and a little below this, above the processus cochleariformis, may be a slight swelling corresponding to the geniculate ganglion, with the bony canal of the greater superficial petrosal nerve running for a short distance anteriorly.

16. THE POSTERIOR WALL The posterior wall is wider above than below. In upper part , a large irregular opening – the aditus ad antrum, that leads back from the posterior epitympanum into the mastoid antrum. Below the aditus is a small depression, the fossa incudis, which houses the short process of the incus and its suspensory ligament. Below the fossa incudis and medial to the opening of the chorda tympani nerve is the facial recess. The pyramid - a small hollow conical projection with its apex pointing anteriorly. This house the stapedius muscle and tendon, which inserts into the posterior aspect of the head of stapes. The canal within the pyramid curves downwards and backwards to join the descending portion of the facial nerve canal.

17. FACIAL RECESS The facial recess is a groove which lies between the pyrami d with facial nerve, and the annulus of the tympani c membrane The facial recess is bounded: Medial ly by - facial nerve Laterally - by the tympani c annulus with the chorda tympani nerve running obliquely through the wall between the two.

18. The angle between the facial nerve and the chorda allows a posterio r tympanotomy , allowing access to the middle ear from the mastoid without disruption the tympanic membrane.

19. SINUS TYMPANI Boundaries: Superior: Ponticulus Inferior: Subiculum Lateral: Mastoid Segment of Facial Nerve Medial: Posterior semicircular canal It evades direct surgical visualization during surgery. Site for cholesteatoma recurrence

20. The sinus tympani is a posterior extension of the mesotympanum and lies deep to both the promontary and the facial nerve. This extension of air cells into the posterior wall can be extensive, and is probably the most inaccessible site in the middle ear and mastoid. The sinus can extend as far as 9 mm into the mastoid bone when measured from the tip of the pyramid. The medial wall of the sinus tympani becomes continuous with the posterior portion of the tympani c cavity where it is related to the oval and round window niches and the subiculum of the promontory. On rare occasions it can communicate with the mastoid air cells.

21. Contents of middle ear cavity Air 3 ossicles : malleus, incus and stapes 2 muscles : tensor tympani & stapedius nerves : chorda tympani & tympanic plexus Mucosal folds & ligaments Blood vessels

22. THE MALLEUS Largest of the three ossicles - 9mm length It Has Head, Neck, Anterior and Lateral Process, Handle o Suspended by the superior ligament between head and the tegmen tympan i. Head has saddle - shaped facet on its posteromedial surface o to articulate with the body of the incus

23. Head Neck Anterior Process Handle Lateral Process

24. THE INCUS It has a Body, Short Process and a long process and a lenticular process body of the incus is suspended by the superior incudal ligament that is attached to the tegmen tympani. Long process extends downwards behind the handle of malleus articulates with the head of the stapes by its lenticula r process.

25. Short process - Lodges in the fossa incudis via Posterior incudsl ligament . Lenticular process - Sometimes been called the fourth ossicle because of its incomplete fusion with the tip of the long process

26. Body Short P r ocess Facet Long Process Lenticular Process

27. THE STAPES Shaped like a stirrup Consists of a head, neck, the anterior and posterior crura and a footplate. The Head points laterally and has a small cartilage- covered depression for a synovial articulation with the lenticular process of the incus

28. The foot plate directs medially and closes the Oval window. Stapedius tendon inserts into the posterior part of the neck and upper portion of the posterior crus.

29. Anterior Crus Head Neck Foot Plate Posterior Crus

30. canal MUSCLE ORIGIN INSERTION NE R VE SUPPL Y ACTION Tensor typmani Cartilaginous part of ET, its own bony Upper part of handle of malleus Branch from mandibular nerve [V 3 ] tensing tympanic membrane to reduce the force of vibrations in response to loud noises MUSCLES OF THE MIDDLE EAR Stapedius pyramidal eminence Neck of stapes Branch of facial nerve [VII] pulls the stapes posteriorly and prevents excessive oscillation in loud noises

31. THE CHORDA TYMPANI NERVE . It enters the tympanic cavity from the posterior canaliculus at the junction of the lateral and posterior walls. It runs across the medial surface of the tympanic membrane between the mucosal and fibrous layers. Then passes medial to the upper portion of the handle of the malleus above the tendon of tensor tympani .

32. The point of entry of the chorda tympani into the facial nerve bundle is usually at the level of the inferior third of the facial canal on its anterior wall. The nerve carries taste sensation from the anterior two-third of the same side of the tongue and secretomotor fibres to the submandibular gland. Continues forwards and leaves by way of the anterior canaliculus (canal of Huguier ) which subsequently joins the petrotympanic fissure.

33. THE TYMPANIC PLEXUS It is formed by the – Tympanic branch of the glossopharyngeal nerve (jacobson’s nerve) and – Caroticotympanic nerves, which arise from the sympathetic plexus around the internal carotid artery. Th e nerve s for m a plexu s o n th e promontor y an d provid e the branche s t o th e mucous membrane linin g th e tympani c cavit y , eu stachian tube and mastoid antrum and air ce lls . The plexus also provides branches to join the greater superficial petrosal nerve and the lesser superficial petrosal nerve that contains the parasympathetic fibres of the glossopharyngeal nerve.

34. Mu c osa l F old s o f th e Middl e E ar

35. Between 3 rd to 7 th month of fetal age , the mesenchymal tissue of middle ear cleft is absorbed. Simultaneously the primitive tympanic cavity develops by a growth of an endothelium-lined fluid pouch(Tubo Tympanic Recess) extending from the ET into the cleft. The terminal end of the TTR buds out to form 4 primary sacci- saccus anticus,saccus medius, saccus superior and saccus posticus The sacci or pouches start to enlarge in the middle ear cleft to replace the pre-existing mesenchyme. MUCOSAL FOLD DEVELOPMENT

36. Walls of the pouches - mucosal lining of middle ear Mucosal folds- Plane of contact between two neighbouring pouches.

37. □ Mu c osa l f old s e x t en d f r o m the wall of middle ear to its content & carry ligament s and blood vessel s to the ossicles. □ Mucosal folds- two types Composite fold : ligament+ lining mucosa ex:Ant.MLF, Lat.MLF and Post. Incudal fold Duplicate fold: fusion of two expanding air sac walls in absence of any interposing structure. ex: tensor tympani fold, lateral incudomalleal fold.

38. □ Importan t fold s i n middl e ear: Anterior malleal fold Posterior malleal fold Anterior malleal ligamental fold Lateral malleal ligamental fold Superior malleal fold Superior incudal fold Posterior incudal fold Medial incudal fold Lateral incudomalleal fold Tensor tympani fold

39. Anterior Malleal Fold Origin : anterior portion neck of malleus Insertion : anteriorly on ant. tympanic spine Forms: medial wall of ant. Pouch of Von Troltsch Posterior Malleal Fold Origin : posterior portion neck of malleus Insertion : posteriorly on post. tympanic spine Forms: medial wall of post. Pouch of Von Troltsch

40. Anterior Malleal Ligamental Fold Originates from neck of malleus & extends to the anterior attic bony wall. Reflected from lateral wal l of middle ear over Ant. Process and ligament of malleus ant part of chorda tympani . Originates from neck of malleus & extends to the anterior attic bony wall. Reflected from lateral wal l of middle ear over Ant. Process and ligament of malleus ant part of chorda tympani Low posterior part is broad and represents – ant. Limit of Prussak’s space.

41. Lateral Malleal Ligamental Fold Originates from middle portion of the neck of malleus & attaches to attic outer wall Posteriorly confluent with ant. Descending portion of Lat. IMF Mostly complete, thick fold and strong , so prevents progression of pars flaccida retraction Represents roof of Prussak’s space and the floor of the lateral malleal space

42. Superior Malleal Fold : Extends between superior surface of Malleal head and tegmen. Contains Superior Malleal ligament. Divides upper unit of attic into anterior and posterior parts. Superior Incudal Fold: Extends between superior surface incudal body to tegmen Divides posterior attic to lateral and medial part

43. d Posterior Incudal Fold Lies between the fibres of the post. incudal ligament Medial Incudal Fold Lies between the long process of the incus and the tendon of the stapedial muscle upto pyramidal eminance

44. Lateral Incudomalleal Fold Present superiorly in relation to lateral malleal ligamental fold Divides upper lateral attic space from the lower lateral attic space It has 2 extensions: Posteriorly it horizontally extends to insert medially onto body of the incus & incudomalleal joint. Laterally , it insert onto the medial surface of the bony wall of scutum

45. Ant. Portion of the this fold bends inferiorly towards the neck of malleus & merges with post. portion of lat. MLF representing the post. limit of Lat. Malleal space Level is about 1mm higher than the roof of Prussak’s space

46. Tensor Tympanic Fold Part of tympanic diaphragm Arises posteriorly from the tensor tympani tendon Anteriorly inserts into a transverse crest(supratubal ridge) of anterior wall of the attic Medially insert on the bony canal of the TTM Laterally insert on anterior malleal ligament Separates the anterior epitympanic recess superiorly from the supratubal recess inferiorly

47. TTF results from fusion of saccus anticus & anterior saccule of the saccus medius Inclinatio n angl e o f th e TT F varies bet. 80 -100 depending on the variable growth of each saccule Determines the size of Supra Tubal Recess and Anterior Epitympanic Recess

48. TTF complete -total separation between ant. epitympanum and protympanum But in majority of population TTF is incomplete. Resulting in direct communication between ET to ant. Epitympanic recess and then to posterior attic. Hence prevents attic dysventilation.

49. Tympanic Diaphragm formed by Three malleal ligamental folds The posterior incudal fold The Tensor Tympani Fold The lateral incudomalleal fold Incus and Malleus As theses components are on different level Tympanic Diaphragm is not fully Horizontal Separates the upper unit of attic superiorly and lower unit of attic, the Prussak’s space inferiorly from mesotympanum

50. Tympanic Isthmus Attic and mastoid are isolated from mesotympanum by Tympanic Diaphragm Attic aeration occurs through a 2.5 mm opening in the tympanic diaphragm - Tympanic Isthmus Anteriorly - extends from tensor tympani muscle Posterosuperiorly – post. Incudal ligament Posteroinferiorly – pyramidal eminence Medially – limited by attic bone Laterally – limited by body and short process of incus and head of malleus

51. Tympanic isthmus divided by the medial incudal fold into 2 portion The Anterior Tympanic Isthmus Between TTM anteriorly & the stapes posteriorly The Posterior tympanic Isthmus Between short process of incus & stapedial muscle

52. Clinical Correlation In long standing COM, granulation tissue and webs - block the tympanic isthmus – failure of attic ventilation even in presence of normal ET and well aerated mesotympanu m This is called selective attic dysventilation Results in chronic attic inflammation, attic retraction pockets and attic cholesteatoma Incomplete TTF allows good ventilation from the protympanic space to anterior attic and prevents attic dysventilation even in case of tympanic isthmus blockage This signifies the importance of TTF removal during surgical treatment of middle ear disease to ensure a good ventilation of the attic region

53. MIDDLE EAR SPACES anterior posterior

54. THE EPITYMPANUM (ATTIC) Situated above the imaginary line passing through the lateral process of malleus Lodges the - hea d an d nec k o f malleus - bod y an d short proces s o f incus Boundaries Lateral wall – shrapnell’s membrane (in f) - scutum (sup) Posterior wall – almost entirely by aditus ad antrum

55. i t contains latera l semicircular cana l this wall may be pneumatized b y supralabrynthine tract Medial wall - part of medial wall situated above the tympanic segment of the facial nerve & Tensor Tympani Muscle. Posterior wall : by Aditus ad antrum Inferiorly : Tympanic Diaphragm divides attic into upper unit & lower unit ( Prussak”s space)

56. UPPER UNIT OF ATTIC Above the tympanic diaphragm Medially – tympanic diaphragm separates upper unit from mesotympanum almost entirely except at tympanic isthmus Laterally – tympanic diaphragm separates the upper unit of attic from lower unit (Prussak’s space) Posteriorly – communicates with mastoid cavity through aditus

57. POSTERIOR ATTIC Contains mainly – post. part of the head of malleus . - body and short process of incus Distance from tip of incus to attic roof is 6 mm Superior Incudal fold – sagittal plane. Divides into - medial posterio r (larger) - latera l posterior attic (smaller) Medial posterior attic Also called as Medial Incudal space Medially – latera l semicircular canal an d fallopian canal Laterally – ossicles and superior Incudal fold

58. Lateral Posterior Attic Narrower Laterally – outer attic wall Medially – malleus head, incus body, superior Incudal fold Divided into 3 spaces Upper lateral attic –Superior Incudal space,lateral Malleal space and 2.Lower lateral attic – inferior Incudal space Superior Incudal space Lies in a more superior position in relation to lateral Malleal space Inferiorly – incudomalleal fold (separates from inf. Incudal space)

59. Lateral Malleal space Lies above the lateral malleal fold Medially: malleus head & neck Laterally: outer attic wall Anterior : Anterior malleal fold Posteriorly: downward turning end of incudomalleal fold * Superiorly opened to superior incudal space Lower Lateral Attic: Inferior Incudal Space Lies between short process and body of Incus medially & scutum laterally.

60. Anterior Attic or Anterior Epitympanum Anterior to the head of malleus and superior Malleal fold □ Cog – bony crest that extends inferiorly from the tegmen - superior t o cochleariform process - - anterosuperior to malleus head Divides anterior attic into 1- posterior (small) – Anterior Malleal Space 2- anterior (large) – Anterior Epitympanic Recess

61. Anterior Malleal Space Variable size Situated between head of malleus posteriorly and cog anteriorly

62. Anterior Epitympanic Recess Anterior epitympanic sinus/ Anterior epitympanic space/ sinus epitympani Superiorly – Anterior part of tegmen tympani Anteriorly – Root of zygoma Posteriorly – Cog Laterally – Scutum Medially – ant. portion of the tympanic portion of facial nerve and geniculate ganglion Floor - cochleariform process and tensor tympani fold

63. AER is highly important in cases of 1. Recurrent otorrhea with central or anterior perforation not responding to medications Middle ear effusion that persists or recurs despite repetitive myringotomies with tube insertion Anterosuperiorly oriented retraction pocket In these cases if the TTF is complete – blocks aeration of anterior epitympanum from antero- superior mesotympanum creating dysventilation syndrome These patients will not respond to posterior atticotomy alone Resection of the cog and TTF is fundamental to create ant. Route of ventilation

64. Lower unit of attic (Prussak’s space ) Formed from posterior pouch of Von Troltsch as a prolongation of Superior Saccus Boundaries Roof – lateral Malleal fold Floor – neck of malleus Anterior – anterior Malleal fold Laterally – pars flaccida and lower edge of scutum Posteriorly – opened to post. Pouch of Von Troeltsch, posterior malleal fold Ventilation route is independent of the upper unit of attic Ventilation through posterior pouch of Von Troeltsch – rough and narrow when compared to tympanic isthmus

65. Prussak’s space dysventilation and attic cholesteatoma □ COM – thick mucus secretion – closure of post. Pouch of Von Troeltsch - selective dysventilation of Prussak’s space –pars flaccida retraction pocket with adhesion to malleus neck Initially sac of the retraction pocket remains small and superficial to ossicles Continued retraction and keratin accumulation – enlargement of sac and expansion via pathways of least resistance

66. PROTYMPANUM Lies ant. to a frontal line drawn through the ant. Margin of tympanic annulus Anteriorly – Eustachian tube Posteriorly – Mesotympanum Laterally – Lateral lamina ( separates PT from mandibular fossa) Medially – cochlea posteriorly and carotid canal anteriorly Roof – bony semicanal for Tensor tympani muscle and TTF SUPRATUBAL RECESS Superior extension of protympanum Lies between superior border of tympanic orifice of ET and TTF

67. Hypotympanum Lies below a horizontal plane from inf. margin of fibrous annulus to inferior margin of cochlear promontory Five walls Anterior wall – carotid canal medially and dense bone laterally Posterior wall – inferior part of styloid complex and vertical segment of facial nerve canal (may contain retrofacial cells) Outer wall – tympanic bone Medial wall – lower part of promontory and petrous bone Inferior wall – thin bony plate separating from jugular bulb

68. RETROTYMPANUM Posterior part of tympanic cavity medial & posterior to the tympanic annulus Vertical segment of Facial Nerve & the PE divides it- The Lateral Space( Facial Recess) Medially – facial canal and pyramidal eminence Laterally – chorda tympani Superiorly – Incudal buttress Inferiorly – chordo-facial angle (18 - 30 ) Chordal ridge – divides facial recess into - Facia l sinus (superiorly) - Latera l tympani c sinus (inferiorly)

69. 2. The Medial Space Also called as the Tympanic sinus Ponticulus divides tympanic sinus to Posterior Tympanic Sinus(Superiorly ) Sinus tympani( Inferiorly)- Largest sinus of Retrotymp. In 10% population the sinus tympani and posterior tympanic sinus form one confluent recess Based on depth sinus tympani is of 3 type T ype A(Shallow) Type B(intermediate) Type C(very deep)

70. Mesotympanum Narrowest & biggest compartment Boundaries ✔ Medially – promontory ✔ Laterally – pars tensa ✔ Anteriorly – protympanum ✔ Posteriorly – retrotympanum ✔ Inferiorly – hypotympanum ✔ Superiorly – Tympanic diaphragm Acts like a channel allowing air coming from ET to pass through the Tympanic Isthmus upward to provide aeration of whole attic

71. TYMPANIC MEMBRANE POUCHES 1. Anterior pouch of Von Troeltsch Situated between Anterior Malleal fold and pars tensa Communicates with supratubal recess and protympanum 2. Posterior pouch of Von Troeltsch Situated between posterior Malleal fold and pars tensa Develops posteroinferiorly and opens in the most cranial portion of mesotympanum Main route of ventilation of Prussak’s space

72. MASTOID AIR CELLS Vary considerably in number, form & size Interconnected & lined by squamous non-ciliated epithelium Mastoid processes can be pneumatic, sclerosed or mixed Mastoid process develops by the age of 2 yrs Antrum is well developed at birth Aditus ad antrum is the opening in the posterior wall of middle ear and leads posteriorly to antrum

73. MASTOID ANTRUM The roof of mastoid antrum (tegmin antri) separate it from middle cranial fossa. The lateral: Formed by squamous temporal bone Medial wall: Related with the posterior and horizontal semicircular canal Posteriorly: communicate by several openings with mastoid air cells. – Important surgical marks to mastoid antrum is the MacEwen’s Triangle

74. MACEWEN’S TRIANGLE Superior : temporal line Anterior : postero-superior margin of bony external auditory canal opening Posterior : tangent drawn to mid-point of posterio r wall of external auditory canal Contains spine of Henle Mastoid antrum lies 12-15 mm deep to triangle

75. KORNER’S SEPTUM Membranous persistence of petrous squamous suture line in temporal bone gives illusion of mastoid antrum rather true antrum is below this septum Residual disease may be left below this septum,if not realised.

76. BLOOD SUPPLY Arteries : Middle ear i s supplied b y th e followin g 1) T wo main arteries Anterior tympanic branch of maxillary artery Stylomastoid branch of posterior auricular artery 2)Four minor arteries Petrosal branch of middle meningeal artery Superior tympanic branch of middle meningeal artery Branch of artery of pterygoid canal Tympanic branch of internal carotid Veins : Pterygoid venous plexus Superior petrosal sinus

77. LYMPHATIC DRAINAGE Middle ear : Retropharyngeal & parotid nodes ET : Retropharyngeal group of nodes

78. EUSTACHIAN TUBE 36 mm long in adults Directed anteriorly, inferiorly & medially from anterior wall of M.E., forming angle of 45 with horizontal & sagittal planes Enters naso-pharynx 1.25 cm behind posterior end of inferior turbinate . Lateral 1/3 rd is bony and medial 2/3 rd is fibrocartilagenous part. Junction b/w 2 parts is isthmus, narrowest part of Eustachian Tube.

79. Blood supply of ET: Ascending pharyngeal artery Middle meningeal artery Artery of pterygoid canal Veins drain into pterygoid venous plexus

80. THANK YOU