Anatomy of middle ear

ANATOMY OF middle EAR

1. MIDDLE EAR AND ITS CONTENTS

2. Overview Middle ear cleft Walls of middle ear Contents of middle ear Blood supply of middle ear

3. The middle ear cleft includes the tympanum (middle ear cavity proper), the Eustachian tube, and the mastoid air cell system . Middle ear cleft:

4. The tympanic cavity is an air filled irregular space contained within the temporal bone. three auditory ossicles ( malleus , incus and stapes) with their attached muscles, chorda typani nerve,tympanic plexus, blood vessels Whole cleft lined by respiratory epithelium {ciliated columnar epithelium } , in the eustachian tube and antero inferior part of tympanic cavity Above and behind this level is pavement epithelium.

5. Middle ear cavity lies between external and inner ear. Has form of biconcave disc, measures Vertical diameter- 15mm Antero-posterior diameter- 13mm Transverse diameter-very narrow - 6mm upper part 2mm center 4mm lower part Measurements:

6. 6mm 4mm 2mm 15mm

7. . For the purpose of description the tympanic cavity may be considered as a box with six walls. The corners of this hypothetical box is not sharp.

8. Walls and its contents

9. partly Bony and membranous. Bony part: Squamous part of temporal bone : BONY LATERAL WALL OF THE EPITYMPANUM : CENTRALLY BY TYMPANIC MEMBRANE : BONY LATERAL WALL OF HYPOTYMPANUM Accordingly cavity is divided into three parts- Laterl wall:

10. . 3 parts: Epitympanum /attic : Situated above the malleolar folds of tympanic membrane i.e.,medial to horizontal part of squamous part of temporal bone above tympanic membrane. It contains the head of malleus, incudomalleolar joint and body and short process of incus. Lined by the pavement epithelium

11. Mesotympanum : situated medial to the pars tensa of tympanic membrane. Anterior mesotympanum is lined by columnar ciliated epithelium, posterior by pavement epithelium . Hypotympanum : situated below the level of tympanic membrane. Lined by ciliated columnar epithelium.

12. provides communication between antrum and rest of tympanic cavity. Superior border of attic is tegmen tympani, which is a thin wall, at times dehiscent. Divided into medial and lateral parts , by head of malleus and body of incus. Medial larger than lateral. Attic/ Epitympanum

13. Medial attic communicates with mesotympanum through opening called isthmus tympani Isthmus tympani is a narrow , elongated space divided by long process of incus into anterior isthmus with tendon of tensor tympani as anterior border. Posterior isthmus bounded by pyramidal eminence and buttress at fossa incudis .

14. Lateral attic located between the outer attic wall { scutum } - laterally . Malleus head and body incus - medially. Smaller due to two reasons- Outward projection of ossicles . Scutum runs obliquely medially from tegmen tympani to the upper edge of bony annulus.

15. The lateral epitympanic wall is wedge shaped and is directed laterally. Its lower part is called the “ scutum ” or the outer attic wall. { EASILY ERODED BY CHOLESTEATOMA }

16. Scutum : forms part of the superior deep portion of the external meatus gives attachment to the pars flaccida , which is the lateral wall of the Prussak’s space. first bony structure to be eroded by attic cholesteatoma secondary to a retraction pocket leaving a tell tale sign on HRCT temporal bone.

17. Openings in medial surface of lateral wall Posterior canaliculus for chorda tympani. Petrotympanic / Glaserian fissure Canal of Huguier

18. Posterior canaliculus : Chorda tympani Branch of facial nerve . origin may vary Enters tympanic cavity from posterior canaliculus at junction of lateral and posterior walls Runs across medial surface of TM . Passes medial to upper portion of handle of malleus above tendon of TT Leave by anterior canaliculus (canal of Huguier ) Supplies taste sensation to anterior 2/3 rd of tongue and secretomotor fibres to submandibular gland This canal also contains a branch from the stylomastoid artery

19. Petrotympanic ( Glaserian ) fissure : Opens anteriorly Slit measuring about 2mm receives the anterior malleal ligament and transmits anterior tympanic branch of maxillary artery Canal of Huguier : It lies medial to the Glaserian fissure. The chorda tympani nerve leaves through this.

20. Elliptical disc stretched obliquely. Convex towards tympanic cavity Maximum convexity is called umbo Longest diameter: 9-10mm- thickness 0.1mm Makes an angle of 55 o with the floor of the meatus. Parts: Pars flaccida and Pars tensa Tympanic membrane:

21. The greater part formed by pars tensa , wh thickened peripherally into fibrocartilagenous annulus which fits into grooved tympanic sulcus , ring like groove in the tympanic ring. The tympanic ring is deficient superiorly - 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

22. Layers: Outer epithelial Middle fibrous-in pars tensa -radial and circular fibers but not much in pars flaccida Inner mucosal Two folds arises from the notch of rivinus to the lat surface of malleus known as ant & post malleolar folds

23. Inner surface of the tympanic membrane: The TM is supplied by a vascular circle formed by the anterior tympanic artery branch from IMA 2.Posterior tympanic artery from the stylomastoid branch of the posterior auricular artery. . Blood supply of tympanic membrane:

24. 3.Tubal twig from ascending pharyngeal anastomosis 4.Arteria nutrica malleo-incudei twig from middle meningeal artery- sharpnells membrane Outer surface of the tympanic membrane: 1. Arteria manubrii having uncertain origin. 2. eep auricular artery

25. The membrane receives its innervations from the auriculotemporal branch of the (CN V) , and the auricular branch of the vagus (CN X) arnolds nerve/ aldermans nerve. Venous drainage external jugular Transverse sinus Dural veins Nerve supply of tympanic membrane:

26. Tegmen tympani. Formed by petrous part & squamous part of temporal bone and petrosquamous suture line. Transmits venous drainage into superior petrosal sinus. SEPERATES MIDDLE EAR FROM MIDDLE CRANIAL FOSSA. { PETROSQUAMOUS SUTURE LINE IN CHILDREN IS NOT COMPLETELY CLOSED SO FORMS A ROUTE FOR INFECTION TO SPREAD INTO EXTRADURAL SPACE } Roof:

27. Thin bone separating it from jugular bulb. Entirely formed by the petrous part . It is thin in newborns and thickens with age. May be deficient in some patients. The inferior tympanic canaliculus , which transmits the Jacobson’s nerve Floor:

28. Anterior Roof Floor Posterior

29. Narrow- medial and lateral walls converge Divided into upper and lower portion Lower portion : -Thin bone separating middle ear cavity from carotid artery. Perforated by superior and inferior carotico tympanic nerves, it is through these nerves sympathetic nerves reach tympanic plexus. Upper portion : Two tunnels: Lower tunnel transmits bony portion of Eustachian tube. Upper tunnel transmits tensor tympani muscle (semi tunnel). UPPER THIRD HAS ANTERIOR EPITYMPANIC SINUS WHICH IS PEUMATISED. { RESIDUAL CHOLESTEATOMA IN CANALWALL UP SURGERY } Anterior wall:

30. Named by B artolomeus E ustachius Channel which connects middle ear with nasopharynx . 36mm long. Lateral 1/3 is bony Medial 2/3 is cartilagenous Isthmus : Narrowest part of ET b/w bony and cartilagenous - 0.5MM Eustachian tube

31. Lenght12 mm , Laterally opens into anterior wall of tympanic membrane. 5X2mm ,Oval shaped,widest part of ET. Runs b/w tympanic plate and petrous part of temporal bone. RELATIONS : Superiorly – Bony roof seperating from tensor tympani Medially - Carotid canal Takes descending diagonal course at angle of 40 degree from horizontal ET BONY PART

32. CARTILAGINOUS PART : 24MM Made up of fibrocartilagenous skeleton and muscles. Passess downward froward and medially toward nasopharyngeal orifice making angle of 160 degree with bony part. J shaped . On cross section-Shepherds crook ,cartilage confined to upper and medial part. FIXED TO SKULL BASE THROUGH A GROOVE WHICH IS PRESENT B/W PETROUS PART OF TEMPORAL BONE AND GREATER WING OF SPHENOID . ET CARTILAGINOUS PART

33. PHARYNEAL END : Vertically slit like , 1-1.25 CM behind below posterior end of inferior turbinate. TORUS TUBARIS : Cartilagenous part of pharyngeal opening is raised to form a elevation. FOSSA OF ROSENMULLER :pharyngeal recess behind torus.

34. TENSOR PALATI :arises from Scaphoid fossa Spine of sphenoid Along whole length of tubal cartilage It decends ,converges and turns medially around the pterygoid hamulus and spread into soft palate. Aka DILATOR TUBE muscle – help in opening ET . Normally ET is closed –opened by swallowing and yawing by action of tensor palati and sphincter of nasopharyngeal isthmus Supplied by MANDIBULAR NERVE . MUSCLES OF ET

35. LEVATOR PALATI ; Arise from the base of petrous bone and passes under the floor of tube, inserted directly into soft palate and meets its fellow of opposite side PHARYNGEAL PLEXUS . MUCOSA OF ET : Cartilaginous part- Respiratory ciliated columnar epithelium with goblet cells . Bony part- the cilia n goblet cells decrease in number

36. The medial wall separates the middle ear from the inner ear. 1.Promontory 2.Oval window 3.Round window niche 4.Facial nerve canal 5.processus cochleariformis Medial wall

37. The most prominent portion. Rounded projection occupying most of central portion of the medial wall . Projection is by the underlying basal turn of the cochlea . The promontory has numerous small grooves on its surface. These grooves contain the tympanic plexus of nerves 1.Promontory

38. 2.Oval window ( fenestra vestibuli ). Divides medial wall into 2 parts: The inferior part is opposite the deep orifice of the external auditory canal and is directly explorable through this canal The superior part is opposite the bony lateral wall of the tympanic cavity.

39. Behind and above the promontory is the oval window. Kidney shaped opening connecting the tympanic cavity with the vestibule . Closed by stapes foot plate and its annular ligament. The long axis of the fenestra vestibuli is horizontal . 3.25mm long and 1.75 mm wide. Above this is the canal for facial nerve (horizontal portion) and below lies the promontory. Oval window ctn d ….

40. Found in a triangular niche with anterior, posterosuperior and posteroinferior border. Covered by secondary tympanic membrane The secondary tympanic membrane appears to be divided into an anterior and posterior portions by the presence of a transverse thickening It is made up of three layers; the outer mucosal, middle fibrous and an inner endothelial layer. 3.Fenestra cochlea: Round window

41. The membrane of the fenestra cochleae does not lie at the end of the scala tympani but forms part of its floor. The round window faces inferiorly and a little posteriorly, lying completely under the cover of the promontory and hence usually is difficult to visualise . Measures 2.3×1.9 mm and is placed right angle to the oval window Round window ctn d ….

42. The ampulla of the PSCC is the closest vestibular structure to this membrane. The nerve supplying the ampulla of the PSCC (singular nerve) lies close to this membrane . Hence forms a landmark for the singular nerve. This is useful during surgical procedures like singular neurectomy for treatment of intractable vertigo. Round window ctnd ….

43. Facial nerve canal , also called fallopain canal Runs above promontory and oval window in anterosuperior direction Smooth rounded lateral surface has microdehiscenses Along the line of nerve two or three blood vessels are visible(straight) This canal is marked anteriorly by processus cochleariformis and behind by the oval window 4.Fallopian canal

44. facial canal which runs above the promontary & oval window . FACIAL CANAL

45. A bony projection . Tensor tympani tendon passess through it as it turns laterally . Above the processus cochleariformis there is a small bulge in facial canal which marks the geniculate ganglion greater suprficial petrosal nerve runs in a bony canal. 5.Processus cochleariformis

46. The posterior wall can be divided into two distinct parts: The upper third-corresponds to the aditus ad antrum ;represents the posterior limit of the epitympanum The lower two thirds - correspond to the posterior wall of the retrotympanum . Posterior wall:

47. The pyramidal eminence The pyramidal eminence is situated at the center of the posterior wall immediately behind the oval window; it is about 2 mm height. It lodges the body of 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.. Posterior wall eminences:

48. The styloid eminence The styloid eminence or Politzer eminence is a recognized smoothed elevation at the inferior part of the posterior wall; it represents the base of the styloid process.

49. chordal ridge of Proctor The chordal ridge runs laterally and transversally from the pyramidal eminence to fuse with the chordal eminence. pyramidal ridge The pyramidal ridge is very prominent. It runs inferiorly from the base of the pyramidal eminence to the styloid eminence. It could be absent. styloid ridge The styloid ridge connects the styloid prominence to the chordal eminence. ponticulus subiculum Posterior wall ridges:

50. Aditus : aditus ad antrum connects middle ear space with mastoid antrum . Dimension 4 × 4 × 4 mm Fossa incudis : lodges short process of incus and posterior ligament. Pyramid : contains stapedius muscle. Recess : Facial recess Sinus tympani Posterior wall:

51. Facial recess ( suprapyramidal recess): lies lateral to facial nerve. MEDIALLY : FACIAL NERVE LATERALLY : TYMPANIC ANNULAS CHORDA TYMPANI RUNS B/W THESE. Sinus tympani ( infrapyramidal recess): the niche of two labyrinthine windows communicate posteriorly with this deep recess RELATIONS SUPERIORLY : PONTICULUS INFERIORLY : SUBICULUM LATERAL : MASTOID SEGMENT OF FACIAL NERVE MEDIAL : POSTERIOR SEMICIRCULAR CANAL { CHOLESTEATOMA NIDUS CAN BE HERE CAUSING RECCURANCe

52. Three bones : Auditory ossicles derive names from the Blacksmiths forge Malleus Incus Stapes Two muscles: Tensor tympani Stapedius Two nerves: Tympanic plexus Chorda tympani Contents of middle ear:

53. Hammer shaped ,largest -9mm 20-25mg wt 1 ST Arch derivative PARTS – Head neck anterior and lateral process, handle or manubrium. HEAD – saddle shaped facet on posteriormedial surface which articulates with body of incus. Lies in attic region Malleus (hammer)

54. This articular surface is constricted near its middle dividing the articular facet into a larger superior and a smaller inferior portions. The inferior portion of the articular facet lies at right angles to that of the superior portion. This projecting lower portion is also known as the cog or spur of the malleus. LATERAL PROCESS :important landmark in tympanic membrane ,receive anterior and posterior folds

55. The neck is narrow and flattened portion. Medial surface gives attachment to the tensor tympani Chorda tympani crosses its medial surface above the tensor thmpani tendon but below neck { SO AMPUTATION OF HEAD DOESN’T AFFECT CHORDA TYMPANI OR TENSOR TYMPANI } Handle directed medially and posteriorly to form the umbo . Anterior and lateral process. Attachments: The anterior suspensory ligament The lateral suspensory ligament The superior suspensory ligament The anterior malleal ligament The posterior malleal ligament

56. S ML TT TEN D ON

57. 1 ST ARCH DERIVATIVE resembles bicuspid tooth Measures 6 6 mm weighs about 30 mg. It has a trapezoidal body with short process, long process, and a rounded lenticular process. Both body and short process are in attic. The lenticular process connects the long process with the head of stapes. Incus (anvil):

58. Ligaments of the Incus : The posterior incudal ligament The superior incudal ligament.

59. 1 ST BONE TO UNDER GO EROSION LONG PROCESS due to precarious blood supply. BODY is in epitympanum suspended by superior incudal ligament from tegmen tympani. SHORT PROCESS : Projects backwards from the body to lie in the fossa incudis in posterior wall by short suspensory ligament.

60. Smallest ossicle Stirrup shaped 2 ND ARCH DERIVATIVE PARTS : HEAD , NECK , ANTERIOR AND POSTERIOR CRURA AND FOOTPLATE. HEAD : points laterally and has a cartilage covered area facet for articulation with lenticular process of incus. The tendon of stapedius muscle is attached to the posterior part neck of stapes and posterior part of posterior crura . Stapes (stirrup):

61. CRURA : arises from lower part of neck anterior is thinner and less curved than posterior both are hollow on concave surface, both crura join foot plate which cover oval window. FOOTPLATE : Superior margin is convex and inferior margin is straight lies over the oval window by annular ligament. Measure 3.25X1.75MM

62. INCUDOMALLEOLAR JOINT – SADDLE JOINT. INCUDOSTAPEDIAL JOINT – BALL & SOCKET JOINT. Joints in mi dd le ear:

63. Muscle in mi dd le ear Stapedius : Origin from walls of the conical cavity within the pyramid . A slender tendon emerges from the apex of the pyramid. Insertion over the post part of neck and upper portion of post crus Supplied by small branch of facial nerve

64. On contraction this muscle rocks the stapes backwards holding it firm against the annular ligament preventing excessive transmission of sound into the inner ear. Patients with facial nerve palsy have hyperacusis because of lack of action of this muscle.

65. Tensor tympani muscle Origin :wall of bony canal above eustachain tube, greater wing of sphenoid Passes backward into tympanic cavity,along medial wall little below facial nerve Enters processus cochlearformis , turns at right angles inserting into the medial aspect of the upper end of the handle of the malleus Supplied by mandibular nerve via branch from medial pterygoid nerve

66. This muscle tenses the tympanic membrane by holding the handle of the malleus thus helping the middle ear in better sound perception.

67. Chorda Tympani: Chorda tympani. Branch of facial nerve. Origin may vary. Enters tympanic cavity from the posterior canaliculus at junction of lateral and posterior wall Runs across medial surface of TM Passes medial to upper portion of handle of malleus above tendon of Tensor tympani. Leave by way of anterior canaliculus (canal of Huguier ) Supplies taste sensation to anterior 2/3 rd of tongue and secretomotor fibres to submandibular gland.

68. Tympanic plexus Over promontory Formed by Tympanic branch of 9 th nerve,also called Jacobson’s nerve Caroticotympanic nerves{ supplies the sympathetic component. } Supplies mucous membrane lining tympanic cavity ,ET and mastoid antrum and cells Also provide branches to greater and lesser superficial petrosal nerves

69. 1.ANTERIOR TYMPANIC : Branch of maxillary artery supplies : TM , Malleus,incus,anterior part of tympanic cavity. 2.STYLOMASTOID : Branch of posterior auricular artery : Stapedius muscle,posterior part of tympanic membrane. 3.MASTOID : branch of Stylomastoid artery : Mastoid air cells 4.PETROSAL : branch of middle meningeal artery : Roof of mastoid ,roof of epitympanum BLOOD SUPPLY OF TYMPANIC CAVITY

70. 5.SUPERIOR TYMPANIC : middle meningeal artery : malleus , incus , tensor tympani 6.INFERIOR TYMPANIC : ascending pharyngeal artery : mesotympanum 7.BRANCH FROM ARTERY OF PTERYGOID CANAL : meso n hypotympanum . 8.TYMPANIC ARCHES FROM INTERNAL CAROTID : meso n hypotmpanum

71. Blood supply

72. Communicates with middle ear via the aditus . Antrum is well defined at birth. Measurements: Volume: 1ml Antero-posterior diameter: 14mm Vertical diameter: 9mm Transverse diameter: 7mm Mastoid antrum :

73. Medial wall: Posterior semicircular canal and more deeply to posterior cranial fossa and endolymphatic sac Roof: Middle cranial fossa Posterior wall: sigmoid sinus Lateral wall: Thickness at birth 2mm, adult life 12-15mm, corresponds to suprameatal / Macewen’s triangle. Floor: digatric muscle laterally and sigmoid sinus medially. Mucosa : Flatenned nonciliated epithelium without goblet cells or mucous glands. Relations:

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