SURGICAL ANATOMY OF EXTERNAL AND MIDDLE EAR

1. SURGICAL ANATOMY OF EXTERNAL AND MIDDLE EAR Dr Mubeena Dr Mubeena

3. Development of external ear Outer part of first branchial cleft 6 cartilaginous tubercles appear towards the end of first fetal month 3 on first arch 3 on 2nd 20 th week – adult shape

4. Development of external auditory canal Ectoderm of first visceral cleft Funnel shaped tube Meatal plug Recanalisation of this plug forms epithelial lining of bony meatus 28th week - fully formed

5. Development of tympanic membrane Outer epithelial layer – ectoderm of visceral cleft Middle fibrous layer – mesoderm between first visceral cleft and tubotympanic recess Inner mucosal layer – endoderm from a part of recess

6. Anatomy of external ear • Elastic cartilage • Helix • Antihelix • Triangular fossa • Scaphoidfossa • Concha

7. Tragus • Antitragus • Lobule • Incisuraterminalis • Cartilage of auricle • Skin of auricle

8. Surgical importance • Cartilage from tragus, perichondrium from tragus or concha and fat from ear lobule used for reconstructive middle ear surgeries • Conchal cartilage used to correct depressed nasal bridge

9. Nerve Supply of Pinna

11. External auditory canal • Extends from concha to tympanic membrane • 24mm long • Outer 1/3rd- cartilaginous • Inner 2/3rd – bony • Direction – cartilaginous – inwards, upwards, backwards bony – inwards, downwards and forwards.

12. External auditory canal • Cartilaginous part • 8mm • Continous with cartilage of pinna • Fissures of Santorini • Skin contains ceruminous and pilosebaceous glands • Furuncles

13. External auditory canal • Bony part – 16mm • 2 constrictions - At the junction of cartilaginous and bony portion - Isthmus - 6mm lateral to tympanic membrane • Anterior recess

14. Relations of external auditory canal Superior Anterior Middle Cranial Fossa Temporomandibular joint, Superficial temporal vessels, Auriculotemporal N, Parotid Gland, Pre Auricular LN Medial Middle Ear Facial N, Parotid Gland Mastoid Posterior Inferior

15. Nerve supply of EAC • Anterior wall and roof – Auriculotemporal nerve • Posterior wall and floor– Auricular branch of vagus • Posterior wall – also fibres of facial nerve

16. Tympanic membrane • Elliptical disc • Angle of 55o with floor of meatus • Height- 10 mm • Front to back – 8 -9mm • Thickness – 0.1mm

17. Tympanic annulus which sits in tympanic sulcus • Notch of RivinusAnterior and posterior malleolar folds

18. Layers of tympanic membrane • Outer epithelial layer • Middle fibrous layer – Radial, circular and parabolic fibres • Inner mucosal layer – continous with middle ear mucosa

19. Tympanic membrane • Pars tensa • Below the malleolar folds • Has all 3 layers • Point of maximum convexity - umbo • Cone of light

20. Pars flaccida (Shrapnel’s membrane) • Triangular area above the malleolar folds • Devoid of fibrous layer

21. Nerve supply of tympanic membrane • Internally – Tympanic plexus • Externally – • Anterior half by Auriculotemporal nerve • Posterior half by Auricular branch of vagus

22. Development of middle ear

23. Development of Ossicles & Muscles • 1st arch • Malleus & Incus • Tensor Tympani • 2nd arch • Stapes • Stapedius • Ossicular development Starts by 4th week of gestation • Completed by 25 weeks

24. MIDDLE EAR CLEFT • Tympanic cavity • Eustachian tube • Mastoid antrum • Aditus • Mastoid air cells

25. Tympanic cavity • Irregular air filled space within the temporal bone • Contents • 3 ossicles: Malleus, incus and stapes • 2 muscles: Tensor tympani and stapedius • 2 nerves: Chorda tympani and tympanic plexus (IX) • Mucosal folds and ligaments • Vessels

26. Tympanic Cavity • EPITYMPANUM (ATTIC) • MESO TYMPANUM • HYPOTYMPANUM • Protympanum

27. Tympanic cavity may be thought of as a box with 4 walls, a roof and a floor

29. Roof of tympanic cavity • Tegmen Tympani - a thin plate of bone • Formed in part by petrous & part by squamous bone & Petro-squamous suture

30. Floor of Tympanic cavity • Thin plate of bone • Separates the tympanic cavity from the dome of the Jugular bulb • Structures passing – small opening for tympanic branch of Glossopharyngeal nerve

31. Anterior wall of tympanic cavity

33. Lateral Wall • Part membranous & Part bony • Tympanic membrane forms the central portion • Above & below – bony outer lateral walls of epitympanum & hypotympanum

34. Medial Wall Separates the middle ear from the inner ear • Promontory – basal turn of cochlea • Oval window – opens into vestibule • Round Window – opens into scala tympani • Horizontal tympanic portion of facial nerve • Horizontal semicircular canal – above the facial nerve • Processuscochleariformis – Tendon of tensor tympani takes a turn here

37. Posterior wall • Opening to mastoid antrum • Pyramid • Facial recess (suprapyramidal recess) • Sinus tympani ( infrapyramidal recess)

39. Endoscopic view of posterior medial wall of tympanic cavity

40. Facial recess (suprapyramidal recess)

42. Auditory ossicles • Conduction of sound waves from the external ear to middle ear • Links the tympanic membrane to oval window and cochlea

43. Malleus ( Hammer) • Largest of the three • Head • Neck • Anterior process – ant malleolar ligament • Lateral Process – receives anterior & posterior malleolar folds • Handle – between fibrous & mucosal layers of TM

44. Incus (anvil) • Has a body & 2 processes • Body- epitympanum • Short process lies in fossa incudis • Long process has a small medially directed lenticular process which articulates with the stapes

45. Stapes (stirrup) • Consists of a head, neck & crura • Head articulates with incus • Stapediusisertion into posterior part of neck and posterior crura • The 2 crura join the footplate

47. Muscles • Tensor tympani 1st arch muscle Supplied by mandibular nerve Attached to neck of malleus, tenses TM • Stapedius Supplied by facial nerve Attached to neck of stapes. Dampens loud sounds

49. Nerves • Chorda tympani • Tympanic plexus • Formed by tympanic branch of glossopharyngeal nerve and caroticotympanic nerves • Supplies medial surface of TM, tympanic cavity, ET and mastoid air cells • Also carries secrotomotorfibres to parotid