Middle ear

Anatomy of middle ear (development & anomalies, structures & supports,blood supply, clinical points)

1. ANATOMY OF THE MIDDLE EAR BY: DR. Pooja Sanal kumar

2. First pharyngeal pouch: Pharyngotympanic tube Middle ear cavity Mastoid antrum(dorsal expansion of cavity) First pharyngeal arch: Malleus Incus Tensor tympani muscle Ligament of malleus Second pharyngeal arch: Stapes Stapedius muscle First pharyngeal membrane -Tympanic membrane EMBRYOLOGY OF MIDDLE EAR

3. MECKEL’S CARTILAGE REICHERT’S CARTILAGE

4. Anomalies Malformed ossicles Ossicular agenesis Malleus incus fusion Ossicular mass Incudostapedial joint disarticulation Facial nerve Stapedial artery

5. Contents of middle ear 3 Ossicles 2 Muscles – tensor tympani & stapedius Chorda tympani Tympanic plexus ligaments Air

6. Communication Anteriorly: Pharyngotympanic tube nasopharynx Posteriorly: Aditusmastoid antrum

7. Divisions of middle ear Mesotympanum Hypotympanum Epitympanum

8. Walls of middle ear Lateral Medial Floor Roof Anterior Posterior

9. Lateral wall Largely by tympanic membrane Lesser extend by bony outer attic wall (SCUTUM) Chorda tympani nerve passes across-lateral to long process of incus & medial to handle of malleus.

10. Lateral wall

11. Roof of middle ear Formed by Tegmen tympani(both petrous and squamous portion of temporal bone form it) Separates tympanic cavity from middle cranial fossa. Also forms roof of aditus and antrum.

12. Floor of the middle ear Formed by thin plate of bone separates the hypotympanum from the dome of jugular bulb. Maybe congenitally deficient - jugular bulb is separated by mucosa. Tympanic branch of glossopharyngeal nerve pierces floor between jugular fossa and lower opening of carotid canal.

13. FLOOR

14. Anterior wall of middle ear Thin plate of bone separating from internal carotid artery. 2 openings: Lower-Eustachian tube Upper-Canal of Tensor tympani muscle

15. ANTERIOR WALL

16. Medial wall of middle ear Promontory Oval window (fenestra vestibuli) Sinus tympani Round window (fenestra cochleae) Facial nerve canal (above oval window) Processus cochleariformis (hook-like projection, housing tensor tympani muscle tendon) Prominence of lateral semicircular canal.

17. Posterior wall of middle ear Pyramid-bony projection; stapedius tendon appears through its submit, gets attached to neck of stapes. Aditus-opening through which attic communicates with the antrum. Fossa incudus-close to aditus, lodges short process of incus. Vertical part of facial canal behind pyramid. Posterior canaliculus- aperture for emergence of chorda tympani.

18. Facial recess Depression on posterior wall, lateral to pyramid. Shallow lower down Medially - facial nerve Laterally – chorda tympani Above – fossa incudis Posterior tympanotomy-direct access to middle ear without disturbing posterior wall.

19. OSSICLES

20. Ossicles- malleus Largest Parts-head, neck, handle, lateral and anterior processes. Head and neck in epitympanum. Handle in fibrous layer of tympanic membrane. Suspended by superior malleal ligament Lateral process receives ant and post folds from tympanic annulus Articulates with the incus-a saddle type synovial joint

21. Incus Body Two processes Short process Long process(parallel to handle of malleus) Lenticular process- articulate with head of stapes.

22. Stapes Parts Head Neck Ant and posterior crura Foot plate

23. Mastoid antrum Large air containing space Communicates with attic through aditus Roof-tegmen antri (cont. of tegmen tympani) Lateral part formed by plate of bone marked by McEwen’s triangle. Floor – openings of mastoid air cells.

24. Mastoid & its air cell system Mastoid consists of bone cortex and air cells. Develops from squamous & petrous bones Petrosquamal suture persists as bony plate korner’s septum, separating superficial squamosal and deep petrosal cells 3 types of mastoid: Well-pneumatised or cellular-well developed cells with thin intervening septa. Diploetic- mastoid with marrow spaces & few air cells. Sclerotic or acellular- no cells/marrow spaces.

25. Depending on location, mastoid cells are divided: Zygomatic Tegmen Perisinus Retrofacial Perilabyrinthine Peritubal Tip Marginal Squamosal

26. Intratympanic muscles Tensor tympani Origin-cartilaginous part of auditory tube Insertion- upper end of handle of malleus Nerve supply by- mandibular nerve Action- tenses tympanic membrane Stapedius O-pyramidal eminence I-neck of stapes N-facial n. A-tilts its footplate in oval window

27. Blood supply 6 ARTERIES Anterior tympanic branch of maxillary a.- tympanic membrane. Stylomastoid branch of posterior auricular a.- middle ear & mastoid cells Petrosal branch of middle meningeal a. Superior tympanic branch of middle meningeal a. Tympanic branch of internal carotid Branch of a. of pterygoid canal. Venous drainage: pterygoid venous plexus & superior petrosal.

28. Lymphatic drainage Retropharyngeal lymph nodes Parotid lymph nodes Upper deep cervical lymph nodes

29. Nerve supply Tympanic branch of glossopharyngeal n. -sensory to lining of middle ear, antrum & auditory tube. Superior & inferior carotico-tympanic n. - vasomotor Facial n. - Chorda tympani- taste sensation & secretomotor fibres for submandibular & sublingual glands Greater petrosal n.- secretomotor lacrimal, nasal glands N. to stapedius muscle Mandibular n.

30. Tympanic plexus nerves Tympanic branch of glossopharyngeal n. Superior & inferior carotico-tympanic n. Branch from Facial ganglion Supplies mucous membrane of middle ear, mastoid air cells & Eustachian tube.

31. clinical Otitis media- common in infants and children. Progression of URTI to middle ear through pharyngotympanic tube Complication: acute mastoiditis & mastoid abscess Meningitis & temporal lobe abscess Labyrinthitis- causing vertigo and vomiting Cerebellar abscess

32. Hyperacusis – paralysis of stapedius muscle Otosclerosis- abnormal ossification of annular ligament. (m/c cause of conductive deafness in adults)

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35. Promontory Formed by basal turn of cochlea Contains nerves forming tympanic plexus Tympanic branch of ninth nerve may be covered by bone forming a small canal

36. Oval window Behind and above the promontory. Connects tympanic cavity with the vestibule. Closed by footplate of stapes and annular ligament.

37. Round window Lies below and behind the promontory. Separates middle ear from Scala tympani. Closed by fibrous secondary tympanic membrane. Sinus tympani is a deep recess bounded by subiculum below & ponticulus above lying between round & oval window.