ANATOMY OF THE MIDDLE EAR

BY:DR. POOJA SANAL KUMAR

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

MECKEL’S CARTILAGE

REICHERT’S CARTILAGE

Anomalies

Malformed ossicles Ossicular agenesis Malleus incus fusion Ossicular mass

Incudostapedial joint disarticulation Facial nerve Stapedial artery

Contents of middle ear

3 Ossicles 2 Muscles – tensor tympani & stapedius Chorda tympani Tympanic plexus ligaments Air

Communication Anteriorly:

Pharyngotympanic tube nasopharynx

Posteriorly: Aditusmastoid antrum

Divisions of middle ear

• Mesotympanum

• Hypotympanum

• Epitympanum

Walls of middle ear

Lateral Medial Floor Roof Anterior Posterior

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.

Lateral wall

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.

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.

FLOOR

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

ANTERIOR WALL

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.

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.

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.

OSSICLES

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

Incus Body Two processes

Short process Long process(parallel to handle of

malleus) Lenticular process- articulate with

head of stapes.

Stapes

Parts Head Neck Ant and posterior crura Foot plate

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.

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.

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

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

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.

Lymphatic drainage

Retropharyngeal lymph nodes Parotid lymph nodes Upper deep cervical lymph nodes

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.

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.

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

Hyperacusis – paralysis of stapedius muscle Otosclerosis- abnormal ossification of annular

ligament. (m/c cause of conductive deafness in adults)

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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

Oval window

Behind and above the promontory.

Connects tympanic cavity with the vestibule.

Closed by footplate of stapes and annular ligament.

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.