anatomy & embryology ext ear & middle ear

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ANATOMY & EMBRYOLOGY OF THE EXTERNAL & MIDDLE EAR

Dr. Mohammed Shafeeq

EAR: External Ear

Middle Ear

Internal Ear (Labyrinth)

Embryology External Ear

develops around the first branchial arch

AURICLE:

Around 6th week of IUL

Developed from a series of small cartilaginous tubercles around 1st pharyngeal groove -'Hillocks' or 'Tubercles of His'

First Pharyngeal Arch1) Tragus

Second Pharyngeal Arch2) Crus of helix3) Helix4) Anti helix5) Anti tragus6) Ear lobule

Anomalies of Auricle (Pinna):

1) Preauricular sinus2) Anotia3) Bat ear deformity

EXTERNAL ACOUSTIC CANAL:

Develops from surface ectoderm covering the dorsal end of 1st pharyngeal groove

Meatus deepens by proliferation of its ectoderm

Anteriorly placed bud of epithelial cells expand vertically to form the skin which will cover the future TM

Clumps of cells then opens up as a slit to form the canal lumen and produce the pars tensa and deep external canal epithelium

Anomalies of EAC:

1) Atresia 2) Changes in curvature of canal3) Stenosis

Tympanic Membrane:

1) Inner mucosal layer from ENDODERM2) Middle fibrous layer from MESODERM3) Outer epithelial layer from ECTODERM

MIDDLE EAR - Embryology

1st pharyngeal develops by 3rd week of IULof which,

- proximal narrow part forms Eustachian Tube

- distal dilated part forms tubotympanic recess, later to Middle Ear Cleft

- in later fetal life, diverticulum appears from tubotympanic recess forming the Mastoid Antrum

OSSICLES:

- Anson in 1959

- from 1st and 2nd arch cartilages- 1st arch (Meckel's) cartilage: head of malleus & body of incus

- 2nd arch (Reichert's) cartilage: handle of malleus, long process of incus, crurae of stapes

- Otic capsule: foot plate of Stapes

Middle Ear Spaces & Folds:

numerous spaces and folds are formed when mucous membrane of tubotympanic recess encircle the ossicles.

Attic Compartment:

- Anterior Compartment- PosteriorCompartment

Compartments of Mesotympanum:

- Anterior Malleolar Fold- Posterior Malleolar Fold- Tensor Tympani Fold

Prussak's Space:

- potential space which may first to involve during extension of Cholesteatoma,

- bounded by,laterally, Shrapnell's membranemedially, Neck of Malleussuperiorly, fibres of lateral malleolar foldinferiorly, lateral process of malleus

ANATOMY External Ear

Auricle / Pinna

External Acoustic Canal

Tympanic Membrane

Auricle (Pinna)

- elastic fibrocartilage, two surfaces: medial & lateral surface

- Lateral surface characteristic prominences and depressions

- Helix most prominent outer part

- Anti Helix fold in front of helix

- Concha in front of anti-helix, hollow space divided by crus of helix - Cymba conchae & Cavum conchae

- Tragus cartilaginous projection anterior to Cavum concha

- Scaphoid fossa 'boat shaped' space b/w upper part of helix & anti helix

- Incisura Terminalis space b/w crus of helix and tragus

Cartilage avascular, derives nutrients from perihondrium

Trauma 'Boxer's Ear'

Two ligaments - Anterior Ligament- Posterior Ligament

Muscles- Extrinsic Muscles- Auricularis Anterior - Auricularis Posterior- Auricularis Superior

- Intrinsic Muscles

Blood Supply- Posterior Auricular Artery- Anterior Auricular branches of Superficial Temporal A- Superior Auricular Artery

Nerve Supply- Greater Auricular N- Lesser Occipital N- Auriculotemporal N- Auricular branch of Vagus N (Arnold's N)- fibres from Facial N

External Auditory Canal: - from concha of auricle to TM- 2.4cm long, two parts outer Cartilaginous and inner Bony part

Cartilaginous Part:- outer 1/3 of EAC, 8mm- two deficiencies 'Fissures of Santorim'

Bony Part:- inner 2/3 of EAC, 16mm- Isthmus- Anterior Recess- Foramen of Huscke- Tympanic Sulcus

Tympanic Membrane:- medial end of EAC, partition b/w EAC and middle ear- obliquely set, forming an angle of 55 degree- 9-10mm tall, 8-9mm wide and 0.1mm thick

Two parts:- Pars Tensa - Pars Flaccida ( Shrapnel's Membrane )

Three layers:- Outer Epithelial Layer- Middle Fibrous Layer- Inner Mucosal Layer

Pars Tensa:- Annulus Tympanicus- Umbo- four quadrants- 'cone of light'

Pars Flaccida (Shrapnel's Membrane):- Anterior mallelolar fold- Posterior malleolar fold

Nerve Supply:- Auriculotemporal N (Ant half of lat surface)- Auricular Br of Vagus N (Post half of lat surface)- Tympanic br of CN IX Jacobson's N (med surface)

ANATOMY Middle Ear

Middle Ear Cleft Middle ear(Tympanic cavity), Aditus, Antrum, Mastoid air cells

Middle Ear/Tympanic cavity: irregular, air filled space within the temporal bone b/w TM laterally and osseous labyrinth medially.

Contains auditory ossicles, intratympanic muscles

Middle Ear: 3 compartments

- epitympanum (attic) : lies above level of malleolar fold

- hypotympanum :lies below level of tympanic sulcus

- mesotypmanum :lies opposite pars tensa

6 surfaces Roof, Floor, Medial, Lateral, Anterior, Posterior

Roof Tegmen tympani

Floor thin plate of bone seperating hypotympanum from dome of jugular bulb

Anterior wall thin plate of bone seperates from Internal Carotid A. Two openings lower one for Eustachian tube, upper for canal of tensor tympani

Posterior wall lie close to mastoid air cells, and has following structures:- Aditus- Fossa Incudis- Pyramid- Facial Recess

Lateral wall - - TM- Scutum

Medial wall separates tympanic cavity from middle ear- Promontory- Oval window- Round window- Subiculum- Ponticulus- Canal for facial N- Processus cochleaformis- Sinus tympani

Mastoid Antrum: Air containing space in upper part of mastoid and communicates with attic through aditus- Roof: tegmen antri- Lateral wall: plate of bone on an avg 1.5cm thick in adults

MacEwen's (suprameatal) triangle: bounded by- temporal line- posterosuperior segment of bony EAC- line drawn tangent to external canal

Aditus:

- opening through which attic communicates with antrum. - Bony prominence of horizontal canal medially,- fossa incudis laterally- Facial N course below aditus

Contents of Tympanic Cavity: - Ossicles Malleus, Incus, Stapes - Intratympanic muscles Tensor tympani, Stapedius- Chorda tympani,

- Tympanic plexus

Ossicles of middle ear- MALLEUS: head, neck, handle(manubrium), lateral and anterior process

Head and neck of malleus lie in attic.

Manubrium lies embedded in fibrous layer of TM

Lateral process forms a projection and attaches to ant. & post. malleolar folds

- INCUS:- body, short process, long process

- body and short process lies in attic

- long process hangs vertically & attaches to head of stapes

- STAPES: - head, neck, Ant. & Post. Crura, Footplate

- footplate is held in oval window by annular ligament

INTRATYMPANIC MUSCLES:

Tensor tympani -

- attaches to neck of malleus- tenses tympanic membrane- derived from 1st arch- supplied by branch of Mandibular N

Stapedius -

- attaches to neck of stapes- helps to dampen loud sound, preventing noise trauma to inner ear- derived from 2nd arch- supplied by branch of Facial N

Tympanic Plexus:

- lies in the promontory

- formed by:- tympanic br of gloosopharyngeal N- sympathetic fibres from plexus around ICA

- supplies innervation to:- medial surface of TM, tympanic cavity, mastoid air cells & bony eustachian tube- carries secretomotor fibres for the parotid gland

Chorda tympani N:

- Br of Facial N enters the middle ear through posterior canaliculus

- runs on medial surface of TM b/w HOM and long process of incus

- carries taste sensation from Ant. 2/3rd of tongue

- secretomotor fibres to submaxillary and sublingual salivary glands

Blood Supply of Middle Ear:

Anterior tympanic br of Maxillary A- supplies TM

Stylomastoid br of Post Auricular A- supplies middle ear and mastoid air cells

Minor vessels:Petrosal br of middle meningeal A

Sup tympanic br of middle meningeal A

Branch of Artery of pterygoid canal

Tympanic br of ICA

Veins:drain into pteryoid venous plexus & Superior petrosal veins

Thank You....