SURGICAL ANATOMY OF DR MUBEENA EXTERNAL AND MIDDLE

SURGICAL ANATOMY OF DR MUBEENA EXTERNAL AND MIDDLE EAR Dr Mubeena

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 2 nd • 20 th week – adult shape

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 • 28 th week - fully formed

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

ANATOMY OF EXTERNAL EAR • • • Elastic cartilage Helix Antihelix Triangular fossa Scaphoid fossa Concha

• • • Tragus Antitragus Lobule Incisura terminalis Cartilage of auricle Skin of auricle

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

NERVE SUPPLY OF PINNA Nerve Derivation Region supplied Greater Auricular Cervical plexus C 2, 3 Medial surface and posterior portion of lateral surface Lesser Occipital Cervical plexus C 2, 3 Superior portion of medial surface Auricular Vagus X Concha and Antihelix Some supply medial surface (eminetia concha) Auriculotemporal Vc mandibular Tragus, crus of helix and adjacent helix Facial VII Probably supplies small region in the root of concha

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

EXTERNAL AUDITORY CANAL • Cartilaginous part • 8 mm • Continous with cartilage of pinna • Fissures of Santorini • Skin contains ceruminous and pilosebaceous glands • Furuncles

EXTERNAL AUDITORY CANAL • Bony part – 16 mm • 2 constrictions - At the junction of cartilaginous and bony portion - Isthmus - 6 mm lateral to tympanic membrane • Anterior recess

RELATIONS OF EXTERNAL AUDITORY CANAL Middle Cranial Fossa Middle Ear Mastoid Facial N, Parotid Gland Temporomandibular joint, Superficial temporal vessels, Auriculotemporal N, Parotid Gland, Pre Auricular LN

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

TYMPANIC MEMBRANE • Elliptical disc • Angle of 55 o with floor of meatus • Height- 10 mm • Front to back – 8 9 mm • Thickness – 0. 1 mm

• Tympanic annulus which sits in tympanic sulcus • Notch of Rivinus Anterior and posterior malleolar folds

LAYERS OF TYMPANIC MEMBRANE • Outer epithelial layer • Middle fibrous layer – Radial, circular and parabolic fibres • Inner mucosal layer – continous with middle ear mucosa

TYMPANIC MEMBRANE • Pars tensa • Below the malleolar folds • Has all 3 layers • Point of maximum convexity - umbo • Cone of light

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

NERVE SUPPLY OF TYMPANIC MEMBRANE • • Internally – Tympanic plexus Externally – Anterior half by Auriculotemporal nerve Posterior half by Auricular branch of vagus

DEVELOPMENT OF MIDDLE EAR

DEVELOPMENT OF OSSICLES & MUSCLES • 1 st arch • Malleus & Incus • Tensor Tympani • 2 nd arch • Stapes • Stapedius • Ossicular development Starts by 4 th week of gestation • Completed by 25 weeks

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

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

TYMPANIC CAVITY • EPITYMPANUM (ATTIC) • MESO TYMPANUM • HYPOTYMPANUM • Protympanum

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

ROOF OF TYMPANIC CAVITY • Tegmen Tympani - a thin plate of bone • Formed in part by petrous & part by squamous bone & Petro-squamous suture

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

ANTERIOR WALL OF TYMPANIC CAVITY

LATERAL WALL • Part membranous & Part bony • Tympanic membrane forms the central portion • Above & below – bony outer lateral walls of epitympanum & hypotympanum

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 • Processus cochleariformis – Tendon of tensor tympani takes a turn here

POSTERIOR WALL • • Opening to mastoid antrum Pyramid Facial recess (suprapyramidal recess) Sinus tympani ( infrapyramidal recess)

ENDOSCOPIC VIEW OF POSTERIOR MEDIAL WALL OF TYMPANIC CAVITY

FACIAL RECESS (SUPRAPYRAMIDAL RECESS)

AUDITORY OSSICLES • Conduction of sound waves from the external ear to middle ear • Links the tympanic membrane to oval window and cochlea

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

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

STAPES (STIRRUP) • Consists of a head, neck & crura • Head articulates with incus • Stapedius isertion into posterior part of neck and posterior crura • The 2 crura join the footplate

MUSCLES • Tensor tympani 1 st 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

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 secrotomotor fibres to parotid

LINING OF MIDDLE EAR CLEFT • Eustachian tube-ciliated epithelium • Cartilagenous part by pseudostratified columnar, • Columnar in bony part • Tympanic cavity • Ciliated columnar in anterior and inferior part • Cuboidal in posterior part • Epitympanum and mastoid air cells • Flat non ciliated epihelium

BLOOD SUPPLY OF MIDDLE EAR • Anterior tympanic branch of maxillary artery • Stylomastoid branch of posterior auricular artery

EUSTACHIAN TUBE • Connects the nasopharynx to the Tympanic cavity • 36 mm in length • Runs downwards, forwards and medially • Horizontal, wide and short in infants

• The tympanic end opens into the anterior wall of middle ear • The pharyngeal end opens into the lateral wall of Nasopharynx behind the Posterior end of the inferior turbinate