ANATOMY OF THE EXTERNAL ANATOMY OF THE EXTERNAL AND MIDDLE EARAND MIDDLE EAR

DR. SHWETA SHARMAModerator : DR. KANWAR SEN

DEVELOPMENT

EXTERNAL EAR - Auricle

6 Hillocks of His

EAC & MIDDLE EAR 1st pharyngeal pouch endoderm forms:Lining of middle ear

(tympanic cavity)Connection to pharynx

elongates and forms eustachian tube

• Tympanic Membrane– Inner layer endoderm– Middle layer mesoderm– Outer layer ectoderm

1st and 2nd pharyngeal arch cartilage (mesoderm) --> ossicles

• 1st (Meckel’s): epitypanum Part of ossicles– Head of malleus, body and short process of incus

• 2nd (Reichert’s): mesotympanum part of ossicles– Long process malleus, long process incus, stapes

superstructure

• Stapes footplate: otic capsule

Ossicles full sized by 15 weeks

Ossify by 25 weeks

BLOOD SUPPLYBLOOD SUPPLY

NERVE SUPPLYNERVE SUPPLY

Lymphatic DrainageLymphatic Drainage

EXTERNALAUDITORY

CANAL•“S” shaped , 2.4cm

LATERAL 1/3CARTILAGE

•Inwards, slightly downwards & forwards ₦

•8mm

MEDIAL 2/3BONE

•1.6mm•Narrower

•Tympanic sulcus•Roof•Suture line•Constrictions•maturation

GLANDS

• Ceruminous glands = modified apocrine glands

• Sebaceous gland = oily material (sebum) of their fat containing cells

• EAR WAX ??? • INHERITANCE ??? • Is it normal if found on upper portion of

tympanic membrane?

Blood supply: •Outer part by superficial temporal and posterior

auricular arteries.•Inner part by deep auricular branch of maxillary

artery. Lymphatic drainage:

• Preauricular, postauricular and superficial cervical lymph nodes.

Nerve supply: • Anterior by auriculotemporal nerve & greater

auricular (c2, c3) and posterior half by auricular branch of vagus & twig from facial nerve.

2’, 5’, 8’, 11’o clock

MIDDLE EAR CLEFTMIDDLE EAR CLEFT

• TYMPANIC CAVITYTYMPANIC CAVITY• EUSTACHIAN TUBEEUSTACHIAN TUBE• MASTOID AIR CELLSMASTOID AIR CELLS

TYMPANIC TYMPANIC CAVITYCAVITY

•Roughly cuboidal•Roof is wider than floor•Anterior wall narrower than posterior•Medial and lateral wall bear their convexities

LATERAL WALL• Scutum ₦• Anterior

canaliculus• Chorda

tympani

TYMPANIC MEMBRANE

9-10 mm

8-9 mm

• Notch of rivinus, Malleolar folds, Pars flaccida, Pars tensa

• Layers

• Lamina propria of pars tensa

• Maturation/cell division

About 55 degrees

Three recess

• Anterior

• Posterior

• Prussak’s pouch (above lateral processs of malleus and b/w neck of malleus and pars flaccida)

ROOFROOF

• TEGMEN TYMPANI

Petrous & squamous temporal bone ₦

FLOORFLOOR• Variations

• Tympanic branch of gloossopharyngeal nerve pierces between the jugular fossa and lower opening of the carotid canal

Anterior wall

• Upper part

• Lower part

Coronal section at level of long

process of incus

POSTERIOR WALL (MASTOID)POSTERIOR WALL (MASTOID)

• Aditus

• Fossa incudis

• Vertical bony canal

MEDIAL WALL (LABYRINTHINE)MEDIAL WALL (LABYRINTHINE)

Fallopian canal and processus cochleariformis

promontory

FACIAL RECESS

At level of pyramid

where facial recess is

deep

• 3.25 mm long and 1.75 wide.

• Kidney shaped

Fenestra vestibuli/ovalis

Fenestra cochleae / rotunda

• 2.3 X 1.9 mm• A plane at

right angle to stapes footplate

• Closed by secondary tympanic membrane

RELATIONS

•Ossicles•Muscles•Nerve•Mucosa

OssiclesOssicles

• Malleus

• Incus

• stapes

Malleus

•Largest of three•9 mm •Amputation of head by cutting through the neck leaves CT & TT intact

Incus

• Short limb connected to posterior wall

Stapes

•Smallest bone in body•S. tn attaches to posterior part of neck & post. Crus.•Footplate 3mm long X 1.4mm wide•Axis almost horizontal

Joints

Chorda tympani, stapedius, tensor tympani, tympanic plexus

MUCOSAL FOLDS

• Constitution ??

• Origin ??

• pathways

Mucosal folds most commonly seen

1. Tensor tympani fold

2. Lateral incudal fold

3. Medial incudal fold

4. Lateral malleolar fold

5. Stapedial fold

6. Obturator fold

EUSTACHIAN TUBE

• about 36 mm• its direction is downward,

forward, and medialward• forming an angle of about

45 degrees with the sagittal plane and one of from 30 to 40 degrees with the horizontal plane

• It is formed partly of bone (12mm), partly of cartilage and fibrous tissue (24mm)

Base lies directly under the mucous membrane of the nasal part of the pharynx, where it forms an

elevation, the torus tubarius or cushion,behind the pharyngeal orifice of the tube.

The mastoid air cell systemThe mastoid air cell system

• Petrous part of temporal bone• Development• Volume• Well

pneumatised>>diploetic>>sclerotic• epithelium

RELATIONS

Thank you