anatomy of the external and middle ear
TRANSCRIPT
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