Applied anatomy of external ear with emphasis on divisions of external ear - pinna, external auditory canal, tympanic membrane with their structure and clinical aspects with mention about otoscopy

1. Applied anatomy of external ear
Adhavan. M
2nd year MBBS
IGMC&RI
Puducherry

2. External ear
Pinna External auditory meatus Tympanic membrane
•Helix
•Anti-helix
•Tragus
•Anti-tragus
•Concha
•Cymba conchae
•Incisura terminalis
Cartilagenous part Bony part Pars flaccida Pars tensa

3. Pinna
•Single folded piece
of cartilage
•Skin adherent to
perichondrium
•Epithelium: Stratified
squamous
keratinised
•Lobule - adipose
tissue, no cartilage
Incisura terminalis
Cymba conchae

4. Applied aspects
• Endaural incission - Made in incisura terminalis for surgery of EAC and
middle ear; doesn’t cut through auricular cartilage
• Frostbite - outer surface more prone - as skin is adherent to
perichondrium - no subcutaneous tissue
• Grafts in rhinoplasty - conchal cartilage to correct depressed nasal
bridge; skin and cartilage for defects in ala of nose
• Grafts in tympanopathy - tragal and conchal cartilage, perichondrium
and fat from lobule are used

5. External auditory canal
• 24mm long
• Extends from concha to TM
• 2 parts - Cartilagenous and bony
• S shaped, not straight
• Examination - pinna is pulled upward, backward and laterally to
make the canal straight

6. • Lateral 1/3
• Continuation of pinna
• Directed upward, backward and medially
• Contains hair follicles, sebaceous and ceruminous glands
• Fissures of Santorini - transverse slits in the anterior inferior
wall of cartilagenous EAC - passage of infections and
neoplasm to and from EAC to surrounding tissues (parotid and
base of skull)
• Furuncles/folliculitis - bacterial infection of hair follicles are
common
Cartilagenous EAC

7. • Medial 2/3
• Enclosed within temporal bone
• Directed downward, forward and medially
• Isthmus - 6mm lateral to TM - narrowest part - foreign bodies
impacted medial are difficult to remove
• Foramen of huschke - deficiency in anteroinferior bony EAC -
spread of infection to and from parotid and TM joint
• In acute mastoiditis - sagging of posterior-superior part of
deeper bony EAC due to relation with mastoid antrum
Bony EAC

8. • Epithelial migration - self cleansing mechanism - sloughed
epithelium extruded out with cerumen
• Hitzelberger’s sign - hypoesthesia of posterior meatal wall due to
pressure of facial nerve in patients with acoustic neuroma
• Vasovagal reflex - cough, bradycardia, syncope, cardiac arrest
during cleansing of EAC due to Vagus nerve
• Ramsay hunt syndrome - Vesicles of herpes zoster occur on
mastoid and posterior meatal wall indicating facial nerve
innervation
Bony EAC contd.

9. Tympanic membrane
• Window between external and middle ear
• Height - 9 to 10 mm
• Width - 8 to 9 mm
• Thickness - 0.1 mm
• Position - oblique - 55° with deep EAC, postero-superior part
is more lateral
• Parts - Pars tensa and pars flaccida

10. Pars tensa
• Lower 2/3
• Annulus tympanicus - peripheral thickened part of TM forms
fibrocartilagenous ring, fits in tympanic sulcus
• Umbo - central part of TM - near tip of malleus - is tented inwards
• Cone of light - bright part of light radiating from tip of malleus to
periphery in anterioinferior quadrant seen in otoscopy

12. Pars flaccida
• A.k.a. Shrapnell’s membrane
• Upper 1/3 of TM
• Less tense than pars tensa
• Appears pinkish in otoscopy

13. Structure of TM
• 3 layers
• Outer epithelial layer - continuous with EAC skin
• Middle fibrous layer - encloses handle of malleus
• Inner mucosal layer - continuous with middle ear mucosa

14. Ottoscopy
• Normal TM is shiny and pearly
grey
• Concave laterally
• Transparency of TM varies from
person to person
• Some middle ear structures are
usually seen through TM