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External ear summarise in exam point of view to write in 4 mins important points
Here's a high-yield exam summary of the External Ear based on your textbook images:
EXTERNAL EAR - Exam Summary (4-min write)
Components
- Pinna (Auricle)
- External Auditory Meatus (EAM)
- Tympanic Membrane
PINNA / AURICLE
Structure: Fibroelastic cartilage (except lobule = fibrofatty tissue) covered with skin
Key Surface Landmarks (lateral surface):
- Concha - large depression leading into EAM; guarded by tragus
- Helix - peripheral rim; anterior limb = crus of helix; posterior limb ends as ear lobe
- Darwin's tubercle - small elevation on upper posterior helix (vestige of pointed quadruped ear)
- Antihelix - ridge parallel to helix; upper end splits into 2 crura enclosing triangular fossa
- Scaphoid fossa - gutter between helix and antihelix
- Tragus - small triangular flap in front of concha
- Antitragus - opposite tragus; separated by intertragic notch
- Cymba conchae - small area above crus of helix = corresponds to suprameatal triangle (McEwen's triangle)
- Lobule - fibrofatty, no cartilage
N.B.: No cartilage between tragus and crus - gap = incisura terminalis (surgical incision site for EAM surgery)
Medial surface: Eminentia concha + Eminentia triangularis
MUSCLES
- Extrinsic: Auricularis anterior, superior, posterior (all supplied by facial nerve)
- Intrinsic: Small slips between cartilaginous parts
NERVE SUPPLY OF PINNA
| Surface | Area | Nerve |
|---|---|---|
| Lateral | Lower 1/3 | Great auricular (C2, C3) |
| Lateral | Upper 2/3 | Auriculotemporal (V3) |
| Lateral | Concha | Auricular branch of vagus (CNX) |
| Medial | Lower 1/3 | Great auricular (C2, C3) |
| Medial | Upper 2/3 | Lesser occipital (C2) |
| Medial | Eminentia conchae | Auricular branch of vagus (CNX) |
Motor: Facial nerve (CN VII) to all auricular muscles
ARTERIAL SUPPLY
- Posterior auricular artery (branch of external carotid) - cranial surface + posterior lateral surface
- Superficial temporal artery - anterior lateral surface
- Few branches of occipital artery - upper cranial surface
Lymphatics: Preauricular (parotid), mastoid, upper deep cervical nodes
EXTERNAL AUDITORY MEATUS (EAM)
- Length: ~24 mm (posterior wall)
- S-shaped course: outer part - upward, backward, medially (UBM); inner part - downward, forward, medially (DFM)
- To examine TM: Pull pinna upward, backward, laterally (adults) / downward & backward (infants)
Two Parts:
| Cartilaginous | Bony | |
|---|---|---|
| Length | Outer 1/3 (8 mm) | Inner 2/3 (16 mm) |
| Skin | Thick, with hair + ceruminous glands | Thin, no hair/glands |
| Narrowing | - | Isthmus (4 mm from TM) - FB gets impacted here |
Foramen of Huschke - on anterior wall of bony part; present in children up to 4 years (allows parotid infection to spread)
Nerve Supply of EAM:
- Roof + anterior wall: Auriculotemporal nerve (V3)
- Floor + posterior wall: Auricular branch of vagus (CNX) - ONLY cutaneous branch of vagus
- Clinical: syringing EAM → cough, vomiting (Arnold's reflex)
TYMPANIC MEMBRANE
- Size: 9-10 mm long, 8-9 mm wide, 0.1 mm thick
- Angle: 55° with floor of EAM
- Position: Oblique - faces downward, forward, laterally
3 Layers (lat to med):
- Outer cuticular layer (stratified squamous epithelium) - from ectoderm
- Middle fibrous layer (radial + circular fibres, encloses handle of malleus) - from mesoderm
- Inner mucosal layer (low columnar epithelium) - from endoderm
Two Parts:
- Pars tensa (most of TM) - periphery thickened as annulus tympanicus in tympanic sulcus
- Pars flaccida (Shrapnell's membrane) - small triangular area above anterior & posterior malleolar folds; NO intermediate fibrous layer; appears pinkish
Surfaces:
- Lateral surface: concave
- Medial surface: convex; point of maximum convexity = Umbo (where handle of malleus attaches)
- Cone of light - reflected in anteroinferior quadrant at 5 o'clock position
4 Quadrants (divided by 2 imaginary lines through umbo):
- Posterosuperior (1)
- Anterosuperior (2)
- Posteroinferior (3)
- Anteroinferior (4) - cone of light here; myringotomy done here to avoid chorda tympani
On otoscopy, visible structures:
- Handle of malleus (yellow streak from umbo upward)
- Lateral process of malleus (white prominence above)
- Long process of incus (behind/parallel to upper malleus handle)
- Cone of light (anteroinferior)
- Pars flaccida
Nerve Supply of TM:
- Anterior half (lateral): Auriculotemporal (V3)
- Posterior half (lateral): Auricular branch of vagus (CNX)
- Medial surface: Tympanic branch of glossopharyngeal (CN IX) via tympanic plexus
HIGH-YIELD CLINICAL POINTS
- Ramsay Hunt Syndrome - Herpes zoster of geniculate ganglion; vesicles in concha + eminentia conchae (auricular branch of facial nerve territory)
- Furunculosis - only in outer cartilaginous part (where hair follicles present)
- EAM infection/boil - very painful (skin firmly adherent to cartilage/bone)
- Isthmus - foreign body impaction site
- Myringotomy - posteroinferior quadrant (avoids chorda tympani)
- Atresia of EAM - failure of canalization of meatal plug
- Accessory auricles - failure of fusion of 6 mesodermal tubercles
- EAM development - ectodermal invagination of 1st pharyngeal cleft
- Pinna development - 6 mesodermal tubercles around 1st pharyngeal cleft
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