M01.02.027 The External Ear

The ear is divided into three parts: external, middle, and inner. This article focuses on the anatomy of the external ear, highlighting its structure, neurovascular supply, and clinical correlations.

Structure of the External Ear

The external ear is functionally and structurally divided into two components:

1. Auricle (Pinna)
2. External Acoustic Meatus

These structures terminate at the tympanic membrane.

Auricle (Pinna)

• Function: Captures and directs sound waves toward the external acoustic meatus.
• Structure:
  • Predominantly cartilaginous except the lobule (non-cartilaginous).
  • Helix: Outer curvature.
  • Antihelix: Inner curvature, dividing into two crura:
    • Inferoanterior crus
    • Superoposterior crus
  • Concha: Central hollow depression leading to the external acoustic meatus.
  • Tragus: Cartilaginous elevation anterior to the meatus.
  • Antitragus: Opposite the tragus.

Clinical Relevance: Auricular Haematoma

• Definition: Blood accumulation between ear cartilage and perichondrium due to trauma (e.g., contact sports like rugby).
• Complications: Disruption of blood supply, leading to avascular necrosis and a “cauliflower ear” deformity.
• Management: Prompt drainage is essential.

External Acoustic Meatus

• Function: Conducts sound waves to the tympanic membrane.
• Structure:
  • Outer 1/3: Cartilaginous walls.
  • Inner 2/3: Bony walls (temporal bone).
  • Shape: S-shaped curve with three directional changes:
    1. Superoanteriorly
    2. Superoposteriorly
    3. Inferoanteriorly

Tympanic Membrane

• Function: Separates the external ear from the middle ear and transmits sound vibrations.
• Structure:
  • Layers:
    • External: Skin.
    • Internal: Mucous membrane.
  • Attachment: Connected to the temporal bone by a fibrocartilaginous ring.
  • Landmarks:
    • Umbo: Attachment point of the malleus.
    • Lateral Process of Malleus: Visible small projection.
    • Malleolar Folds: Anterior and posterior folds radiating from the lateral process.

Clinical Relevance: Perforation of the Tympanic Membrane

• Causes: Trauma or infection (e.g., otitis media).
• Symptoms: Pain, hearing loss, possible infection spread.
• Management: Small perforations may heal; larger ones may need surgical grafting.

Neurovascular Supply of the External Ear

Arterial Supply

The external ear receives blood from branches of the external carotid artery:

Venous Drainage

Venous drainage corresponds to the arterial supply via similarly named veins.

Innervation

Note: Stimulation of the auricular branch of the vagus nerve may trigger an involuntary cough (Arnold’s reflex).

Lymphatic Drainage

Points to Remember

• The auricle’s primary function is sound wave collection, while the external acoustic meatus conducts sound.
• The tympanic membrane is crucial for sound transmission and is prone to perforation.
• Auricular hematoma requires urgent treatment to prevent cartilage necrosis.
• Innervation of the external ear is complex, involving multiple cranial and spinal nerves.
• Lymphatic drainage is key in monitoring infections or malignancies.

References

1. TeachMeSeries Ltd. (2024). Anatomy of the External Ear.
2. Kayyam, E. [CC BY-SA 3.0]. Via Wikimedia Commons.
3. Emad Kayyam’s anatomical illustrations.