Anatomy of External Ear

Anatomy of the External Ear

🌬 Divisions of the Ear

The ear can be divided into three main parts:

1. External Ear: Auricle (Pinna) and External Auditory Canal (EAC), ending at the Tympanic Membrane.

2. Middle Ear: From the Tympanic Membrane medially, containing the middle ear cleft and ossicles.

3. Internal Ear: Containing the labyrinth, responsible for hearing and balance.

In this post, we'll focus on the External Ear.

✨ The External Ear: Pinna and EAC

👂 Anatomy of the Auricle (Pinna)

The auricle, or pinna, is the visible projecting part of the external ear. Its primary function is collecting sound waves.

• Surfaces: Has a lateral surface (visible) and a medial (cranial) surface.

📍 Lateral Surface Anatomy:

The lateral surface has distinct prominences and depressions:

• Helix: The curved outer rim.

What is Darwin's Tubercle?

• Antihelix: A curved rim anterior to and parallel to the helix.

  • Divides superiorly into two crura.

  • Triangular Fossa: Enclosed between the two crura of the antihelix.

  • Scaphoid Fossa: Lies superior to the two crura.

• Concha: The large, deep cavity anterior to the antihelix, partly encircled by it.

  • Divided by the Crus of the Helix (anterior superior portion of the helix).

  • Cymba Concha: The smaller, superior portion (lateral relation to the suprameatal triangle).

  • Cavum Concha: The larger, inferior portion.

• Tragus: A small, blunt, triangular cartilaginous prominence anterior to the EAC opening, pointing posteriorly.

• Antitragus: Lies opposite the tragus, at the inferior limit of the antihelix.

• Intertragic Notch: The notch separating the tragus from the antitragus.

• Lobule: The soft, fleshy part below the antitragus (the earlobe).

Clinical Note: The unique pattern of the lateral surface is comparable to fingerprints and can aid in identification.

📍 Medial (Cranial) Surface Anatomy:

The medial surface has elevations corresponding to the lateral depressions (e.g., Eminentia Concha).

Structure of Pinna

1- 🔬 Skin of the Pinna:

• Very thin.

• Lateral Surface: Closely attached to the perichondrium.

• Medial Surface: Slightly loose due to subdermal adipose tissue, which facilitates dissection (e.g., during pinnaplasty).

• Covered with fine hair, mostly in the concha and scaphoid fossa. Thick, coarse hair grows over the tragus and intertragic notch in older males.

• Sebaceous glands open into hair root canals.

2- 🦴 Cartilage of the Pinna:

• Composed of elastic fibrocartilage.

• Forms the entire pinna except for the lobule, which is made of fibrous and adipose tissue.

• Continuous with the cartilage of the external auditory canal.

What is Incisura Terminalis? What is the clinical importance of Incisura Terminalis?

🩸 Perichondrium:

• Covers the cartilage.

• Provides blood supply to the avascular cartilage.

What is Boxer's Ear?

What are the different grafts for Tympanoplasty that can be harvested from the pinna?

🦾 Ligaments of the Pinna:

• Extrinsic Ligaments: Connect the auricular cartilage to the temporal bone.

  • Anterior: From tragus/crus of helix to zygomatic arch root.

  • Posterior: From medial concha to mastoid prominence.

• Intrinsic Ligaments: Connect various parts of the auricular cartilage to each other.

💪 Muscles of the Pinna:

• Extrinsic Muscles: Three muscles radiating from the auricle to the epicranial aponeurosis.

  • Auricularis Anterior: Smallest.
  • Auricularis Superior: Largest, fan-shaped.
  • Auricularis Posterior: Has 2-3 fleshy slips, inserts on the ponticulus.

What is the blood supply and nerve supply of the Extrinsic muscles of pinna?

What are the actions of Extrinsic muscles of pinna?

• Intrinsic Muscles: Six small muscles passing between cartilaginous parts (Helices Major/Minor, Tragicus, Antitragicus, Transversus/Obliquus Auriculae).

  • Responsible for very minimal shape changes.

What is the blood supply and nerve supply of the Intrinsic muscles of pinna?

🩸 Blood Supply of the Pinna:

Mainly from the External Carotid Artery via:

• Posterior Auricular Artery (dominant supply): Supplies most of the medial surface, concha, middle/lower helix, lower antihelix.

• Anterior Auricular Branches of the Superficial Temporal Artery: Supply upper helix/antihelix, triangular fossa, tragus, lobule.

• Superior Auricular Artery: Connects STA and Posterior Auricular networks.

• Small auricular branch from the Occipital Artery (sometimes assists PA in supplying medial surface).

Nerve Supply of the Pinna:

Crucially supplied by branches from multiple cranial and cervical nerves:

• Greater Auricular Nerve
• Lesser Occipital Nerve
• Auricular Branch of Vagus Nerve (Arnold's nerve)
• Auriculotemporal Nerve(Branch of Mandibular division of Trigeminal Nerve)
• Facial Nerve

What are the areas of supply of the above mentioned nerves in the pinna?

🦠 Lymphatic Drainage of the Pinna:

• Posterior/Medial Surface: Drains to Postauricular (Mastoid) lymph nodes.

• Tragus & Upper Anterior Surface: Drains to Preauricular lymph nodes.

• Rest of the Auricle: Drains to Upper Deep Cervical lymph nodes.

🕳️ Anatomy of the External Auditory Canal (EAC)

The EAC is a tube extending from the concha to the tympanic membrane.

• Length: Approximately 2.4 cm.

• Parts:

  • Outer One-Third (Cartilaginous): ~8 mm long.
  • Inner Two-Thirds (Bony): ~16 mm long.

• The anterior wall and floor are about 6 mm longer than the posterior wall and roof.

📏 Direction & Straightening:

• The EAC is S-shaped.

  • Cartilaginous Part: Directed upwards, backwards, and medially.
  • Bony Part: Directed downwards, forwards, and medially.

• To straighten the EAC for examination:

  • Adults: Gently pull the auricle upwards and backwards.
  • Neonates: The bony EAC is undeveloped; the TM is more horizontal. Pull the auricle gently downwards and backwards.

🦴 Parts of the EAC:

• Cartilaginous EAC (Outer 1/3):

  • Continuous with the auricular cartilage.

  • Medial border attached to the bony canal rim by fibrous bands.

  • Contains Fissures of Santorini: Two horizontal fissures anterior-inferiorly.

  • Hair follicles are present ONLY here.

Why do furuncles occur only in the cartilaginous part of EAC?

What infections spread through Fissures of Santorini?

• Bony EAC (Inner 2/3):

  • Lined by very thin skin, continuous with the skin of the tympanic membrane.

  • Devoid of hair and ceruminous/sebaceous glands.

  • Medial end marked by the Tympanic Sulcus (a groove for the TM, absent superiorly).

  • Contains suture lines: Tympanosquamous suture (anteriorly) and Tympanomastoid suture (posteriorly).

  • May have the Foramen of Huschke: A deficiency in the anterior-inferior bony canal wall (common in children up to age 4, sometimes persists in adults).

What infections spreads through the Foramen pf Huschke?

What are the 2 constrictions of the EAC?

🧭 Relations of the EAC:

• Laterally: Opens to the outside world (at the concha).
• Medially: The Tympanic Membrane and Middle Ear.
• Posteriorly: Mastoid bone.
• Anteriorly: Temporomandibular Joint (TMJ), Superficial Temporal Artery & Vein, Auriculotemporal nerve, Parotid gland, Preauricular lymph nodes.
• Superiorly: Middle Cranial Fossa.
• Inferiorly: Jugular bulb, Carotid artery, Facial nerve, Styloid process, Parotid gland, Digastric muscle.

🔬 Lining Epithelium of EAC:

• Lined with keratinizing stratified squamous epithelium.

• Unique property: Outward and oblique growth/migration of the epidermis (approx. 0.1 mm/day).

• Short hair projects laterally at the opening.

🧬 Appendages:

Located in the cartilaginous EAC only:

• Ceruminous glands: Modified sweat glands, secrete cerumen.

• Pilo-sebaceous glands: Secrete sebum.

• Wax (Cerumen): Mixture of desquamated cells, cerumen, and sebum.

  • Varieties: Dry (yellowish/grey) and Wet (yellowish-brown, sticky).

🩸 Blood Supply of the EAC:

Derived from the External Carotid Artery:

• Auricular branches of the Superficial Temporal Artery: Supply the roof and anterior part.

• Deep Auricular Branch of the Maxillary Artery: Supplies the anterior meatal wall skin and the outer surface epithelium of the TM.

• Auricular branches of the Posterior Auricular Artery: Supply the posterior part.

• Veins: Drain into the External Jugular Vein, Maxillary veins, and Pterygoid plexus.

Nerve Supply of the EAC:

• Auriculotemporal Nerve (Branch of Mandibular division of Trigeminal Nerve): Supplies the anterior wall and roof.

• Auricular Branch of Vagus Nerve (Arnold's Nerve): Supplies the posterior wall and floor.

• Facial Nerve: Supplies a small portion of the posterior wall (via communicating branches, often reaching via the auricular branch of the Vagus).

What is Hitzelberger Sign?

Which nerve stimulation in EAC causes Vasovagal Reflex?

What findings in EAC do you find in Ramsay-Hunt Syndrome and why?