The External Ear

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The ear is divided into three sections: outside, center, and within. The anatomy of the external ear, including its structure, neurovascular supply, and clinical consequences, will be covered in this article.

The two functional and anatomical parts of the external ear are the auricle (or pinna) and the external auditory meatus, which terminates at the tympanic membrane.

Auricle

The auricle is a paired structure that can be seen on both sides of the skull. Sound waves are captured and sent to the external acoustic meatus.

It is primarily cartilaginous, with the lobule being the only component that is not supported by cartilage. The helix is an exterior curvature formed by the cartilaginous component of the auricle. The antihelix is a second deepest curvature that runs parallel to the helix. The antihelix is divided into two cura: inferoanterior and superoposterior crus.

The concha is a hollow indentation in the centre of the auricle. It continues as the external acoustic meatus into the skull. The concha is responsible for directing sound into the external acoustic meatus. The tragus is an elevation of cartilaginous tissue located immediately anterior to the beginning of the external acoustic meatus. The antitragus is the inverse of the tragus.

Auricle-or-Pinna-of-the-Ear-Labelled-Diagram.
Fig 2 – Anterior surface of the auricle of the external ear.

Clinical Relevance: Auricular Haematoma

The accumulation of blood can disrupt the blood supply to the cartilage, and requires prompt drainage. Untreated cases can result in avascular necrosis of the cartilage, resulting in a ‘cauliflower ear’ deformity.

External Acoustic Meatus

The external acoustic meatus is a sigmoid-shaped tube that runs from the concha’s deep section to the tympanic membrane. The external third’s walls are made of cartilage, while the inside two-thirds are made of temporal bone.

The exterior acoustic meatus does not travel in a straight line but rather in an S-shaped curve, as seen below:

It moves in a superoanterior direction at first.

It then makes a modest turn to travel superoposteriorly.

It eventually runs in an inferoanterior orientation.

Tympanic Membrane

At the distal end of the external acoustic meatus is the tympanic membrane. It is a connective tissue structure that is covered on the outside by skin and on the inside by a mucous membrane. A fibrocartilaginous ring connects the membrane to the surrounding temporal bone.

The tympanic membrane’s translucency permits components within the middle ear to be seen during otoscopy. The handle of malleus joins to the tympanic membrane on the inner surface of the membrane at a position known as the umbo of tympanic membrane.

The malleus handle continues superiorly, and at its highest point, a tiny protrusion known as the malleus lateral process can be detected. The anterior and posterior malleolar folds are the sections of the tympanic membrane that move away from the lateral process.

The exterior acoustic meatus does not travel in a straight line but rather in an S-shaped curve, as seen below:

It moves in a superoanterior direction at first.

It then makes a modest turn to travel superoposteriorly.

It eventually runs in an inferoanterior orientation.

Anterior-Surface-of-the-Tympanic-Membrane-
Fig 3 – The tympanic membrane of the ear.

Clinical Relevance: Perforation of the Tympanic Membrane

An infection of the middle ear (otitis media) causes pus and fluid to build up behind the tympanic membrane. This causes an increase in pressure within the middle ear, and eventually the eardrum can rupture.

In some cases the tympanic membrane heals itself, but in larger perforations surgical grafting may be required.

Vasculature

The external ear is supplied by branches of the external carotid artery:

  • Posterior auricular artery
  • Superficial temporal artery
  • Occipital artery
  • Maxillary artery (deep auricular branch) – supplies the deep aspect of the external acoustic meatus and tympanic membrane only.

Venous drainage is via veins following the arteries listed above.

Innervation

The sensory innervation to the skin of the auricle comes from numerous nerves:

  • Greater auricular nerve (branch of the cervical plexus) – innervates the skin of the auricle
  • Lesser occipital nerve (branch of the cervical plexus) – innervates the skin of the auricle
  • Auriculotemporal nerve (branch of the mandibular nerve) – innervates the skin of the auricle and external auditory meatus.
  • Branches of the facial and vagus nerves – innervates the deeper aspect of the auricle and external auditory meatus

When cleaning their ears, some people experience an involuntary cough, which is caused by stimulation of the vagus nerve’s auricular branch (the vagus nerve is also responsible for the cough reflex).

Lymphatics

External ear lymphatic drainage goes to the superficial parotid, mastoid, upper deep cervical, and superficial cervical nodes.