The ear can be divided into three sections; the external ear, middle ear, and inner ear. This article will focus on the anatomy of the external ear; specifically, its structure, neurovascular supply, and clinical correlations.
The external ear can be further divided into two parts; the auricle (or pinna) and the external acoustic meatus that ends with the tympanic membrane.
The auricle is a paired structure found on each side of the head that captures and directs sound waves to the external acoustic meatus. Most of the auricle is made up of cartilage, with the lobule being the only part not supported by cartilage. The outer curvature of the cartilaginous auricle is called the helix, and the innermost curvature is known as the antihelix. This antihelix divides into two crus; the inferoanterior and the superoposterior crus. In the middle of the auricle is a hollow depression known as the concha. This concha leads to the external acoustic meatus, and directly in front of the beginning of that meatus is an elevation of cartilaginous structure called the tragus. Opposite the tragus is the antitragus.
Auricular hematoma refers to a collection of blood between the cartilage of the ear and the overlying perichondrium. It is often the result of trauma, commonly seen in contact sports such as rugby. The accumulation of blood can disrupt the blood supply to the cartilage, and therefore requires prompt drainage. If untreated it can lead to avascular necrosis of the cartilage, resulting in a disfiguration known as ‘cauliflower ear’.
The external acoustic meatus is a sigmoid shaped tube that extends from the deep part of the concha to the tympanic membrane. The walls of the external 1/3 of this tube are made of cartilage, and the inner 2/3 are made of the temporal bone. This meatus does not run in a straight line, and instead travels in an S-shaped curve, initially in a superoanterior direction, turning slightly to move superoposteriorly, and ending in an inferoanterior direction.
The tympanic membrane lies at the end of the external acoustic meatus and is a connective tissue structure, covered with skin on the outer side and mucous membrane on the inside. The membrane is attached to the surrounding temporal bone by a fibrocartilaginous ring. The translucency of the tympanic membrane allows the structures within the middle ear to be observed during otoscopy. On the inside of the tympanic membrane is where the handle of malleus attaches, at a point called the umbo. This handle of malleus extends superiorly, and its highest point is a small projection called the lateral process of the malleus. Parts of the tympanic membrane that move away from the lateral process are called the anterior and posterior malleolar folds.
The tympanic membrane is a relatively thin connective tissue structure and is therefore susceptible to perforation, usually by trauma or infection. An infection of the middle ear (otitis media) builds up an accumulation of pus and fluid behind the tympanic membrane, which increases pressure and may lead to rupture. In some cases the tympanic membrane may heal itself, but in larger perforations, surgical grafting may be required.
The external ear is made up of several cartilaginous and connective tissue structures. It is responsible for collecting sound waves and conducting them to the middle ear, to be further processed before signals are sent to the brain to be interpreted.
The antihelix divides into two cura; the inferoanterior crus, and the superoposterior crus. In the middle of the auricle is a hollow depression, called the concha. It continues into the skull as the external acoustic meatus. The concha acts to direct sound into the external acoustic meatus. Immediately anterior to the beginning of the external acoustic meatus is an elevation of cartilaginous tissue - the tragus. Opposite the tragus is the antitragus.
The external acoustic meatus is a sigmoid shaped tube that extends from the deep part of the concha to the tympanic membrane. The walls of the external 1/3 are formed by cartilage, whereas the inner 2/3 are formed by the temporal bone.
The external acoustic meatus does not have a straight path, and instead follows a three part S-shaped curve.
The tympanic membrane lies at the distal end of the external acoustic meatus. It is a connective tissue structure, covered with skin on the outside and a mucous membrane on the inside. The membrane is connected to the surrounding temporal bone by a fibrocartilaginous ring. The translucency of the tympanic membrane allows the structures within the middle ear to be observed during otoscopy.
On the inner surface of the membrane, the handle of malleus attaches to the tympanic membrane, at a point called the umbo of tympanic membrane. The handle of malleus continues superiorly, and at its highest point, a small projection called the lateral process of the malleus can be seen. The parts of the tympanic membrane moving away from the lateral process are called the anteiror and posterior malleolar folds.
The tympanic membrane is a relatively thin connective tissue structure, and is susceptible to perforation (usually by trauma or infection). 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.
The external ear is supplied by branches of the external carotid artery:
Venous drainage is via veins following the arteries listed above.
The sensory innervation to the skin of the auricle comes from numerous nerves:
Some individuals can complain of an involuntary cough when cleaning their ears- this is due to stimulation of the auricular branch of the vagus nerve (the vagus nerve is also responsible for the cough reflex).
The lymphatic drainage of the external ear is to the superficial parotid, mastoid, upper deep cervical and superficial cervical nodes.
The anatomy of the outer ear is complex and important to understand in order to diagnose and treat the many conditions it can be subject to. Knowing the structures and vessels that make up the external ear as well as how they are related to each other is the first step to providing appropriate and effective care.
