What is the anatomy of the external ear?

External Ear Anatomy

Structural Components

The external ear consists of two main anatomical divisions: the auricle (pinna) and the external auditory canal (EAC), extending from the visible outer ear to the tympanic membrane. 1, 2

The Auricle (Pinna)

• The auricle is composed of elastic cartilage covered by skin, with the notable exception of the earlobe, which lacks cartilage and contains only a small amount of subcutaneous fat 1
• The skin covering the auricle is thin and tightly adherent to the underlying perichondrium 1
• Due to its exposed position, the auricle is particularly vulnerable to ultraviolet light exposure, environmental trauma, and temperature extremes 1
• The auricle develops from six mesenchymal hillocks during embryonic weeks 3-12, which explains why congenital malformations occur in approximately 1 out of 12,500 births 3

The External Auditory Canal

The EAC is divided into two distinct segments: an outer cartilaginous portion (lateral one-third) and an inner bony (osseous) portion (medial two-thirds). 1, 2, 4

Cartilaginous Canal (Lateral Third)

• The cartilaginous canal contains hair follicles, sebaceous glands (producing lipids), and specialized apocrine glands called ceruminous glands that produce cerumen (earwax) 1, 4
• The skin in this region is thicker and more mobile, with a well-developed subcutaneous layer 4
• This portion is more susceptible to inflammatory conditions like acute otitis externa due to the presence of glands and hair follicles 5, 1

Bony (Osseous) Canal (Medial Two-Thirds)

• The osseous canal is formed by the tympanic ring, an incomplete cylinder of membranous bone that develops separately from the auricle 3
• Critically, the bony canal contains neither hair follicles nor glands—the skin here is thin and tightly adherent to the underlying periosteum 1, 4
• This anatomical difference explains why infections in the medial canal can be more severe and why debris removal (aural toilet) is essential before treatment 5, 6

Anatomical Orientation and Course

• The EAC follows an S-shaped anteroposterior course that is poorly visualized on traditional frontal or sagittal views—axial (transverse) imaging provides superior visualization 7
• The canal is approximately 2.5 cm in length in adults, with the lateral cartilaginous portion measuring about 8 mm and the medial bony portion about 16 mm 4
• The canal is not straight but curves, requiring gentle traction of the auricle upward and backward in adults (or downward and backward in children) for proper otoscopic examination 4, 7

Vascular Supply and Innervation

• The auricle receives blood supply from branches of the external carotid artery (posterior auricular and superficial temporal arteries) 7
• Sensory innervation is complex, involving the great auricular nerve (C2-C3), auriculotemporal nerve (V3), and branches of cranial nerves VII and X, which explains why ear pain can be referred from distant sites like the temporomandibular joint, pharynx, or teeth 5, 7

Clinical Relevance

• The presence of hair follicles and glands in the cartilaginous canal makes this region susceptible to bacterial invasion when the epithelial barrier is disrupted by water exposure, trauma, or dermatologic conditions 5
• The hallmark sign of external ear canal inflammation (acute otitis externa) is intense tenderness when the tragus is pushed or the pinna is pulled, often disproportionate to visual findings 5
• The tight adherence of skin to bone in the osseous canal means that edema in this region can be extremely painful and may require wick placement to facilitate medication delivery 6