External auditory canal

Last revised by Bahman Rasuli on 5 Apr 2021

The external auditory canal (EAC) or external auditory meatus (EAM) extends from the lateral porus acusticus externus medially to the tympanic membrane.

As the term external auditory meatus is variably used to refer to the canal itself or the porus acusticus externus (the round lateral opening), it may be better to use the term external auditory canal rather than meatus to avoid potential confusion. 

The external auditory canal is typically 2.5 cm in length and is S-shaped. 

The lateral one-third is bounded by a fibrocartilaginous tube continuous with the auricle 3. Defects in the cartilaginous part of the canal, which allow transmission of infection and malignancy, are known as fissures of Santorini.

The medial two-thirds is surrounded by bone. The anterior wall, floor, and lower part of the posterior wall arise from the tympanic part of the temporal bone 3,4. The roof and upper part of the posterior wall arise from the squamous part of the temporal bone 4. The skin of this inner part is directly applied to periosteum, with no subcutaneous tissue present. A normal variant defect in the anteroinferior aspect of the osseous part of the canal that connects with the temporomandibular joint is known as the foramen tympanicum (foramen of Huschke).

The narrowest part of the external auditory canal is called the isthmus and lies at the junction of the cartilaginous and bony portions of the canal 5.

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Cases and figures

  • Figure 1: external ear anatomy (CT)
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  • Case 1: external acoustic meatus (normal)
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