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Auricle (Pinna)

The auricle—also known as the pinna—is the visible, cartilaginous external part of the ear. It plays a critical role in collecting and directing sound waves into the external auditory canal. The auricle’s complex shape aids in sound localization and its structure is mainly composed of elastic cartilage, covered by skin, with various named landmarks such as the helix, antihelix, tragus, and lobule.

Synonyms:

  • Pinna

  • External ear (in reference to its visible part)

  • Auricula

MRI Appearance of the Auricle:

Proton Density (PD) Sequence:

  • Auricle appears as a thin, well-defined structure surrounding the external auditory canal.

  • Cartilage of the auricle shows intermediate signal intensity on PD images, differentiating it from the adjacent soft tissue and air.

  • Overlying skin appears as a thin, low signal intensity line.

  • Fat lobule at the lower margin (earlobe) displays high signal due to fat content.

  • No abnormal thickening, mass, or increased signal should be present in normal cases.

Short Tau Inversion Recovery (STIR) Sequence:

  • Auricular cartilage demonstrates intermediate to low signal intensity (slightly darker than surrounding soft tissue).

  • Overlying skin remains low signal.

  • Fat lobule remains high signal (suppressed in STIR, so will appear dark).

  • No high signal abnormality in the cartilage or surrounding soft tissue should be seen in a healthy auricle.

  • STIR is sensitive for edema or inflammation; in pathology (e.g., perichondritis), increased high signal would be observed in the affected areas.

MRI images

Auricle (Pinna)