Last revised by Arlene Campos on 12 Jan 2024

The inion (plural: inia/inions) is the tip of the external occipital protuberance (EOP), the midline bony prominence in the occipital bone from which the ligamentum nuchae and trapezius muscle attach. It is usually easily palpable.

Clinical importance

The inion the surface marking of the internal attachment of the tentorium cerebelli. It is one of the skull landmarks, craniometric points for radiological or anthropological skull measurement.

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Cases and figures

  • Figure 1: skull landmark images
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  • Case 1: massive EOP
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