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Topic

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External occipital protuberance

The external occipital protuberance (EOP) is a bony prominence on the midline of the occipital bone at the posterior skull, located at the junction of the superior nuchal line and the midline squamous portion of the occipital bone. It is typically palpable as a small, rounded bump, with size and shape varying between individuals. The EOP serves as an attachment point for the ligamentum nuchae and several posterior neck muscles, including the trapezius. It also contributes to the overall contour and curvature of the posterior skull, acting as an important skeletal landmark in anthropometry, neurosurgery, and radiology.

Synonyms

  • Occipital tubercle

  • Inion (tip of the EOP)

  • External occipital tuberosity

Function

  • Serves as an attachment site for the ligamentum nuchae, stabilizing the head and neck

  • Provides origin for posterior neck muscles, including the trapezius

  • Contributes to posterior skull contour and cranial shape

  • Acts as a reliable landmark for cranial measurements and neurosurgical orientation

MRI Appearance
T1-weighted images:

  • Appears as a hypointense bony structure at the midline of the occipital bone

  • Surrounded by subcutaneous soft tissue and occipital muscles, which are intermediate to hyperintense

  • Fractures or bony lesions appear as disruption of the cortical low signal

T2-weighted images:

  • Bone is hypointense, while surrounding soft tissue and muscle appear intermediate to slightly hyperintense

  • Useful for identifying bone marrow edema or post-traumatic changes

STIR (Short Tau Inversion Recovery):

  • Fat suppression enhances detection of bone marrow edema, soft tissue swelling, or inflammation

  • Normal EOP appears hypointense; abnormal hyperintensity indicates trauma, infection, or neoplasm

CT Appearance

  • Appears as a hyperdense, well-corticated midline bony prominence on the posterior skull

  • Easily visualized in axial, sagittal, and 3D reconstructed images

  • Surrounding soft tissue and subcutaneous fat provide natural contrast

MRI images

External occipital protuberance mri axial image -img-00000-00000