Foramen magnum

The foramen magnum is the largest foramen of the skull and is part of the occipital bone 1. It is oval in shape with a large antero-posterior diameter 2.

Gross Anatomy

The foramen magnum is found in the most inferior part of the posterior cranial fossa 3.  It is traversed by vital structures including the medulla oblongata 1. In the midline, the anterior margin is the basion and the posterior marging is the opisthion.

  • anteriorly - basilar part of occipital bone
  • anterolaterally - occipital condyles, hypoglossal canal, jugular foramen
  • posteriorly - squamous part of occipital bone with the internal occipital crest

Radiographic features

  • at the level of the foramen magnum CSF is seen to surround the medulla which is reduced or absent in tonsillar herniation

Related Pathology

Related articles

Head and neck anatomy

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