Foramen magnum

The foramen magnum is the largest foramen of the skull and is part of the occipital bone . It is oval in shape with a large anteroposterior diameter .

Gross anatomy

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

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

Radiographic features

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

Related pathology