Foramen magnum

Dr Craig Hacking and Dr Julian Maingard et al.

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.

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 margin 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
  • at the level of the foramen magnum CSF is seen to surround the medulla which is reduced or absent in tonsillar herniation
Anatomy: Head and neck
Share article

Article information

rID: 25317
Section: Anatomy
Synonyms or Alternate Spellings:

Support Radiopaedia and see fewer ads

Cases and figures

  • Skull base inferi...
    Figure 1: inferior view
    Drag here to reorder.
  • Skull base superi...
    Figure 2: superior view
    Drag here to reorder.
  • Updating… Please wait.

     Unable to process the form. Check for errors and try again.

     Thank you for updating your details.