Jugular Foramen

Overview

A large foramen in the medial-inferior surface of the petrous pyramid of the temporal bone at the base of the skull. It is a transition zone between structures of the ear, posterior fossa and cervical region.

Structure 

The jugular foramen is divided into two parts by a fibrous dural or bony septum, called the jugular spine, into:

• Pars nervosa – The anteromedial portion of the jugular foramen and is smaller than the posterolateral pars vascularis
• Pars vascularis – The posterolateral portion of the jugular foramen and is the larger component.

On its intracranial surface, the roof of the jugular foramen is divided into the pyramidal fossa, intrajugular process, and jugular notch, covering the pars nervosa, dural septum, and pars vascularis. The deep end of the pyramidal fossa lodges the opening of the canaliculus cochleae.

On its extracranial surface, the jugular foramen has an oblique course from medial to lateral and from posterior to anterior.

Contents

Pars nervosa

• Inferior petrosal sinus – drains the cavernous sinus and courses in the petro-occipital fissure adjacent to the clivus prior to its exit through the pars nervosa and subsequent drainage into the internal jugular vein beneath the foramen.
• Glossopharyngeal nerve (CN IX)
  • Enters anterior, medial and superior to the vagus and accessory nerve at the level of the pyramidal fossa 
  • Gives off a tympanic branch (Jacobson nerve) at the level of the inferior ganglion, entering the inferior tympanic canaliculus to form the tympanic plexus to form the lesser petrosal nerve in the middle fossa
  • It reaches and supplies the middle ear along with the inferior tympanic artery via the inferior tympanic canaliculus which is occasionally seen at CT in cross-section at the level of the caroticojugular spine.
  • The tympanic branch of the glossopharyngeal nerve (Jacobson’s nerve) branches off at the level of the inferior ganglion, entering the inferior tympanic canaliculus to form the tympanic plexus to form the lesser petrosal nerve in the middle fossa. 
• Meningeal branches of the ascending pharyngeal artery

Pars vascularis

• Jugular bulb
  • A venous expansion (measuring approximately 15 mm wide x 20 mm high) lodged within and occupying most of the jugular fossa
  • Formed by the union of the sigmoid sinus and the inferior petrosal sinus. It continues as the internal jugular vein
  • Lies lateral to all the nerves within the jugular foramen
• Vagus nerve (CN X)
  • Enters at the level of the intrajugular process 
  • The vagus nerve gives off an auricular branch (Arnold nerve) via the mastoid canaliculus on the lateral wall of the foramen adjacent to the mastoid segment of the facial nerve.
  • The auricular branch of the vagus nerve (Arnold’s nerve) is also formed at the level of the jugular foramen, from the superior ganglion of the vagus and inferior ganglion of the glossopharyngeal nerves, passing through the mastoid canaliculus in direction to the external auditory canal, crossing the mastoid segment of the facial nerve (and giving off a small branch).
• Accessory nerve (CN XI)

Relations

Anteromedially

• Internal carotid artery – enters the skull through the carotid canal of the petrous bone, three segments are identified: ascending (vertical), genu and horizontal portion, passing anterior to the tympanic cavity, eustachian tube and labyrinth.
• It is located posterior to the carotid canal, anterolateral to the occipital condyle, and medial to the styloid process

Variants

• Several variations of the carotid artery within the temporal bone, such as a dehiscent carotid canal or aberrant carotid artery