Jugular foramen

The jugular foramen is the cranial foramen located posterior to the carotid canal, formed by the petrous temporal bone and occipital bone where the sigmoid sinus and inferior petrosal sinus drain into the internal jugular vein and where cranial nerves IX–XI (glossopharyngeal, vagus, and accessory) exit ⁵. Ascending occipital and pharyngeal arteries are also located in this foramen ⁵.

Gross anatomy

Divisions: 2-part classification

The jugular foramen is commonly described in two parts, separated by a fibrous septum or a bony septum called the jugular spine (intrajugular processes on the opposing surfaces of the temporal and occipital bones):

• pars nervosa: anteromedial and smaller

• pars vascularis: posterolateral and larger

This nomenclature is misleading because both compartments contain vascular and neural structures.

Pars nervosa

The pars nervosa is the anteromedial portion of the jugular foramen and is smaller than the larger, posterolateral pars vascularis. It contains:

• inferior petrosal sinus

• glossopharyngeal cranial nerve (CN IX)

The 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.

The glossopharyngeal nerve yields a tympanic branch (Jacobson nerve) which 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.

Pars vascularis

The pars vascularis is the posterolateral portion of the jugular foramen and is larger than the smaller anteromedial portion termed the pars nervosa. It contains:

• jugular bulb: a venous expansion sitting in the jugular fossa, between the endocranial sigmoid sinus and the exocranial jugular vein

• vagus nerve (CN X)

• spinal accessory nerve (CN XI)

The vagus nerve yields 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.

Divisions: 3-part classification

In this system, the foramen is divided into 3 parts, 2 venous and 1 neural ^3,4:

1. petrosal part: anteromedial, passes the inferior petrosal sinus

2. intrajugular part: between the venous compartments and around the intrajugular processes, passes the glossopharyngeal nerve (anterolateral) and vagus and accessory nerve complex (posteromedial)

3. sigmoid part: posterolateral, passes the sigmoid sinus

Radiographic features

The size of the normal jugular foramen is remarkably variable and asymmetrical. However, the normal foramen will always be well-corticated. Therefore, the bony margin (and not the size) of the foramen should guide diagnostic evaluation.

CT

CT appearance of the foramen depends upon the level and angulation of the scan. The foramen has been described as having the shape of a sitting duck on the highest axial cuts.