Mastoid emissary foramen

Where is the mastoid foramen located?

Mastoid foramen (foramen mastoideum) is located on the temporal bone, on its petrous part (pars petrosa), in the region of the prominent mastoid process (processus mastoideus). The mastoid process is directed posteriorly and laterally and is bounded by the occipital border (margo occipitalis).

The mastoid foramen connects the sulcus for the sigmoid sinus (sulcus sinus sigmoidei) with the external surface of the mastoid process.

The mastoid foramen is one of the communications between the posterior cranial fossa (fossa cranii posterior) and the external cranial base. The posterior cranial fossa is bounded anteriorly by the superior border of the petrous part (margo superior partis petrosae) and the dorsum sellae (dorsum sellae), and posteriorly by the cruciform eminence (eminentia cruciformis) and the sulcus for the transverse sinus (sulcus sinus transversi).

The external cranial base (basis cranii externa) is viewed from the inferior, basal aspect. The mastoid foramen is among the foramina and canals visible on the external cranial base.

What passes through the mastoid foramen?

The following structures pass through the foramen mastoideum:

• Emissary vein. Emissary veins also pass through the parietal and condylar foramina.
• Mastoid branch (r. mastoideus), a branch of the occipital artery (a. occipitalis), passing through the mastoid foramen into the dura mater.

The occipital artery arises at the level of the posterior belly of the digastric muscle (m. digastricus) and runs posteriorly beneath the muscles of the occiput. It gives off sternocleidomastoid branches (rr. sternocleidomastoidei), an auricular branch (r. auricularis) to the posterior surface of the auricle, terminal occipital branches (rr. occipitales) to the skin and muscles of the occiput, and a meningeal branch (r. meningeus), which enters the cranium through the parietal foramen.

Topography and adjacent structures

The following structures are located on the mastoid process:

• Mastoid notch (incisura mastoidea).
• Groove for the occipital artery (sulcus arteriae occipitalis).
• Sulcus for the sigmoid sinus (sulcus sinus sigmoidei), communicating with the external surface via the mastoid foramen.

Anterior to the mastoid process is the styloid process (processus styloideus). Between the styloid and mastoid processes lies the stylomastoid foramen (foramen stylomastoideum), which is the outlet of the facial canal (canalis nervi facialis).

On the inferior surface of the petrous part of the temporal bone there are also the jugular notch (incisura jugularis) with the intrajugular process (processus intrajugularis), jugular fossa (fossa jugularis), external aperture of the carotid canal (apertura externa canalis carotici), and the aperture of the cochlear canaliculus (apertura canaliculi cochleae). Between the temporal and occipital bones lie the jugular foramen (foramen jugulare) and the petrooccipital fissure (fissura petrooccipitalis).

Class and exam questions

What else to study on this topic

• Posterior cranial fossa (fossa cranii posterior)
• External cranial base (basis cranii externa)
• Occipital artery (a. occipitalis)
• Temporal bone (os temporale)

Other topics in the "Anatomical Structures" section

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.