Where is the mastoid foramen located?
The mastoid foramen (foramen mastoideum) is located on the temporal bone, within its petrous part (pars petrosa), specifically in the region of the prominent mastoid process (processus mastoideus). The mastoid process projects posterosuperiorly and is bounded by the occipital margin (margo occipitalis).
The mastoid foramen connects the sigmoid sinus sulcus (sulcus sinus sigmoidei) with the external surface of the mastoid process.
The mastoid foramen represents 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, and posteriorly by the cruciate eminence (eminentia cruciformis) and the transverse sinus sulcus (sulcus sinus transversi).
The external cranial base (basis cranii externa) is viewed from the inferior, basal norm. The mastoid foramen is among the apertures and canals visible on the external skull base.
What passes through the mastoid foramen?
The structures passing through the foramen mastoideum include:
- Emissary vein (mastoid 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 to the dura mater.
The occipital artery originates at the level of the posterior belly of the digastric muscle (m. digastricus) and courses posteriorly beneath the suboccipital muscles. It gives off sternocleidomastoid branches (rr. sternocleidomastoidei), an auricular branch (r. auricularis) to the posterior auricle, terminal occipital branches (rr. occipitales) to the scalp and muscles of the occiput, and a meningeal branch (r. meningeus), which enters the cranial cavity via the parietal foramen.
Topography and Neighboring Structures
The mastoid process features:
- Mastoid notch (incisura mastoidea).
- Occipital artery sulcus (sulcus arteriae occipitalis).
- Sigmoid sinus sulcus (sulcus sinus sigmoidei), which communicates 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 serves as the exit of the facial nerve canal (canalis nervi facialis).
On the inferior surface of the temporal bone pyramid, one also finds the jugular notch (incisura jugularis) with the intrajugular process (processus intrajugularis), the jugular fossa (fossa jugularis), the 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 petro-occipital fissure (fissura petrooccipitalis).