Location of the Foramen Spinosum
The foramen spinosum is located in the greater wing of the sphenoid bone (Alae majores). It can be observed from the cerebral surface (Facies cerebralis), facing the middle cranial fossa (Fossa cranii media), and at the external skull base (Basis cranii externa).
- On the cerebral surface, the foramen spinosum lies posterolateral to the foramen ovale. The foramen petrosum may sometimes be found between them.
- On the external skull base, the foramen is visible within the greater wing of the sphenoid bone. Nearby, on the infratemporal surface near the posterior border of the wing, lies the spine of the sphenoid (Spina ossis sphenoidalis).
Contents of the Foramen Spinosum
The foramen spinosum transmits the following structures:
- Middle meningeal artery (a. meningea media) — the largest branch supplying the dura mater. It is a branch of the first (mandibular) part of the maxillary artery (a. maxillaris). The artery ascends, passes through the foramen spinosum into the cranial cavity, and divides into frontal (r. frontalis) and parietal (r. parietalis) branches.
- Meningeal branch of the mandibular nerve (r. meningeus spinosus) — a branch of the trigeminal nerve. It branches off from the mandibular nerve inferior to the foramen ovale and enters the cranial cavity through the foramen spinosum alongside the middle meningeal artery.
- Emissary vein of the middle meningeal artery (middle meningeal vein).
Role in Blood Supply and Innervation
The middle meningeal artery passing through the foramen spinosum is the primary blood supply source for the dura mater. It has a large caliber because it nourishes not only the dura but also the cranial bones. Its vascular territory includes the entire lateral, convex surface of the cranial vault. It gives off branches to the tympanic cavity mucosa (a. tympanica superior), the canal for the greater petrosal nerve (r. petrosus), the orbit (r. orbitalis), and an anastomotic branch to the lacrimal artery (r. anastomoticus cum a. lacrimali).
The meningeal branch of the mandibular nerve provides sensory innervation to the dura mater of the middle cranial fossa.
Topography and Neighboring Structures
The foramen spinosum is one of the pathways connecting the middle cranial fossa to the external skull base. Additional openings in this fossa include the foramen ovale, carotid canal (Canalis caroticus), and foramen lacerum.
Externally, the skull base transitions laterally into the infratemporal fossa (Fossa infratemporalis). The middle meningeal artery branches off the maxillary artery between the neck of the mandibular condyle and the sphenomandibular ligament, then courses toward the foramen spinosum.