Three structures pass through the foramen spinosum: the middle meningeal artery, the middle meningeal vein, and a small nerve called the nervus spinosus. This tiny circular opening sits in the greater wing of the sphenoid bone, near the base of the skull, and serves as a critical passageway connecting the outside of the skull to the interior cavity that houses the brain.
Where the Foramen Spinosum Is Located
The foramen spinosum sits in the greater wing of the sphenoid bone, a bony projection that forms part of the floor of the middle cranial fossa (the bowl-shaped area that supports the temporal lobes of the brain). It gets its name from its position near the spinous process of the sphenoid, a small bony point that juts downward from the skull base.
Its nearest neighbor is the foramen ovale, a larger opening that carries the mandibular branch of the trigeminal nerve out of the skull. The two foramina are only about 3 to 4 millimeters apart, with the foramen spinosum sitting just behind and to the side of the foramen ovale. This tight spacing makes the area especially important during skull base surgery, where the foramen spinosum serves as a reliable landmark for locating surrounding nerves and blood vessels.
The Middle Meningeal Artery
The most clinically important structure passing through the foramen spinosum is the middle meningeal artery. This artery branches off the maxillary artery (a major blood vessel in the face and jaw region), travels upward, and enters the skull through the foramen spinosum. Once inside, it runs along the inner surface of the skull and supplies blood to the dura mater, the tough protective membrane that lines the inside of the skull and surrounds the brain.
The middle meningeal artery is the primary blood supply to the dura in the middle and anterior parts of the skull. It runs alongside paired veins, and because it sits so close to the inner surface of the temporal bone (one of the thinnest parts of the skull), it is vulnerable to injury from head trauma.
The Middle Meningeal Vein
Running alongside the artery, the middle meningeal vein (sometimes referred to as veins, since they often travel as a pair) drains blood from the dura mater back out through the foramen spinosum. These veins follow roughly the same path as the artery but carry blood in the opposite direction, moving it away from the brain’s covering and back toward the deeper venous networks outside the skull.
The Nervus Spinosus
The third and smallest structure through the foramen spinosum is the nervus spinosus, also called the meningeal branch of the mandibular nerve. This nerve has an unusual path: the mandibular nerve first exits the skull through the nearby foramen ovale, then gives off this small branch, which loops back and re-enters the skull through the foramen spinosum. Once inside, the nervus spinosus provides sensory innervation to the dura mater, meaning it carries pain and pressure signals from the brain’s protective lining.
Why the Middle Meningeal Artery Matters in Head Injuries
The clinical significance of the foramen spinosum centers largely on the middle meningeal artery and what happens when it tears. A blow to the side of the head can fracture the thin temporal bone and lacerate the artery, causing an epidural hematoma: a life-threatening collection of blood that builds up between the skull and the dura mater. Because the bleeding is arterial, pressure accumulates rapidly, compressing brain tissue underneath.
Epidural hematomas most commonly form in the temporoparietal region, exactly where the middle meningeal artery runs. On imaging, they appear as a lens-shaped collection of blood pressing inward against the brain. During surgical repair, bleeding from the foramen spinosum itself sometimes needs to be plugged with bone wax to stop the flow at its source. A traumatic tear in this area can also create an abnormal connection between the artery and its paired veins, a condition known as an arteriovenous fistula.
Anatomical Variations
The foramen spinosum is not identical from person to person. It varies in shape, size, and even whether it is present at all. In some individuals, the foramen is incomplete or absent on one side, which means the middle meningeal artery may enter the skull through a different route, sometimes sharing the foramen ovale instead. These variations matter for surgeons and radiologists interpreting imaging of the skull base.
During fetal development, the foramen spinosum forms as bony processes of the sphenoid gradually fuse around the artery and nerve passing through. This process begins around 8 to 10 weeks of gestation, when membranous bone starts forming near the area. The sphenoid spine, the bony point adjacent to the foramen, completes its formation late in fetal development and varies considerably between individuals. These developmental differences explain why the foramen’s final shape and size are so variable in adults.
The Foramen Spinosum as a Surgical Landmark
Because the foramen spinosum is easy to identify during surgery, it serves as a reference point for locating other structures in the middle cranial fossa. Surgeons operating in this region use it to orient themselves relative to the mandibular nerve (just a few millimeters away at the foramen ovale), the greater superficial petrosal nerve, and the internal carotid artery where it passes through the petrous bone. Knowing the typical distances and anatomical relationships around the foramen spinosum helps surgeons preserve these critical structures during procedures on the skull base.