The human skull acts as a protective casing for the brain, but it is not a solid structure. Instead, it features numerous natural openings, known as foramina. These foramina serve as vital passageways for crucial structures like nerves and blood vessels to connect the brain and other internal skull components with the rest of the body. Their presence is essential for the proper functioning and communication of the central nervous system and its associated structures.
Locating the Foramen Spinosum
The foramen spinosum is a small opening situated within the greater wing of the sphenoid bone. This bone forms a significant portion of the skull’s base. The foramen spinosum is found posterolateral to another prominent opening called the foramen ovale.
When viewed from the base of the skull, this foramen is bordered posteriorly and laterally by the spine of the sphenoid bone. Its size is quite small, with an average adult diameter around 2.63 mm. It is located between 3 and 4 mm away from the foramen ovale in adults.
Structures Passing Through the Foramen Spinosum
Two structures pass through the foramen spinosum: the middle meningeal artery and the meningeal branch of the mandibular nerve. The middle meningeal artery originates from the maxillary artery, a branch of the external carotid artery. Once inside the skull, it supplies oxygenated blood to the dura mater, the tough outer membrane that envelops the brain, and also provides blood to the inner surfaces of the cranial bones.
The middle meningeal artery divides into anterior and posterior branches that spread over the dura mater, forming characteristic grooves on the inner surface of the skull. The meningeal branch of the mandibular nerve, sometimes referred to as the nervus spinosus, also passes through. This small sensory nerve branch originates from the mandibular division of the trigeminal nerve (Cranial Nerve V). Its function is to provide sensory innervation to the dura mater within the middle cranial fossa.
Clinical Relevance
The structures that pass through the foramen spinosum are clinically important, particularly the middle meningeal artery. This artery is vulnerable to injury from head trauma, especially temporal bone fractures. A common injury site is the pterion, a weak point on the side of the skull where several bones meet. Damage to the middle meningeal artery can lead to an epidural hematoma.
An epidural hematoma is a rapid collection of blood between the dura mater and the inner surface of the skull. Because the bleeding is arterial and under high pressure, blood accumulates swiftly, compressing the brain. Symptoms may include severe headache, nausea, vomiting, confusion, and a fluctuating level of consciousness, sometimes with a brief period of lucidity before a decline. This medical emergency requires immediate diagnosis and often surgical intervention to relieve pressure and prevent severe neurological damage or death.