foramen spinosum

**Location:** Greater wing of the sphenoid, posterolateral to the foramen ovale. It opens from the middle cranial fossa into the infratemporal fossa.

**Contents:** - Middle meningeal artery (MMA), a branch of the maxillary artery (from the external carotid) - Middle meningeal vein (accompanying vein) - Meningeal branch of CN V3 (nervus spinosus), which re-enters the skull and supplies the dura mater

**Mnemonic for the middle cranial fossa foramina (anterior to posterior):** "Some Say Marry Money, But My Brother Says Big Brains Matter More" - Superior orbital fissure → CN III, IV, V1, VI, ophthalmic veins - Foramen rotundum → CN V2 - Foramen ovale → CN V3, accessory meningeal artery, lesser petrosal nerve (variable), emissary veins - Foramen spinosum → middle meningeal artery and vein, meningeal branch of V3 - Foramen lacerum → internal carotid passes over it (not through). The nerve of the pterygoid canal passes through it.

**Clinical significance:** - **Epidural hematoma:** The MMA runs just deep to the pterion, the thin junction of the frontal, parietal, temporal, and sphenoid bones. A temporal bone fracture here can tear the MMA. Arterial bleeding strips the dura from the skull, producing a lens-shaped (biconvex) hematoma on CT that does not cross suture lines. Classically there is a brief loss of consciousness, then a lucid interval, then rapid deterioration. Uncal herniation can follow, causing CN III compression ("blown pupil") and a contralateral hemiparesis. Treatment is emergent surgical evacuation. - **Contrast with subdural hematoma:** This is a bridging vein tear. It is crescent-shaped and crosses sutures but not the midline. It is common in the elderly and in alcoholics. - **Referred pain:** The meningeal branch of V3 supplies the dura, so dural irritation can contribute to headache. - **Embryology and anatomy:** The MMA arises from the first part (mandibular) of the maxillary artery. It passes between the two roots of the auriculotemporal nerve. - **Variants:** The foramen may be absent or incomplete, or it may merge with the foramen ovale. The MMA is then transmitted through the foramen ovale or elsewhere. This is rare and is relevant to skull base surgery and imaging.

**High-yield pearl:** On boards, "lucid interval + lens-shaped hematoma + temporal bone fracture" should make you think of the MMA, which enters the skull via the foramen spinosum.