Foramen Magnum: The Spinal Cord's Passage from Brain to Body | Anatomy

The foramen magnum (Latin: "great hole") is the large oval opening in the occipital bone at the skull base.

Structures Passing Through

• Medulla oblongata (continuous with spinal cord)
• Vertebral arteries (→ basilar artery → circle of Willis)
• Spinal accessory nerve (CN XI) (spinal rootlets)
• Meninges (dura, arachnoid, pia)
• CSF (subarachnoid space continuity)
• Anterior/posterior spinal arteries

Clinical Significance

• Foramen Magnum Syndrome: Compression (tumor, Chiari malformation, basilar invagination) → neck pain, weakness, sensory loss, autonomic dysfunction.
• Tonsillar Herniation (Chiari I): Cerebellar tonsils descend >5 mm → CSF obstruction, syrinx.
• Trauma: Occipital condyle fractures, atlanto-occipital dislocation.
• Surgical Access: Transcondylar, far-lateral approaches for ventral brainstem lesions.

The foramen magnum is the critical transition zone between brain and spinal cord.