Does a nerve pass between the skull and the C1 (cervical 1) vertebra?

Cranial Nerves Passing Between the Skull and C1 Vertebra

Yes, several cranial nerves pass between the skull and the C1 (atlas) vertebra, specifically cranial nerves IX (glossopharyngeal), X (vagus), XI (accessory), and XII (hypoglossal). 1

Anatomical Relationships

The cranial nerves that pass between the skull and C1 vertebra exit through specific foramina:

1. Glossopharyngeal (CN IX), Vagus (CN X), and Accessory (CN XI) nerves:

   • Exit through the jugular foramen
   • The jugular foramen is located at the base of the skull between the temporal bone and occipital bone
   • These nerves travel in close proximity within the carotid space after exiting 1

2. Hypoglossal nerve (CN XII):

   • Exits through the hypoglossal canal
   • The hypoglossal canal is located in the occipital bone near the foramen magnum
   • After exiting, it travels caudally within the carotid space 1

3. Spinal component of CN XI:

   • The spinal accessory nerve has a unique course
   • It originates from the ventral horn of the spinal cord between C1 and C5 levels
   • Ascends through the foramen magnum into the skull
   • Then exits with the cranial portion through the jugular foramen 1

Clinical Significance

This anatomical arrangement has important clinical implications:

• Fractures and trauma: Injuries to the craniocervical junction can damage these nerves, causing various cranial neuropathies

  • Jefferson (C1) fractures can result in impairment of CN IX and X, causing dysphagia 2
  • Occipital condyle fractures can lead to hypoglossal nerve injury 3

• Vascular pathology: The vertebral arteries also pass through this region

  • The V3 segment of the vertebral artery extends from the C2 transverse foramen, across the posterior arch of C1, and into the foramen magnum 1
  • Vertebral artery dissection can cause CN XII palsy or multiple cranial neuropathies 1

• Joint innervation: A previously undescribed branch from the hypoglossal nerve joins with branches from C1 and C2 nerves to form a plexus that innervates the atlanto-occipital joint 4

Imaging Considerations

When evaluating pathology in this region:

• MRI is the preferred imaging modality for evaluating cranial nerve pathology 1, 5

  • 3T MRI provides superior resolution for visualizing cranial nerves
  • Thin-section imaging with high spatial resolution is required
  • Pre- and post-contrast imaging provides the best opportunity to identify lesions

• CT is valuable for evaluating:

  • Temporal bone fractures
  • Bony anatomy prior to surgical intervention
  • Foraminal expansion or bone erosion 5

Important Anatomical Variations

• Vertebral artery variations are common in the upper cervical spine
  • In 1% of subjects, the vertebral artery courses medially over the lateral quarter of the C1/C2 joint surface 6
  • These variations are important to consider during procedures targeting the upper cervical spine

Understanding this complex anatomy is essential for proper clinical localization of lesions and for the selection of appropriate imaging protocols when evaluating patients with suspected cranial neuropathies.