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C2 Vertebra (Axis)

The C2 vertebra, also known as the axis, is the second cervical vertebra and a specialized vertebra that forms the pivot for rotation of the head and atlas (C1). Its defining feature is the odontoid process (dens), which projects superiorly to articulate with the anterior arch of the atlas.

The C2 vertebra is a critical structural and functional component of the upper cervical spine and is a key focus in trauma imaging, congenital anomalies, degenerative disease, and craniovertebral junction assessment.

Synonyms

  • Axis

  • Second cervical vertebra

Location

  • Second vertebra of the cervical spine

  • Inferior to the atlas (C1)

  • Superior to the C3 vertebra

  • Forms part of the craniovertebral junction

  • Situated posterior to the pharynx and anterior to the cervical spinal cord

Anatomical components

  • Vertebral body:

    • Supports the odontoid process

  • Odontoid process (dens):

    • Superior projection articulating with anterior arch of C1

    • Serves as the pivot for atlantoaxial rotation

  • Pedicles and laminae:

    • Form the vertebral arch

  • Spinous process:

    • Large, bifid, posterior projection

  • Superior articular facets:

    • Articulate with inferior facets of C1

  • Inferior articular facets:

    • Articulate with superior facets of C3

  • Transverse processes:

    • Contain transverse foramina for vertebral arteries

Relations

Anteriorly:

  • Pharynx and prevertebral soft tissues

  • Anterior longitudinal ligament

Posteriorly:

  • Spinal cord and posterior longitudinal ligament

  • Ligamentum flavum and posterior neck muscles

Superiorly:

  • Atlas (C1)

  • Anterior and posterior atlantoaxial joints

Inferiorly:

  • C3 vertebra and intervertebral disc

Laterally:

  • Transverse foramina and vertebral arteries

  • Paravertebral muscles

Ligamentous attachments

  • Transverse ligament of the atlas:

    • Stabilizes the dens against the anterior arch of C1

  • Alar ligaments:

    • Extend from dens to occipital condyles

  • Apical ligament:

    • Connects dens to the foramen magnum

  • Anterior and posterior longitudinal ligaments

X-ray appearance

Cervical spine radiographs (AP, lateral, open-mouth odontoid view):

  • Vertebral body: Rectangular outline with smooth cortical margins

  • Dens: Vertical midline projection clearly seen on open-mouth view

  • Atlantoaxial alignment: Symmetric lateral masses of C1 over C2

  • Spinous process: Prominent bifid posterior projection

CT appearance (pre-contrast)

Non-contrast CT:

  • Cortical bone: Hyperdense, sharply defined outer margins

  • Dens: Well-corticated odontoid process with smooth contours

  • Vertebral body and arches: Clearly delineated trabecular structure

  • Facet joints: Well-visualized articular surfaces

  • Transverse foramina: Round osseous canals bilaterally

  • Alignment: Precise assessment of atlantoaxial and C2–C3 alignment

MRI appearance

T1-weighted images:

  • Cortical bone: Low signal intensity

  • Bone marrow: Intermediate-to-high signal depending on age

  • Dens: Low-signal cortex with intermediate marrow signal

  • Intervertebral discs: Intermediate signal

T2-weighted images:

  • Bone marrow: Intermediate signal

  • CSF around spinal cord: High signal

  • Spinal cord: Homogeneous intermediate signal

  • Ligaments: Low signal linear structures

STIR:

  • Bone marrow: Normally suppressed fat signal

  • Ligaments and soft tissues: Low signal

  • Excellent for evaluating marrow and soft-tissue edema

CT image

C2 Vertebra (Axis) CT CORANAL Anatomy, Location and Imaging Appearance -img-00000-00000

CT image

C2 Vertebra (Axis) CT SAG Anatomy, Location and Imaging Appearance -img-00000-00000

X-Ray image

X Ray C2 Vertebra (Axis)

CT VRT 3D image

C2 Vertebra (Axis) 3D