• Clinical science

Craniovertebral junction anomalies (Craniocervical junction anomalies)


The craniovertebral junction (CVJ) is composed of the occiput, the foramen magnum, and the first two cervical vertebrae, encompassing the medulla oblongata and the upper cervical spinal cord. Anomalies of the CVJ may be congenital or acquired. CVJ anomalies that decrease the volume of the posterior cranial fossa (e.g., platybasia) cause Chiari malformations, while erosion of the cervical vertebrae causes basilar invagination (cranial migration of the odontoid process), and anomalous fusion of the cervical vertebrae causes Klippel-Feil syndrome. Clinical features of CVJ anomalies are due to compression of the brain stem and the spinal cord and may include recurrent occipital headaches, neck aches, bulbar palsy, and upper and lower motor neuron palsy. CVJ anomalies can also obstruct the flow of CSF, resulting in syringomyelia and/or hydrocephalus. Diagnostics include neck x-ray and CT/MRI of the head and neck. Surgery is often indicated to prevent or treat neurological symptoms.


Basic anatomy

  • The CVJ is composed of the occiput, the foramen magnum, and the first two cervical vertebrae (the atlas, and the axis).
  • It encompasses and protects the medulla oblongata and the upper cervical spinal cord.



Chiari malformations

Type I CM

(Chiari I malformation)

Type II CM

(Arnold-Chiari malformation)


(Chiari III malformation)

Clinical features
CT/MRI of the brain
  • Caudal displacement of cerebellar tonsils (> 4 mm into the spinal canal)
  • Small posterior cranial fossa
  • Features of type I CM
  • In addition, caudal displacement of a beaked dorsal midbrain, and (possibly) the fourth ventricle
  • Features of type I CM
  • In addition, caudally displaced cerebellum and/or medulla protrude through an osseous defect in the skull (encephalocele)

  • Treatment
    • Surgery: indicated in all patients; with type II and III CM and in symptomatic type I CM
    • Surveillance: indicated in asymptomatic type I CM ; annual MRI of the brain to look for development of syringomyelia and/or hydrocephalus


Basilar invagination

  • Definition: abnormal protrusion of the odontoid process (dens) of the axis into the foramen magnum
  • Etiology: : CVJ abnormalities (mostly acquired CVJ)
  • Clinical features
  • Diagnostics
  • Treatment: surgery
    • Distraction of C1 and C2 vertebrae (with a spacer/rod), followed by occipitocervical fusion
    • To prevent further cranial migration of the odontoid process and neurological complications


Klippel-Feil syndrome (congenital synostosis of the cervical vertebrae)

  • Definition: congenital fusion of ≥ 2 cervical vertebrae
  • Etiology
  • Clinical features
    • Classic triad: short neck, restricted cervical mobility, and low posterior hair line
    • Hearing loss, genitourinary abnormalities, and cardiovascular abnormalities are also common.
  • Diagnostics
  • Treatment
    • Conservative; management (cervical collars/braces/traction): in mildly symptomatic patients without cervical spine instability
    • Surgery: indicated in patients with cervical spine instability or neurological symptoms
      • Posterior arthrodesis, stabilization of the C-spine, followed by immobilization in a halo cast or a neck brace