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Craniovertebral junction anomalies

Last updated: February 19, 2020


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



Chiari malformations

Type I CM

(Chiari I malformation)

Type II CM

(Arnold-Chiari malformation)


(Chiari III malformation)

Clinical features
CT/MRI of the brain

  • 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


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



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