Craniovertebral junction anomalies

Last updated: September 21, 2022

Summary

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.

Overview

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.

Etiology

Congenital anomalies of the CVJ
- Occiput: condylar hypoplasia, fusion of the atlas to the occiput (atlantooccipital assimilation), platybasia (abnormal flattening of the base skull)
- Atlas: atlantooccipital assimilation, atlantoaxial fusion, aplasia of the arches
- Axis: hypoplasia of the odontoid process (dens)
Acquired anomalies of the CVJ
- Trauma: to the bones or the supporting ligaments of the CVJ
- Inflammatory: rheumatoid arthritis, ankylosing spondylitis
- Genetic syndromes: Down syndrome, achondroplasia, osteogenesis imperfecta
- Malignancies: chondrosarcoma, multiple myeloma, metastatic deposits

References:^[1]

Chiari malformations

Definition: : caudal displacement of the cerebellum with/without the medulla oblongata, through the foramen magnum, due to CVJ anomalies
Epidemiology
- Incidence: Type I Chiari malformation is the most common anomaly; 1 in 1,000 live births
- Sex: ♀ > ♂
Associations
Pathophysiology: multiple theories
- Fluid theory: neural tube defect → cerebrospinal fluid leakage → decreased volume of the posterior cranial fossa → compression and downward displacement of the cerebellum with/without the medulla oblongata through the foramen magnum
- Molecular genetic theory: congenital defects of the posterior brain and bony structures
- Growth abnormality theory: poorly coordinated cranial and cervical growth
- Crowding theory: small posterior cranial fossa → crowding of neural tissue at the foramen magnum
Clinical features and diagnostics

Clinical features and diagnostics of Chiari malformations
	Type I CM (Chiari I malformation)	Type II CM (Arnold-Chiari malformation)	Type III CM (Chiari III malformation)
Definition	Ectopic extension of cerebellar tonsils through the foramen magnum	Protrusion of cerebellar tonsils, vermis, and medulla oblongata into the foramen magnum	Herniation of parts of the cerebellum and brain stem through an abnormal opening in the back of the skull (encephalocele)
Clinical features	Usually symptomatic in adolescence/young adulthood: Occipital headache (exacerbated by valsalva maneuvers and physical activity) Neck pain Radicular pain in the shoulders and arms Lower cranial nerve disorders Cerebellar symptoms (e.g., dysarthria, ataxia) Downbeat nystagmus: the eyes pathologically drift upwards followed by a quick downward saccade Some patients develop syringomyelia and/or hydrocephalus.	Usually symptomatic in infancy Obstructive hydrocephalus: Displacement of brain tissue into the foramen magnum results in stenosis of the cerebral aqueduct Breathing difficulties, including apneic episodes Feeding difficulties Muscle weakness or numbness Always associated with myelomeningocele: manifests with motor and/or sensory deficits at and below the level of the lesion Some patients develop syringomyelia	Mostly fatal in early infancy For those that survive: Upper and lower motor neuron palsies Cranial nerve disorders Cerebellar symptoms Epilepsy Intellectual disability
CT/MRI of the brain	Caudal displacement of cerebellar tonsils 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

Chiari malformations Noncommunicating hydrocephalus Chiari I malformation Herniation of cerebral tonsils in Chiari I malformation Chiari II malformation

References:^[2]^[3]^[4]

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
- Recurrent occipital headache, neck pain
- Breathing difficulties, including sleep apnea
- Bulbar palsy
- Downbeat nystagmus
- Commonly associated with Chiari malformations, hydrocephalus, and/or syringomyelia
Diagnostics
- Neck x-ray (lateral view): protrusion of the odontoid process by ≥ 3 mm above of Chamberlain line
- CT: confirm x-ray findings
- MRI: indicated in patients with neurological symptoms; can demonstrate brainstem/spinal cord compression, hydrocephalus or syringomyelia, if present
Treatment: surgery

References:^[5]^[6]^[7]^[8]

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

Definition: congenital fusion of ≥ 2 cervical vertebrae
Etiology
- Genetic mutation (sporadic/inherited)
- Associated with Chiari malformations, scoliosis, spina bifida occulta, or Sprengel deformity (a congenitally elevated scapula)
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
- Cervical spine x-ray (AP and lateral views): cervical vertebral fusion; scoliosis, Sprengel deformity and spina bifida, if present can be seen on x-rays
- CT: useful in planning surgery
- MRI: indicated in patients with neurological symptoms/deficits; can demonstrate cord compression and/or Chiari malformation, if present
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

References:^[9]

References

Chiari Malformations. https://rarediseases.org/rare-diseases/chiari-malformations/. Updated: January 1, 2014. Accessed: April 10, 2017.
Williams H. A unifying hypothesis for hydrocephalus, Chiari malformation, syringomyelia, anencephaly and spina bifida.. Cerebrospinal Fluid Res. 2008; 5: p.7.doi: 10.1186/1743-8454-5-7 . | Open in Read by QxMD
Chiari Malformation Fact Sheet. https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Chiari-Malformation-Fact-Sheet. Updated: March 13, 2020. Accessed: March 25, 2021.
Klippel-Feil Syndrome. https://rarediseases.org/rare-diseases/klippel-feil-syndrome/. Updated: January 1, 2016. Accessed: April 10, 2017.
Atlanto-axial Impaction (Basilar Invagination). http://www.wheelessonline.com/ortho/atlanto_axial_impaction_basilar_invagniation. Updated: April 11, 2012. Accessed: April 10, 2017.
Joaquim AF, Ghizoni E, Giacomini LA, Tedeschi H, Patel AA. Basilar invagination: Surgical results. J Craniovertebr Junction Spine. 2014; 5 (2): p.78-84.doi: 10.4103/0974-8237.139202 . | Open in Read by QxMD
Smith JS, Shaffrey CI, Abel MF, Menezes AH. Basilar invagination. Neurosurgery. 2010; 66 (3 Suppl): p.39-47.doi: 10.1227/01.NEU.0000365770.10690.6F . | Open in Read by QxMD
Chamberlain Line on Radiographic Image. http://www.ebmconsult.com/articles/chamberlain-line. Updated: June 1, 2015. Accessed: April 10, 2017.
Lumenta CB, Di Rocco C, Haase J, Mooij JJA. Neurosurgery. Springer ; 2009

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