Craniovertebral 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.

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]

• 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
  • Neural tube defects (esp. meningomyelocele)
  • Syringomyelia
  • Hydrocephalus
  • Klippel-Feil syndrome
  • Basilar invagination
• 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

• 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

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

• 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]

• 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]