Definition: caudal displacement of the cerebellum with/without the medulla oblongata, through the foramen magnum, due to CVJ anomalies

Type I CM (Chiari I malformation)

• 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
• Some patients develop syringomyelia and/or hydrocephalus.

Type II CM (Arnold-Chiari malformation)

• 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