ACR Codes: 1.1
Chiari Malformations (CM) are divided into 4 subtypes.
• CM - 1 is diagnosed by appropriate symptoms and low lying cerebellar tonsils (cerebellar tonsillar ectopia - tonsils > 5mm below foramen magnum). The phsyiology is not related to the degree of hernation, but rather to the CSF flow around the tonsils. Symptoms include:
» Decreased sensation/numbness in extremities
» Upper extremity pain, weakness
» Headache
» Tinnitus
» Decreased facial sensation (spinal portion of CNN V)
» Gait disorder, bowel/bladder Sx, Nystagmus
NOTE: Patients may be symptomatic with only 3mm of herniation; and, asymptomatic with up to 10 mm. Syringohydromyelia is associated in 20-25%.
• CM - 2 Is like CM-1, but includes a spinal dysraphism (myelomeningocele). This is the "Arnold-Chiari" malformation. The posterior fossa may be small, and both the cerebellum and 4th ventricle are herniated through the Foramen Magnum, usually with "kinking" of the medulla and/or cervical cord (up to 70%). These patients usually have a complex malformation including hydrocephalus, a "beaked" midbrain, callosal anomalies (up to 90%, such as agenesis of the rostrum and or splenium.
• CM - 3 Chiari III malformation is like a CM - 2, but includes a cervical/occipital encephalocele.
• CM - 4 Chiari IV is controversial and not accepted by all authors. It is a small or underdeveloped cerebellum.
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