Case of the Month: June, 2011, Page 2

Answer: Arnold Chiari Malformation Type 1. Also known as Chiari I Malformation

Imaging Findings:

  • Pointed cerebellar tonsils ≥ 5 mm below foramen magnum
  • (+/-) Syringohydromyelia (14-75%)
  • "Tight foramen magnum" with small/absent cisterns
  • (+/-) Elongation of fourth ventricle, hindbrain anomalies
  • Oblique tonsillar folia (like "sergeant's stripes")



Some people with Chiari-I have no symptoms. But in others, signs and symptoms may include:

  • Headaches, especially those brought on suddenly by coughing, sneezing or straining
  • Neck pain
  • Unsteady gait
  • Vomiting
  • Swallowing difficulties
  • Slurred speech

Because cerebrospinal fluid can't drain properly, excess fluid may build up in the brain (hydrocephalus). This usually requires the surgical placement of a shunt system to divert cerebrospinal fluid to another part of the body.

Overview Of Chiari Malformations:

  • Chiari I = downward displacement of  cerebellar tonsils below foramen magnum (>  5 mm); unrelated to Chiari II malformation.
  • Chiari II = abnormal neurulation leads to a small posterior fossa, caudal displacement of  brainstem and herniation of  tonsils and vermis through the foramen magnum; myelomeningocele.
  • Chiari III = encephalocele and Chiari II findings (rare). Chiari IV = severe cerebellar hypoplasia (rare).


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