Arnold Chiari Malformation

1. ACM I: tonsils only
2. ACM II: tonsils and brainstem + usually myelomeningocele
3. ACM III: herniation of cerebellum
4. ACM IV: severe hypoplasia of cerebellum without herniation

Arnold-Chiari malformation Type I

• usually occurs in adolescents without hydrocephalus; CMI is predominantly a congenital abnormality. Prior to MRI, CMI was observed almost exclusively in those aged 10-30 years, hence the term adult-type Chiari malformation.
• herniation of the cerebellar tonsils through the foramen magnum into the cervical spinal canal.
• cerebellar tonsils often are elongated and peglike.
• Mild caudal displacement and flattening or kinking of the medulla may be present.
• The vermis cerebelli and the fourth ventricle are normal or only minimally deformed.
• not directly associated with other congenital brain malformations, specifically myelomeningocele. (myelomeningocele is a feature of Chiari II malformation)
• However, craniovertebral malformations are common in patients with CMI.
• Distention with cerebrospinal fluid (CSF) of the central canal of spinal cord (ie, hydromyelia) or paracentral cavities (ie, syringomyelia) is present in approximately 25% of patients with CMI. The cervical cord is the most common site of syringohydromyelia.
• Symptoms:
  • Suboccipital headaches
  • Ocular symptoms, including retro-orbital pain, visual disturbances, photophobia, and diplopia
  • Otoneurologic symptoms, including dizziness, vertigo, hearing disturbances, oscillopsia, nystagmus, and synkinesis
  • Hindbrain compression symptoms, including weakness, paresthesia, ataxia, cranial nerve palsies, dysphagia, dysphasia, palpitations, syncope, apnea, and sudden death
  • Syringomyelia symptoms, including central cord syndrome, impaired sensation, impaired motor control, gait disturbance, torticollis, bowel and/or bladder symptoms, neuropathic joints, trophic phenomena, and pain
  • Spinal cord dysfunction, which is present in as many as 94% of patients with syringomyelia and 66% without syringomyelia

Arnold-Chiari malformation (Type II)

• hydrocephalus due to downward displacement of cerebellar tonsils and brainstem into cervical canal
• almost invariably associated with myelomeningocele
• remember Type I usually occurs in adolescents without hydrocephalus
• Presents with HA/neck pain/LE spasticity

Arnold-Chiari malformation (Type III)

• herniation of the cerebellum through the foramen magnum

Arnold-Chiari malformation (Type IV)

• severe cerebellar hypoplasia without displacement of brain through the foramen magnum

CHLA Board Review 2005
eMedicine.com Chiari I Malformation, Last Updated: August 11, 2005, Chiari II Malformation
Last Updated: November 15, 2002