Online Module: Chiari Malformations

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Online ModuleChiari Malformations
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About the term

• To say Chiari malformations is slightly
  misleading. The Chiari malformations actually
  consist of four defined types of hindbrain
  abnormalities, each distinct from the others.
• The first two types, especially type 1, will be
  briefly reviewed here. The 3rd and 4th types of
  Chiari malformations are exceedingly rare and
  will only briefly be mentioned.

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The Chiari Malformation

• The term usually refers to Type 1 Chiari
  Malformation, which is classically described as
  adult-onset Chiari (avg. age of presentation is
  40 yrs) with downward displacement of the
  cerebellar tonsils through the foramen magnum.
• Although this is a common radiographic feature of
  the condition, it is not a prerequisite for
  diagnosis.

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Type 1 Chiari

• Most common presenting complaint is suboccipital
  headache
• Neck pain, subjective weakness, numbness, loss of
  temperature sensation also 40-60 incidence
• Most common presenting sign is hyperactive lower
  extremity reflexes
• Cape-like sensory loss, nystagmus (downbeat),
  gait disturbance, upper extremity weakness, etc.,
  are also all very common (30-50 incidence of
  each).

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Type 1 Chiari why should you care?

• Patients who are identified early and receive
  early treatment have the best response to
  surgical intervention. Because of the variable
  constellation of signs and symptoms associated
  with type 1 Chiari, it is regularly missed or
  misdiagnosed.

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Type 1 Chiari - imaging

• MRI is diagnostic test of choice
• Can show compression of brain stem at foramen
  magnum (common, and significant finding)
• Hydrocephalus can be present
• Syringomyelia
• Descent of cerebellar tonsils through foramen
  magnum
• Importance probably related to brainstem
  compression at foramen magnum nevertheless, this
  is classic finding associated with type 1 Chiari.

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Type 1 Chiari malformation

• T1 weighted MRI w/o contrast, sagittal view in
  this outstanding picture of a patient with type 1
  Chiari, you see
• (1) cerebellar tonsils well below the foramen
  magnum
• (2) syringomyelia
• (3) compression of brainstem

(3)?
?(1)
(2)?
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Type 1 Chiari cerebellar tonsils

• The cerebellar tonsils normally ascend as we age
  in normal adults, the tonsils usually do not
  descend through the foramen magnum (or descend a
  very small amount), but in Chiari 1 patients
  descent is the norm. Lack of tonsillar descent
  is an extremely sensitive marker therefore, in a
  patient with presentation that can be consistent
  with type 1 Chiari and cerebellar tonsil
  protrusion through the foramen magnum gt 3mm, the
  pt. needs neurosurgery referral.

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Operative Results

• The most commonly-performed surgery is
  suboccipital craniectomy (essentially opens up
  the foramen magnum), with or without C1
  laminectomy and dural graft patch.
• Patients with pain as primary complaint respond
  best to surgery weakness less responsive, but
  overall 80 of patients report favorable
  results.
• Presence of muscle atrophy, ataxia, and duration
  of symptoms gt2 yrs all associated with poorer
  outcome.

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Type 2 Chiari

• Type 2 Chiari malformation is also referred to as
  Arnold-Chiari malformation.
• Presents in childhood
• Usually the younger it presents, the more severe
  the condition.
• Usually associated with myelomeningocele!!! (The
  USMLE loves this)

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Arnold-Chiari malformation

• Signs/symptoms secondary to brainstem and lower
  cranial nerve dysfunction.
• Findings (best seen on MRI)
• Caudal displacement of posterior fossa
  structures, including cervicomedullary junction,
  pons, medulla, 4th ventricle, and cerebellar
  tonsils. Classically, the cervicomedullary
  junction is described as having a kink-like
  deformity.

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Arnold-Chiari malformation

• Associated findings
• Hydrocephalus (VERY common requires shunt)
• Syringomyelia
• Agenesis/dysgenesis of corpus callosum
• Operative goals similar to type 1, but these
  patients do not do as well (and the younger their
  presentation, the worse the general outcome).

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Others

• Type 3 Chiari - Rare and severe (usually not
  compatible with life) basically, posterior fossa
  structures end up everywhere except where they
  should be.
• Type 4 Chiari Cerebellar hypoplasia without
  herniation.

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Summary

• For USMLE purposes, its good to understand the
  major characteristics of and differences between
  type 1 Chiari and type 2 Chiari, as it seems to
  show up a lot (probably because people mix them
  up a lot).
• Understand that type 1 Chiari malformation has an
  extremely variable presentation. If you keep it
  on your radar in patients who present with these
  symptoms, you can be a patients hero!