Which of the following statements regarding Chiari type I malformation is correct?
- A It is invariably associated with a lumbar myelomeningocele
- B It is characterized by caudal displacement of the brainstem, fourth ventricle, and inferior vermis through the foramen magnum
- C It is defined by herniation of cerebellar tonsils more than 5 mm below the foramen magnum in adults, often with a pointed tonsillar tip ✓
- D The fourth ventricle is displaced into the cervical spinal canal
Correct answer: C. It is defined by herniation of cerebellar tonsils more than 5 mm below the foramen magnum in adults, often with a pointed tonsillar tip
Explanation
Chiari I malformation consists of peg-like, pointed cerebellar tonsils extending more than 5 mm below the basion-opisthion line in adults, commonly associated with syringomyelia. Option B describes Chiari II, in which the vermis, brainstem, and fourth ventricle all descend and a myelomeningocele is essentially always present. In Chiari I the fourth ventricle remains in its normal position, which distinguishes it from Chiari II and III.
Reference: Osborn's Brain: Imaging, Pathology, and Anatomy, 2nd ed.
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Written and medically reviewed by the StethoPrep medical team.