Arnold-Chiari I malformation vs Arnold-Chiari II and Dandy-Walker malformations
How to tell Arnold-Chiari I malformation and Arnold-Chiari II and Dandy-Walker malformations apart when a board question makes them look alike.
Chiari I is tonsils in older patient; Chiari II is myelomeningocele infant; Dandy-Walker is cystic fourth ventricle/enlarged posterior fossa.
Side by side
Chiari I is cerebellar tonsil herniation through foramen magnum, often presenting later with headache, syringomyelia, or ataxia.
Chiari II has downward displacement of cerebellar vermis, tonsils, and medulla with myelomeningocele; Dandy-Walker has vermian agenesis, cystic fourth-ventricle dilation, and enlarged posterior fossa.
Chiari I is cerebellar tonsil herniation through foramen magnum, often presenting later with headache, syringomyelia, or ataxia.
Chiari II is hindbrain herniation tied to open spinal dysraphism, whereas Dandy-Walker is abnormal cerebellar vermis development with a large posterior fossa cyst.
The repair move
Before naming the answer, force the stem through the separator: Chiari I is tonsils in older patient; Chiari II is myelomeningocele infant; Dandy-Walker is cystic fourth ventricle/enlarged posterior fossa.
Try a free question
CoreA 28-year-old woman has progressive occipital headaches worsened by coughing and Valsalva maneuvers, with associated cerebellar signs, and a cape-like distribution loss of pain and temperature sensation across her shoulders. MRI shows the cerebellar tonsils extending 8 mm below the foramen magnum into the upper cervical canal, with a syringomyelia of the cervical cord. Which condition is most likely?
Show answer and explanation
Answer: A. Chiari I malformation. Chiari I malformation is cerebellar tonsil herniation through the foramen magnum without spinal dysraphism. Presents in older children or adults with cough/Valsalva-induced occipital headaches, cerebellar ataxia, and often syringomyelia (causing dissociated cape-like sensory loss). Treat with posterior fossa decompression.
Why the other choices are tempting
- B. Chiari II malformation is downward displacement of cerebellar vermis, tonsils, and medulla, associated with myelomeningocele in infants.
- C. Dandy-Walker malformation features vermian agenesis and cystic dilation of the fourth ventricle with enlarged posterior fossa.
- D. Posterior fossa tumor (medulloblastoma, astrocytoma) could compress the cerebellum but would show a mass on MRI, not just tonsillar herniation.
- E. Intracranial hypertension can cause headaches but does not classically produce tonsillar herniation with syrinx.
Flashcards
Tap a card to flip it.
What clue supports Arnold-Chiari I malformation?
Choose Arnold-Chiari I malformation when the stem gives this pattern: Chiari I is cerebellar tonsil herniation through foramen magnum, often presenting later with headache, syringomyelia, or ataxia.
What clue supports Arnold-Chiari II and Dandy-Walker malformations?
Choose Arnold-Chiari II and Dandy-Walker malformations when the stem gives this contrasting pattern: Chiari II has vermis/brainstem herniation with myelomeningocele and hydrocephalus; Dandy-Walker has cystic fourth ventricle dilation and enlarged posterior fossa.
Quick answers
What is the fastest way to tell Arnold-Chiari I malformation from Arnold-Chiari II and Dandy-Walker malformations?
Chiari I is tonsils in older patient; Chiari II is myelomeningocele infant; Dandy-Walker is cystic fourth ventricle/enlarged posterior fossa.
What is the key clue for Arnold-Chiari I malformation?
Chiari I is cerebellar tonsil herniation through foramen magnum, often presenting later with headache, syringomyelia, or ataxia.
What is the key clue for Arnold-Chiari II and Dandy-Walker malformations?
Chiari II has downward displacement of cerebellar vermis, tonsils, and medulla with myelomeningocele; Dandy-Walker has vermian agenesis, cystic fourth-ventricle dilation, and enlarged posterior fossa.