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Chiari Malformations

Chiari I: Protrusion of the cerebellar tonsils below the foramen magnum (small posterior fossa, normal size cerebellum). Associated with Syringomyelia in 20%, Klippel-Feil syndrome in 10%. MRI: Peg-like tonsills > 5 cm below the foramen magnum, syrinx, abnormal cine CSF flow at craniocervical junction. Treatment: Suboccipital craniectomy and C1 laminectomy. Chiari II (Arnold-Chiari): Prenatal imaging: 100% associated with lumbosacral myelomenigocele, diagnosed as soon as 10 weeks by US. Lemon sign (Lemon shaped skull - bifrontal inward convexity). Banana sign (compressed cerebellum)

Postnatal imaging: Craniocaudally:
  1. Interdigitation of cerebral gyri
  2. Hydrocephalus
  3. Colpocephaly: teardrop shaped lateral ventricles
  4. Dysgenesis of Corpus Callosum
  5. Beaked tectum
  6. Towering cerebellum where the cerebellar tonsils wrap around the medulla
  7. Elongation of the 4th ventricle
  8. Elongation of the pons
  9. Small posterior fossa forcing content down the cervical spinal canal
  10. Scalloping of the clivus

Chiari III

High cervical or low occipital Meningoencephalocele + Chiari II (dx by single shot fast spin echo SSFSE MR)


Chiari IV

Myelomeningocele with Severe cerebellar hypoplasia