- Protrusion of tonsils > 5 mm below foramen magnum
- Tonsils are sharp and pointed inferiorly
- Fourth ventricle is slightly low in position
- Tonsil descent may cause mild medullary compression
- Cervical cord syrinx may be seen
- Tectal plate is normal
- Corpus callosum is normal
Hofkes, Shawn K., et al. “Differentiation between symptomatic Chiari I malformation and asymptomatic tonsilar ectopia by using cerebrospinal fluid flow imaging: initial estimate of imaging accuracy.” Radiology 245.2 (2007): 532-540.