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Diagnosing Chiari Malformation
The 2021 Chiari and Syringomyelia Consensus stated the following for the diagnostic criteria for Chiari.
-One or both cerebellar tonsils descending caudally measured via the basion-opisthion line associated with small posterior fossa, on a midline sagittal T1 MRI:
<3mm - Normal
3-5mm - considered pathological if associated with a cervical syrinx and/or the cerebellar tonsils are peg-like.
5+mm - Chiari
Magnetic Resonance Imaging
MRIs use magnets and radio waves to create detailed images (they use no radiation). This is a safe and painless test. It shows detailed images of the brain and other parts of the body. Allowing the radiologist to assess where the cerebellar tonsils lie, the size of the posterior fossa, and other potential issues like Syringomyelia.
The best view when investigating Chiari is a brain MRI (as seen on the right), an image
the craniocervical junction can also allow for a good view of the cerebellum.
MRI machines can have different strengths which impact their quality, these appear like 2T or 3T on their advertising. With the higher number denoting a stronger magnet and better quality. To learn more about MRI go to our MRI page.
Specialised imaging they can do is called a CINE MRI. This will show how the CSF is flowing and show any areas of blockage. This can be helpful when surgeons are questioning performing surgery. It is NOT always required as some cases show obvious blockage in standard images.
Sometimes Chiari can be diagnosed via Computerized Tomography (CT), but a negative test does not rule out Chiari.
CT's uses x-ray scans to obtain cross-sections of the body. CT's expose the patient
to radiation. So are used sparingly. As MRI's show a much clearer image when
assessing Chiari it is preferred over CT's.
CT of Craniocervical Junction
MRI of Brain
The most accurate way to diagnose Chiari Malformation is via Magnetic Resonance Imaging (MRI).
Other tests/information your doctors may require include:
- Medical History
- Physical Exam
- Neurological Examination
These are used to assess if/how the chiari malformation is impacting the body.
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