Chiari 1.5 and an Acquired Chiari DO NOT have the same meaning and therefore it is incorrect to use the words synonymously. However, when the brainstem is herniated along with the cerebellar tonsils (Chiari 1.5), it is a good indication that an Acquired Chiari exists and that there is another pathological cofactor to the Chiari that needs to be found and treated BEFORE DECOMPRESSION. There are pathological cofactors that are less likely to herniate the brainstem or that only herniate the brainstem over a course of time, so pathological cofactors should be checked even if you have a Chiari 1 malformation.

If our doctors looked for and addressed these co-factors prior to decompression, the number of failed decompressions and post-operative brain sags would significantly decline.

For more information on Chiari Types (including Chiari 1.5 and Acquired Chiari):
https://chiaribridges.org/chiari-malformation/

For more information on cofactors pathological to Chiari: https://chiaribridges.org/overview-chiari-comorbidities-etiological-pathological-cofactors/