Hello, i did a brain mri today and got this: incidental low-lying cerebellar tonsils extending approximately 4-5 mm inferior to the foramen magnum bilaterally. does it means i have arnold chiari malformation? what is the treatment for it?

Yes, like about 1/100 people. In the absence of any related symptoms, the management is usually limited to monitoring over time. If there are symptoms, other options are available.

If this is clinically asymptomatic and not causing demonstrable objective abnormalities, there is no indicated necessary intervention. Observation over time should suffice.