Hi and welcome to the Chiari forum.
As LCJ mentioned above, Chiari is a malformation of the skull, the part that holds the cerebellum. Because this area is too small, it can cause the cerebral tonsils to herniate out of the foreman magnum, this is the area where the brain stem and spinal cord come thru an opening of the skull to hold the skull on top of the spinal column.
With the herniation of the cerebral tonsils, this can cause compression of the brain stem, and obstruction of CSF flow.
As LCJ mentioned this causes many symptoms including pain....but many with obstructed CSF can also develop a syrinx, and other related conditions, like intercranial hypertension, POTS, disk issues, thyroid issues, joint pains due to Ehlers-danlos, RA, ot other connective tissue or auto immune disorders.
If u were dx'd with Chiari u want to educate urself, and then find a Dr that is a true Chiari specialist to help guide u as to ur best options.
Know u r not alone, we r here..ask and we will do our best to share what we have learned along our journey with Chiari.
A Chiari Malformation is a deformity in the base of the skull where the cerebellum meets the spinal column. It (typically) results in cerebellar tonsils which cause a compression on the spinal column, which in turn reults in pain, tightness headache etc.