I can see one or two things on your MRI. It is difficult to see where the lower edge of your cerebellar tonsils end, as the border is imprecise on the image and could in fact be lower down than it suggests, due to changes in signal seen at the two red dots. Do you have the images to each side of this ‘mid-sagittal’ one ?
There is a subtle sign of instability between C1 and C2 where the green V is, also the rear of your C1 encroaches a little into the spinal opening. I can see that you have a loss of lordosis (which is the term used for the natural ‘C’ shape) of the cervical spine. There is a larger than expected space between the spinous processes (jutty out bits of the back of the spine) where I’ve put the two blue dots, it’s called ‘fanning’ and this could have affected the disks between those cervical vertebrae.
Hope some of this is useful.