Just a quick response, I think you are right, you have very low-lying cerebellar tonsils (lowest part of hind brain) that are almost protruding through the foramen magnum (hole in the bottom of skull), sometimes referred to as ‘Chiari 0’. You also have a retroflexed odontoid (a backwards facing top of axis bone, the peg-like C2 vertebra bone). Either of these two elements can interfere with the normal flow of cerebro-spinal fluid, so the combination of these two elements, gives you a double whammy so to speak. If you are unfortunate enough to have EDS (or have suffered a head and neck injury which was bad enough to have torn the ligaments) this can cause instability around the cranio-cervical junction, giving you another contributing factor to the restriction of cerebro spinal fluid.