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As stated earlier, there is an expected failure rate of up to 30 percent with these various techniques. Consequently, there has been a recent trend toward simultaneous treatment of the Chiari malformation and its associated anomalies such as hydromyelia. Some advocate plugging of the congenital inlet (the obex) to the spinal cord's central fluid canal to prevent the ingress of fluid. This is based on a feeling that the fluid found within the syrinx arises within the brain and is sucked or pushed through the obex and central fluid canal of the spinal cord to reach the syrinx. Some advocate simple drainage of the cavity, feeling that the accumulation process is either static or that the mechanism driving the accumulation has been dealt with in dealing with the Chiari malformation. Others would argue that re-accumulation of the syrinx can occur and therefore a more permanent egress path should be established by placing a small tube into the cavity with the other end either resting in the fluid space outside the spinal cord or in some other body cavity to which the fluid can drain. Our bias has been to decompress the hind brain malformation by removing both the overlying bone and opening the soft tissue coverings (the dura). For Type I Chiari malformations, we remove the tissue that is hanging down and compressing the spinal cord (the cerebellar tonsils). We use an intraoperative ultrasound to image the interior of the cord. If the syrinx ascends to the level of the brain stem, the outlet of the fourth ventricle is inspected to ensure that it is open. If not, it is opened, and we sometimes lay a small tube through the outlet to prevent it from re-closing. A graft is then used to enlarge the dural sleeve investing the spinal cord. If the pre-operative MRI scans show the syrinx to be distended, consideration is given to treating the syrinx surgically.