First let us review a normal diagram of the brain, cerebellum and spinal cord. You can see that the opening in the skull for the exit of the spinal cord is not that much larger then the spinal cord itself. This opening is called the foramen magnum.
In Chiari Malformations an excess of cerebellar tissue known as the cerebellar tonsils extends down through the foramen magnum into the upper portion of the spinal canal. In so doing, the cerebellar tonsils put pressure on the brain stem and spinal cord. This can lead to neurologic symptoms as well as to the formation of a syrinx .
In order to reduce the crowding at the foramen magnum, both bone and membranes must be removed. The proposed skin incision is shown, as well as the bone at the base of the skull which is to be removed. In addition, the posterior portions of the uppermost vertebra must be removed down to the level of the bottom of the cerebellar tonsils.
Once the bone has been removed, the membranes overlying the cerebellum and spinal cord should be opened. This membrane known as the dura encloses the entire central nervous system.
While there is much debate, most surgeons will choose to patch some type of membrane into the opening in the dura to create a large spinal fluid filled space behind the cerebellum, brain stem and spinal cord. The incision is then closed in several layers and the operation complete.
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