The procedure most commonly performed in patients with Chiari I Malformation is a posterior fossa decompression, which is accompanied by reconstruction: the dura is opened and grafted. The surgery is customized for each patient based on an analysis of the morphology (shape and form) of the skull, neurological tissues and the findings during surgery. Dr. Oró is a pioneer in performing the decompression surgery with reconstruction.
During surgery, the patient is asleep under general anesthesia. An area of hair about two inches wide is shaved at the back of the head. An incision is created from the occipital area at the back of the head to upper neck. Bone is removed at the base of the back of the skull and from the back part of the cervical one (C1) vertebrae. In rare case, the lamina (roof bone) of C2 is also removed.
Once the bone in this area is removed, a tough membrane, called the dura matter, is seen. Ultrasound is then performed (called color doppler-ultrasonography), to show the tonsils, the degree of crowding, and most importantly, the location of the blood vessels in the area. This helps guide the opening of the dura membrane.
Once the dura membrane is opened, the position of the tonsils and the degree of crowding is assessed. In patients with a syrinx, it is important to look between the tonsils and make sure that a drainage path for spinal fluid, the foramen of Magendie, is open. Sometimes a thin veil is found over the foramen that must be opened to free spinal fluid flow.
In some cases, marked crowding is present despite the opening of the dura. In these cases, the tips of the cerebellar tonsils are shrunk with electrocautery, which is applied with a fine pincer forceps. No specific side effects have been described from this shrinkage. The important point is to create more room in the area, remove the crowding, and allow for normal flow of spinal fluid.
Next, a patch of tissue is sewn to the edges of the open dura to enlarge the dural sac. The patch material, called pericranium, is tissue obtained from underneath the scalp in the area just above the bony removal.
Once the patch is sewn in, a customized titanium plate is attached to the edges of the bony resection by very small titanium screws. The plate, designed by Dr. Oró and produced by Biomet Microfixation, covers but does not compress the area of decompression. The muscles that were previously attached to the bone in this area can now be stitched to the plate. This union allows for natural reconstruction and helps avoid the sunken defect that some people develop after posterior fossa decompression surgery.
Lastly, the tissues are closed with stitches. Staples are used to close the skin.