Craniotomy vs Craniectomy

July 31st, 2009 -- While the goals of Chiari surgery are straightforward - to create more space around the cerebellar tonsils and restore the natural flow of cerebrospinal fluid - the devil is in the details. Currently, there are a number of open issues when it comes to the specific techniques involved, such as how much bone to remove, whether to open the dura, whether to remove any brain tissue, and what type of dural patch to use. With all these options, for patients it can seem like no two surgeons perform the surgery the same way.

The reality is that the procedure for Chiari surgery is still evolving, with surgeons exploring new variations ranging from minor tweaks like how to open the dura, to fundamental changes like bone only decompressions. The existence of these variations is not necessarily a bad thing, since the failure rate for Chiari surgery is still relatively high at around 20%. However, there is a real problem in the lack of methodologically sound clinical trials to compare the effectiveness of different techniques and approaches.

Right now, when a surgeon develops a new Chiari technique they will publish their results on a series of patients. Other surgeons may then comment on the technique and point out what they like or don't like about the approach. For minor issues this is not a big deal, but for large controversies, the lack of sound data leaves patients without recourse in evaluating what is best for them.

Highlighting the evolving nature of Chiari surgery, a group of surgeons from UCLA recently published a technical note in the journal, Child's Nervous System, where they describe using craiotomies instead of craniectomies for Chiari surgery. A craniectomy is where a piece of the skull is removed to gain access to the brain. With a craniotomy, a piece of the skull is also removed to gain access, but it is then put back into place at the end of the procedure.

While most surgeries at the back of the skull utilize a craniotomy, because the goal of Chiari surgery is to create more space, traditionally surgeons do not replace the piece of bone. However, research not specific to Chiari has shown that craniectomies in general can lead to post-operative headaches because the muscles in the neck attach directly to the dura. When these muscles tighten, it can pull on the dura.

Although some surgeons now use a metal plate to take the place of the bone flap that was removed, the UCLA surgeons believed that replacing the bone itself would be preferable. In order to ensure that there was enough space around the cerebellar tonsils, the surgeons used a plate to elevate the bone flap above where it used to be (Figure 1).


cranio1.jpg

Figure 1: Surgical Picture Showing Bone Flap with Plate Attached

The doctors reported their results with this technique on six pediatric patients (Table 1). In all six cases, there was a significant improvement in the quality of life and in the two children who had syrinxes, both resolved completely. The doctors also showed, using MRIs, that putting the bone back still increased the size of the posterior fossa.

This provides another interesting alternative for Chiari surgeons to consider. In order to make informed decisions, one would hope that randomized, controlled trials comparing craniectomy to craniotomy for Chiari surgery will be undertaken soon.


Table 1: Pre and Post-Op Posterior Fossa Volume (cc) of Six Chiari Patients Who Underwent Craniotomy

Age Sex Pre-Op PFV Post-Op PFV
17 F 170 180
18 M 187 198
13 F 172 203
4 M 144 183
14 M 155 177
6 F 181 197

Note: Volumes are measured in cubic centimeters (cc)


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Study Compares Surgical Techniques