Intraoperative Ultrasound May Not Be Effective

July 31, 2008 -- For several years now many surgeons have been using a type of imaging known as intraoperative ultrasound to determine whether it is necessary to open the dura during surgery. However, a recent study from Johns Hopkins (McGirt et al.) and published in the July, 2008 issue of the Journal of Neurosurgery: Pediatrics shows that ultrasound may not be reliable in determining whether a duraplasty is required.

As reported numerous times in this publication (including in this issue), there is an ongoing debate in the surgical community about whether and when to open the dura as part of Chiari surgery. Some surgeons, especially pediatric ones, have recently begun performing what are called bone only decompressions on selected patients. The major advantage of removing only bone and not opening the dura is that it dramatically reduces CSF related complications and in general is a less traumatic procedure. The drawback is that in some cases it may not be sufficient and a full duraplasty may be required in a follow-up procedure. Even the advocates of bone only decompression admit that patient selection is the key to success with the less invasive procedure, however objective guidelines for finding good candidates have failed to materialize.

That is why some surgeons have turned to using ultrasound, which can provide images using sound waves, during surgery to make the decision on whether to open the dura. Now the study from Hopkins calls into question the effectiveness of this practice. Specifically, the researchers looked at the rate of symptom persistence and recurrence in 256 pediatric Chiari cases treated surgically over a ten year period. The average age of the patients was 10 years and 47% were boys. Twenty-seven percent had syringomyelia and 11% had scoliosis. The extent of each patient's tonsillar herniation was classified as follows (note this has nothing to do with their symptom severity):

  • Mild = Below the foramen magnum but above C1

  • Moderate = Between C1 -C2

  • Severe = C2 and below

Using this criteria, the vast majority of the cases had moderate herniation (76%, Figure 1).

The decision on whether to recommend surgery was based on the imaging and whether patients had symptoms commonly associated with Chiari, such as headaches and brainstem related problems. In general, cases with very mild herniations and symptoms which were vague were discouraged from having surgery.

Three surgeons performed similar procedures on all the patients. Ultrasound was used to visualize the space around the tonsils and it was left to each surgeon's discretion whether to open the dura as part of the procedure. Overall, duraplasty was performed 55% of the time (140 patients). The group was followed for an average of 29 months and tracked for symptom persistence and/or recurrence.

As a group, symptoms resolved 78% of the time and persisted or recurred 22% of the time. In nineteen children (7%), the symptoms were severe enough to require additional surgery. When the researchers compared the duraplasty patients to the bone only patients, they found that for moderate and severe herniations, patients who had a bone only decompression were twice as likely to experience symptom recurrence. In other words, for herniations at the C1 level and beyond, the intraoperative ultrasound did not seem to do a good job in indicating whether the dura should be opened. However for mild herniations, the ultrasound appeared to be adequate.

An accompanying Editorial points out several limitations of this study which the authors readily acknowledge. Specifically, that the selection of patients for surgery in the beginning was subjective, that the interpretation of the ultrasound results during surgery was subjective, and that the outcome assessments are based on patient self-reports. Interestingly, the Editor calls for something that Conquer Chiari has begun pushing for in the research community, namely a validated assessment measure of the severity of Chiari symptoms and/or a quantitative MRI measurement which correlates with symptom severity. In addition, the Editor makes a general call, which Conquer Chiari wholeheartedly supports, for greater scientific rigor in the structure and methods of Chiari research.

On the positive side, McGirt and his colleagues have begun using what can be called actuarial reporting of their outcome data (which the journal Editor applauded). This style of data report shows the patient outcomes over the entire time period of follow-up rather than just at one or two points in time. What it also shows is something many Chiari patients know first-hand, that while they may feel better right after surgery, in a significant number of cases, symptoms start to come back over time.

Figure 1: Extent of Tonsillar Herniation (256 Patients)

Extent of Herniation Number of Patients Percent
FM - C1 38 15%
C1-C2 195 76%
Below C2 23 9%

Notes: FM = foramen magnum; C1 = first cervical vertebra, C2 = second cervical vertebra

Related C&S News Articles:

Ultrasound Can Determine Extent Of Surgery Necessary

Study Shows Promise For Conservative Surgery In Adults

New Dural Patch Found To Be Safe And Effective

Limited Surgery Shown To Be Effective In Children

To Open or Not To Open The Dura; That Is The Question