There is little doubt that the MRI, and its cousin the cine MRI, are
the imaging tools of choice in diagnosing Chiari and syringomyelia. However, a group of
researchers from the Sanjay Gandhi Postgraduate Institute of Medical Sciences in India,
led by Dr. Arora, recently used a different technique to closely examine patterns of
cerebrospinal fluid flow in a group of patients with Chiari and syringomyelia. They
published their findings in the February, 2004 issue of the journal Acta Neurochirurgica.
Radionuclide cisternography involves injecting a tracer agent into the CSF system. As the tracer agent disperses, images taken at different times clearly show the where the tracer is, and thus reveal how the CSF is flowing. The research team used just such a technique on 17 patients they treated between 2000 - 2002.
The patient group included 13 men and 4 women with an average age 26. Each person had both a demonstrable Chiari and syrinx, and had endured their symptoms for between 2 months and 15 years. In addition to the radionuclide cisternography, each person also underwent standard X-rays and MRI's. As a group, the patients exhibited signs of pain, motor weakness, sensory disturbances, cranial nerve compression, cerebellar compression, and other symptoms typical of CM/SM (see Table 1).
Prior to treatment, each person was given a disability score using a modified scoring system. The researchers began with a system developed to measure disability due to spinal disease and added components specific to Chiari and SM. The final system had 8 categories: sensory, paresis, gait, urinary/bowel, muscle control in the arms/legs, neck pain, respiratory problems, and cranial nerve signs. The first four categories were scored 1-5, with a 5 representing no disability, and a 1 representing total disability. The latter categories were scored similarly, but with a range of 1-3. When combined, the total possible score, which represented no disability, was 32.
Also before surgery, each patient underwent the radionuclide cisternography. The tracer was injected into the lumbar region and an image was taken immediately after. Follow-up images were taken 1, 2, 4, 6, and 24 hours after the injection.
From these images, the researchers identified three categories of CSF flow, which they termed: rapid, delayed, and blocked. In the rapid group, which consisted of 7 patients, the tracer element quickly moved up the spinal cord and crossed the foramen magnum into the brain region in less than an hour. Here it quickly dispersed as it would in a healthy person.
In the delayed group, which also consisted of 7 patients, the tracer crossed the foramen magnum in the usual amount of time, but then it was delayed and took nearly 24 hours to disperse throughout the brain area. Finally, in the blocked group, which consisted of 3 patients, the tracer never crossed the foramen magnum, indicating that the CSF flow was completely blocked by the Chiari malformation.
All the patients underwent decompression surgery and then were reevaluated at follow-up (3 months to 1 year after surgery) using the disability scoring system. In addition, 10 patients underwent the radionuclide cisternography for a second time and 11 patients underwent a standard MRI.
Before the surgery, the patients in the rapid flow group had the highest average score on the disability scale (27 out of 32), meaning they were the least affected by the CM/SM (see Table 2). Both the delayed and blocked group of patients had lower scores, with the blocked group suffering the most (20 out of 32).
After surgery, the groups scored at about the same level, however the improvement in the blocked group was dramatically higher than the delayed and the rapid group. In fact, the patients in the rapid group only improved on average by 0.7 from before surgery, compared to an average increase of 8.3 in the blocked group.
The follow-up radionuclide cisternography showed that all 10 patients who took the test demonstrated normal CSF flow (they would be categorized as rapid). In addition, the MRI's showed that the syrinxes collapsed in 4 of the patients. It is also interesting to note that, as many previous studies have found, the amount of tonsillar herniation did not relate to either the type of CSF flow or the disability score before or after surgery.
In comments published in the same journal, Dr. Klekamp, a widely recognized syringomyelia expert, points out that this study highlights that patients with CM/SM are not all the same and that this imaging technique identified three distinct types of flow. He also points out, however, that he would not classify the rapid group as having normal flow, since the Chiari malformation essentially guarantees an abnormal flow.
While the radionuclide cisternography is a useful research technique, it is probably not practical for clinical purposes given its invasiveness. The MRI - both static and cine - will likely remain the imaging workhorse in the world of Chiari for the foreseeable future. Still, it is interesting that this study revealed a group of people for whom the surgery did not significantly improve things, and the patients in the group were the ones who were the best off before surgery.
-- Rick Labuda