Medical Device Daily Washington Editor

WASHINGTON — The 2007 meeting of the American Association of Neurological Surgeons (AANS; Rolling Meadows, Illinois) highlighted a tremendous number of advances in diagnostic and treatment modalities, and a number of sessions were dedicated to trigeminal neuralgia, a condition so severely painful that it is often referred to as the suicide disease.

Conventional surgery is one of the more common approaches to this condition along with pharmaceutical treatment, but surgeons are sometimes surprised at what they find when they arrive at the base of the brain, where the trigeminal nerves plug into the central nervous system. While magnetic resonance may seem arcane compared to positron emissions as a means of imaging nerve tissue, two researchers who presented this past Tuesday have found a way to merge magnetic resonance imaging with magnetic resonance angiography to render 3-dimensional images with the help of software plucked from the web at no cost.

Just as remarkable, one of the participants in this research is a resident, bolstering the notion that the best ideas often come from those who are just making their way into the field.

In the paper accompanying the presentation, Kim Burchiel, MD, of the Oregon Health and Science University (Portland, Oregon) and Jonathan Miller, MD, of Case Western Reserve University (Cleveland) wrote that their work allows a doctor to "objectively visualize the trigeminal nerve and nearby vessels at an unprecedented level of anatomic detail." After accepting the William Sweet Award for young investigators, Miller, a resident at University Hospitals (Cleveland) said that current imaging techniques "have been suboptimal mainly because of insufficient resolution."

Magnetic resonance gives good detail, Miller noted, but it cannot differentiate smaller structures from one another, a reference to the finer veins and arteries that populate the area near the brain stem, as well as some of the smaller nerves in the area.

Using the Achieva, a 3-tesla MRI machine manufactured by Philips Medical Systems (Bothell, Washington), the pair scanned a dozen patients who had reported symptoms suggestive of trigeminal neuralgia, ten of whom exhibited arterial or venous structures "identical in location and configuration to that predicted by preoperative analysis." One patient was said to have had a vein embedded in the trigeminal nerve, which was apparently not picked up by the scanning technique. No explanation for the outcome of the 12 patients was offered in the paper.

As is always the case when it comes to imaging technology, this technique has proved immensely valuable in dealing with patients. "It makes it much easier to explain what we'll be doing," Miller said, adding that the benefit for surgeons is that "in a way, you're seeing into the future."

The software that the team used to merge the scanning data into 3-dimensional images is OsiriX, an imaging program written for computers made by Apple (Cupertino, California) — which run on a UNIX-based operating system — and hence might not run on a Windows/Intel computer.

Miller noted that this technique could also be used to diagnose hemofacial spasm and glossopharyngeal neuralgia.

Hospital administrators and patients alike are unlikely to complain about the cost of the procedure, either. "The addition of the fast field images" to the angiography scan "is really negligible," Miller noted, adding that "we haven't had to charge patients any additional fees."

One member of the audience stated that while the imaging technique in question was useful, he remarked that "to use it as a diagnostic tool per se is a slippery slope," given the incidence of compressed arteries and veins at the stem of the brain that are incidental in nature and not associated with any disorder. Miller responded that the images are "primarily used as a regime to find out what we'll see intraoperatively" and not as a diagnostic tool other than to rule out compression.

Anyone who has suffered from trigeminal neuralgia can testify to the profound pain induced by the condition, which has been described as "the most excruciating pain known to humanity." The condition is rare relative to other disorders, with about 45,000 Americans diagnosed each year, and pharmaceutical treatments include gabapentin (Neurontin), which can induce an allergic reaction that closes off the throat.

Open surgery is another option, but even with sophisticated 3-D imaging, most doctors and patients would elect to avoid the knife.

Despite the dangers presented by possible ionization of nearby tissues, stereotactic radiosurgery is an alternative treatment for this disease. Researchers at the University of California at Los Angeles (UCLA) presented the results of a decade of stereotactic radiosurgery using ionizing radiation provided by a linear particle accelerator, and while their results suggest that radiation does not cure the condition, it does open a door to relief for older and more frail populations that might not tolerate either drugs or conventional surgery.

UCLA would have previously conducted such work with the Leksell Gamma Knife, but the institution discarded the Gamma Knife in 1997 in favor of the Novalis system, manufactured by BrainLAB (Munich, Germany). The Novalis system retains the stereotactic approach of using multiple sources of radiation that converge on the source of the problem and leave surrounding tissues undisturbed, but the Novalis system more effectively shapes the beams to the exact shape of the diseased tissue, which reduces even further the chances of damage to surrounding tissue. Another benefit is that many conditions can be treated in one session while other stereotactic approaches require multiple treatments, an approach known as fractionation.

Zachary Smith, MD, and his team at UCLA's department of neurosurgery treated 164 patients between 1995 and 2005, and keeping with the general age of occurrence of this condition, the average age was 65. The first 15 patients received a low dose of radiation (70 Gy) and a "30% isodose-line radiation at the brain stem." The straight radiation dose for another 69 patients was boosted to 90 Gy, with the same percentage reaching the brain stem. The final 23 patients received the same 90 Gy dose, but the dose reaching the stem went up to half the original dose level.

The results of 120 of the 164 patients showed that 82 had experienced "excellent/good pain relief" at a mean follow-up of 19 months, but the reports varied by the amount of dose hitting the brain stem. Of the 69 patients who received the 90 Gy/30% in-stem dose, 50 (72%) reported "significant relief." However, almost 45% experienced "subjective numbness." When the 90 Gy dose resulted in a 50% dose ratio at the stem, about 85% reported significant relief (23 of 27), with almost 78% experiencing generally mild numbness.

Smith remarked that radiosurgery is less risky than conventional surgery for elderly and otherwise frail patients, adding that a "larger brainstem dose may yield a higher degree of pain relief, but may lead to an increased rate of numbness."