MR Neurography an Emerging Modality in Musculoskeletal Pain

In a few short years, MR neurography—a fairly new imaging technique for the direct imaging of spinal and peripheral nerves—has emerged as an exciting new modality in pain detection and management.

By Mike Bassett

The subject of a Tuesday refresher course, MR neurography has "emerged as the poster child for innovation in the area of musculoskeletal pain and is one of the leading developments in our subspecialty over the last four or five years," said Sandip Biswal, M.D., an associate professor of radiology at the Stanford University Medical Center, who presented a session on "PET and MR Methods to Image Pain."

Sandip Biswal, M.D.

Chronic pain is now affecting approximately 116 million American adults and results in hundreds of billions of dollars annually in treatment costs and lost productivity, said Dr. Biswal. For example, according to a report issued by the Institute of Medicine in 2011, the annual cost of chronic pain in the U.S. is estimated to be $560-635 billion, including health care expenses and lost productivity—more than the annual costs associated with heart disease, cancer, and diabetes combined.

But the "ugly truth,' Dr. Biswal said, is that the conventional methods of finding pain generators are "just not adequate," which is one of the reasons why MR neurography is generating so much interest.

According to Amelie Lutz, M.D., a colleague of Dr. Biswal who presented the session, "MR Neurography of the Brachial Plexus and Upper Extremities," with improved scanner and coil techniques, and advances in pulse sequences, "we are now capable of directly imaging nerves with a very high resolution. This has become a really exciting—and evolving—field in radiology."

What MR neurophraphy does is "to really lay out the nerve beautifully," Dr. Biswal said. "We can reconstruct these images in a variety of dimensions or even trace them like we do with the vascular system. You can really lay out a pretty looking nerve and see if anything looks like a mass or inflammation, whether there are neuromas in it, or areas of clumping with the nerve root or intrinsic pathology in the nerve, rather than something compressing it."

MR Neurography Breaks Ground with Brachial Plexus

In her presentation, Dr. Lutz discussed the anatomy and normal MR imaging appearance of the brachial plexus and upper extremity nerves and how to recognize the most commonly encountered pathologies and their differential diagnoses in these regions.

"With the more central or proximal nerves like the brachial plexus it can be very challenging for physicians to really nail down the specific location and problem with nerve conduction studies or electromyographies," Dr. Lutz said. "The brachial plexus is probably one of the first areas in which people focus on this type of imaging."

And while the complexity of this anatomic region can appear "daunting," she said, with the proper tools to systematically analyze and break down anatomy "then suddenly it all makes sense."

Dr. Biswal discussed a number of new approaches to imaging pain involving PET and MRI. He is currently working on developing a biomarker that targets and helps measure the mechanisms of pain at the molecular level. "This PET tracer looks for markers of inflamed nerves," he said. "So whether it's increased ion channels in that nerve or increased pain receptors, or increased cellularity, that's what we're trying to mark." That, combined with MR techniques, will provide both a molecular readout along with an anatomic readout that will identify where pain is originating "with great specificity and sensitivity," Dr. Biswal said.

"Basically, what we are all doing is responding to that fact that conventional approaches to imaging pain just haven't been very good," said Dr. Biswal. One example of that has been the use of MR and CT to image patients with non-specific back pain.

A number of medical organizations have issued recommendations advising against lumbar MRI, mainly because it has not been very predictive or helpful in the acute setting, Dr. Biswal said.

Ultimately, Dr. Biswal said, improving ways to use imaging to find the source of pain will not only help patients by improving outcomes, but will serve to improve their quality of life. "We probably all have friends or relatives who are in chronic pain, and they get labeled as crazy or depressed, and it turns out that patients who have chronic pain are unfortunately difficult to deal with," he said. "Something like this can dominate their existence and we can help them on the route to recovery."

Tuesday's session also covered, "MR Neurography of the Lumbar Plexus and Lower Extremities" by presenter Avneesh Chhabra, M.D., who discussed current state-of-the-art techniques available for LS plexus evaluation and shared normal and abnormal imaging appearances of various common and uncommon pathologic states involving LS plexus and its branch nerves. The talk also addressed new 3D techniques that suppress vessel signal effectively while preserving effective nerve visualization.

The session, "DTI of the Peripheral Nervous System," presented by Gustav Andreisek, M.D., covered the basic principles of diffusion-tensor imaging (DTI), the challenges and limitations for imaging protocols, as well as the evaluation of DTI images quantitatively and qualitatively.

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