Clinical Uses
The most significant impact of magnetic resonance neurography is on the evaluation of the large proximal nerve elements such as the brachial plexus (the nerves between the cervical spine and the underarm that innervate shoulder, arm and hand), the lumbosacral plexus (nerves between the lumbosacral spine and legs), the sciatic nerve in the pelvis, as well as other nerves such as the pudendal nerve that follow deep or complex courses.
Neurography has also been helpful for improving image diagnosis in spine disorders. It can help identify which spinal nerve is actually irritated as a supplement to routine spinal MRI. Standard spinal MRI only demonstrates the anatomy and numerous disk bulges, bone spurs or stenoses that may or may not actually cause nerve impingement symptoms.
Many nerves, such as the median and ulnar nerve in the arm or the tibial nerve in the tarsal tunnel, are just below the skin surface and can be tested for pathology with electromyography, but this technique has always been difficult to apply for deep proximal nerves. Magnetic resonance neurography has greatly expanded the efficacy of nerve diagnosis by allowing uniform evaluation of virtually any nerve in the body.
There are numerous reports dealing with specialized uses of magnetic resonance neurography for nerve pathology such as cervical radiculopathy, guidance for nerve blocks, demonstration of cysts in nerves, carpal tunnel syndrome, and obstetrical brachial plexus palsy. In addition several formal large scale outcome trials carried out with high quality "Class A" methodology have been published that have verified the clinical efficacy and validity of MR Neurography.
Use of magnetic resonance neurography is increasing in neurology and neurosurgery as the implications of its value in diagnosing various causes of sciatica becomes more widespread. There are 1.5 million lumbar MRI scans performed in the US each year for sciatica, leading to surgery for a herniated disk in about 300,000 patients per year. Of these, about 100,000 surgeries fail. Therefore there is successful treatment for sciatica in just 200,000 and failure of diagnosis or treatment in up to 1.3 million annually in the US alone. The success rate of the paradigm of lumbar MRI and disk resection for treatment of sciatica is therefore about 15%(Filler 2005). Neurography has been applied increasingly to evaluate the distal nerve roots, lumbo-sacral plexus and proximal sciatic nerve in the pelvis and thigh to find other causes of sciatica. It is increasingly important for brachial plexus imaging and for the diagnosis of thoracic outlet syndrome. Research and development in the clinical use of diagnostic neurography has taken place at Johns Hopkins, the Mayo Clinic, UCLA, UCSF, Harvard, the University of Washington in Seattle, University of London, and Oxford University (see references below) as well as through the Neurography Institute. Recent patent litigation concerning MR Neurography has led some unlicensed centers to discontinue offering the technique. Courses have been offered for radiologists at the annual meetings of the Radiological Society of North America (RSNA), and at the International Society for Magnetic Resonance in Medicine and for surgeons at the annual meetings of the American Association of Neurological Surgeons and the Congress of Neurological Surgeons. The use of imaging for diagnosis of nerve disorders represents a change from the way most physicians were trained to practice over the past several decades, as older routine tests fail to identify the diagnosis for nerve related disorders. The New England Journal of Medicine in July 2009 published a report on whole body neurography using a diffusion based neurography technique. In 2010, RadioGraphics - a publication of the Radiological Society of North America that serves to provide continuing medical education to radiologists - published an article series taking the position that Neurography has an important role in the evaluation of entrapment neuropathies.
Magnetic resonance neurography does not pose any diagnostic disadvantage relative to standard magnetic resonance imaging because neurography studies typically include high resolution standard MRI image series for anatomical reference along with the neurographic sequences. However, the patient will generally have a slightly longer time in the scanner compared to a routine MRI scan. Magnetic resonance neurography can only be performed in 1.5 tesla and 3 tesla cylindrical type scanners and can't really be done effectively in lower power "open" MR scanners - this can pose significant challenges for claustrophobic patients. Although it has been in use for fifteen years and is the subject of more than 150 research publications, most insurance companies still classify this test as experimental and may decline reimbursement, resulting in the need to file appeals. Patients in some plans obtain standard insurance coverage for this widely used procedure.
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