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Magnetic Resonance Neurography

Number: 0387



Policy

Aetna considers magnetic resonance neurography experimental and investigational because the medical literature on the application of this technology in clinical situations remains in early stages of development.

Background

Currently, diagnosis and management of nerve injury due to compression or trauma are generally undertaken without images of the nerves themselves.  Although nerves can sometimes be seen in standard magnetic resonance imaging (MRI), the method is so unreliable that nerve images have never played a significant role in diagnosis and clinical usefulness.  Magnetic resonance neurography is a new MRI technology requiring special software and hardware upgrades, which are not widely available; currently, this test is only available at a very limited number of medical centers.

Magnetic resonance neurography is capable of generating high resolution longitudinal and cross-sectional images of major peripheral nerves, and has been studied to supplement diagnostic evaluations by electromyography (EMG) and nerve conduction studies in patients with suspected peripheral nerve tumors, traumatic injury, post-irradiation neuritis, chronic compression, and pain syndromes where an anatomic lesion is suspected.  Although current evidence supports MR neurography as a promising technique, the outcome data that would determine the efficacy of this technology is limited to studies involving a small number of patients, making it premature to offer conclusions regarding its effectiveness for the general population.  Additionally, large-scale, well-conducted, controlled studies with this approach are warranted to determine its efficacy in imaging neurofibromas and distinguishing benign from malignant lesions.

In a prospective observational study of patients with sciatica, Zhang and colleagues (2009) investigated the effectiveness of three-dimensional (3-D) high-spatial resolution diffusion-weighted MR neurography based on steady state free precession (3-D diffusion-weighted steady-state free precession [DW-SSFP]) in the diagnosis of sciatica.  The 3-D DW-SSFP sequence was performed on 137 patients with sciatica and 32 patients in control group.  The post-processing techniques were used to generate images of lumbo-sacral plexus and sciatic nerve, and the images acquired were assessed based on the presence or absence of nerve abnormality.  The certainty of identifying the lumbo-sacral plexus and main branches from all cases was determined in each of the reconstruction planes for each case individually and assessed by using a 3-score scale.  The sciatic nerve and its main branches were differentiated and a clear picture was obtained in all subjects.  Compared with the control group, the presence of nerve root compression or increased T2 signal intensity changes can be observed in all patients.  The mean score of certainty of identifying the sciatic nerve and main branches was 1.76 +/- 0.4, which indicates that the sciatic nerve and main branches can be identified with certainty.  The authors concluded that the 3-D DW-SSFP MR neurography with high spatial and sufficient contrast is an excellent technique to define the nature of sciatica and assists in prognostication and possibly in management.

Du et al (2010) analyzed the role of MR neurography in the evaluation of spinal and peripheral nerve lesions.  Imaging studies, medical records, and EMG/nerve conduction studies (NCS) results were analyzed retrospectively in a consecutive series of 191 patients who underwent MR neurography for spinal and peripheral nerve disorders; 91 (47.6 %) of these patients also underwent EMG/NCS studies.  In those who underwent both MR neurography and EMG/NCS, MR neurography provided the same or additional diagnostic information in 32 % and 45 % of patients, respectively.  Magnetic resonance neurograms were obtained at a median of 12 months after the onset of symptoms.  The utility of MR neurography correlated with the interval between the onset of symptoms to MR neurography.  Twelve patients underwent repeated MR neurography for serial evaluation.  The decrease in abnormal signal detected on subsequent MR neurography correlated with time from onset of symptoms and the time interval between MR neurography, but not with resolution of symptoms.  Twenty-one patients underwent MR neurography post-operatively to assess persistent, recurrent, or new symptoms; of these 3 (14.3 %) required a subsequent surgery.  The authors concluded that MR neurography is a valuable adjunct to conventional MRI and EMG/NCS in the evaluation and localization of nerve root, brachial plexus, and peripheral nerve lesions.  They found that MR neurography is indicated in patients: (i) in whom EMG and traditional MR imaging are inconclusive; (ii) who present with brachial plexopathy who have previously received radiation therapy to the brachial plexus region; (iii) who present with brachial plexopathy and have systemic tumors; and (iv) in patients under consideration for surgery for peripheral nerve lesions or after trauma.  The authors also noted that MR neurography is limited by the size of the nerve trunk imaged and the timing of the study.

In a review on new approaches in imaging of the brachial plexus, Vargas et al (2010) stated that imaging plays an essential role for the detection and analysis of pathologic conditions of the brachial plexus.  Currently, several new techniques are used in addition to conventional 2-D MR sequences to study the brachial plexus: the 3-D STIR SPACE sequence, 3-D heavily T2w MR myelography sequences (balanced SSFP=CISS 3-D, True FISP 3-D, bFFE and FIESTA), and the diffusion-weighted (DW) neurography sequence with fiber tracking reconstruction (tractography).  The 3-D STIR sequence offers complete anatomical coverage of the brachial plexus and the ability to slice through the volume helps to analyze fiber course modification and structure alteration.  It allows precise assessment of distortion, compression and interruption of post-ganglionic nerve fibers thanks to the capability of performing maximum intensity projections (MIP) and multi-planar reconstructions (MPRs).  The CISS 3D, b-SSFP sequences allow good visualization of nerve roots within the spinal canal and may be used for MR myelography in traumatic plexus injuries.  The DW neurography sequence with tractography is still a work in progress, able to demonstrate nerves tracts, their structure alteration or deformation due to pathologic processes surrounding or located along the post-ganglionic brachial plexus.  It may become a precious tool for the understanding of the underlying molecular pathophysiologic mechanisms in diseases affecting the brachial plexus and may play a role for surgical planning procedures in the near future.

Eguchi et al (2011) stated that DW imaging (DWI) can provide valuable structural information that may be useful for evaluating pathological changes of the lumbar nerve root.  Diffusion-weighted MR neurography has recently been introduced as an alternative way to visualize nerves, but to date, quantitative DWI and MR neurography have not been applied to evaluate the pathology of lumbar nerve roots.  These researchers visualized lumbar nerve roots and analyzed their morphology by MR neurography, and measured the apparent diffusion coefficient (ADC) of lumbar nerve roots compressed by herniated disks using 1.5-T MR imaging.  A total of 10 consecutive patients (median age of  48.0 and range of 20 to 72 years) with mono-radicular symptoms caused by a lumbar herniated disk and 14 healthy volunteers were studied.  Regions of interests (ROIs) were placed on the lumbar roots at dorsal root ganglia (DRG) and distal spinal nerves on DWI to quantify mean ADC values.  The spinal nerve roots were also visualized by MR neurography.  In the patients, mean ADC values were significantly greater in the compressed DRG and distal spinal nerves than in intact nerves.  Magnetic resonance neurography also showed abnormalities such as nerve swelling at and below the compression in the symptomatic nerve root.  Increased ADC values were considered to be because of edema and Wallerian degeneration of compressed nerve roots.  The authors concluded that DWI is a potential tool for analysis of the pathophysiology of lumbar nerve roots compressed by herniated disks.

Merlini et al (2011) assessed the feasibility of MR neurography in children, and the potential roles of DWI and fiber-tracking (FT) techniques.  A total of 5 pediatric patients (age range of 6 to12 years) underwent MRI for various clinical indications: neurogenic bladder (case 1); persistent hand pain following minor trauma (case 2); progressive atrophy of the lower left extremity muscles (case 3); bilateral hip pain (case 4); and palpable left supraclavicular mass (case 5).  All studies were performed using a 1.5-T Avanto MRI scanner.  The protocol included 3D T2-weighted STIR and SPACE imaging, T1-weighted fat-saturation post-gadolinium imaging and diffusion tensor imaging (DTI) with tractography.  ADC (N×10(-3) mm(2)/s) and FA values were calculated from ROIs centered on the nerves.  Nerve-fiber tracks were calculated using a 4th-order Runge-Kutta algorithm (NeuroD software).  Magnetic resonance neurography allowed satisfactory visualization of all neural structures, and FA and ADC measurements were feasible.  The final diagnoses were Tarlov cysts, median-nerve compression, sciatic perineurioma, Charcot-Marie-Tooth disease and plexiform neurofibroma in a patient with NF-1.  The authors noted that measurements of FA and ADC are of little value because of the lack of normal reference values.  Nerve-fiber tractography (FT) may be of value in the characterization of tumor pathology, and is also helpful in the planning of surgical treatments.  They concluded that MR neurography is feasible in pediatric patients.  However, a considerable amount of work has yet to be done to establish its role in the clinical management of the wide range of peripheral nerve diseases.

The Work Loss Data Institute' clinical guideline on acute and chronic low back pain (2011) listed magnetic resonance neurography as one of the interventions/procedures that are under study and not specifically recommended. Guidelines on ulnar neuropathy from the Washington State Department of Labor and Industries (2010) considered but did not recommend magnetic resonance neurography. Guidelines on radial nerve entrapment from the Washington State Department of Labor and Industries (2010) recommended use of magnetic resonance neurography only in research settings. 

The American College of Radiology’s Appropriateness Criteria® on “Plexopathy” (2012) stated that “Magnetic resonance neurography, diffusion tensor imaging (DTI), and tractography are exciting developments currently under investigation”.

Chung et al (2014) noted that magnetic resonance neurography (MRN) has utility in the diagnosis of many focal peripheral nerve lesions.  The authors stated that when combined with history, examination, electrophysiology, and laboratory data, future advancements in high-field MRN may play an increasingly important role in the evaluation of patients with peripheral neuropathy.

Thawait et al (2014) stated that MRN is a specialized technique that is rapidly becoming part of the diagnostic algorithm of peripheral nerve pathology.  However, in order for this modality to be considered appropriate, its value compared with current methods of diagnosis should be established.  Therefore, radiologists involved in MRN research should use appropriate methodology to evaluate MRN's effectiveness with a multi-disciplinary approach.

The Work Loss Data Institute’s clinical guideline on “Shoulder (acute & chronic)” (2013) listed MRN as one of the interventions/procedures that was considered and not recommended.

Birnbaum et al (2014) stated that the diagnosis and treatment of patients with Sjogren syndrome (SS) with neuropathic pain pose several challenges. Patients with SS may experience unorthodox patterns of burning pain not conforming to a traditional "stocking-and-glove" distribution, which can affect the face, torso, and proximal extremities. This distribution of neuropathic pain may reflect mechanisms targeting the proximal-most element of the peripheral nervous system-the dorsal root ganglia (DRG). Skin biopsy can diagnose such a small-fiber neuropathy and is a surrogate marker of DRG neuronal cell loss. However, SS patients have been reported who have similar patterns of proximal neuropathic pain, despite having normal skin biopsy studies. In such cases, DRGs may be targeted by mechanisms not associated with neuronal cell loss. Thus, alternative approaches are needed to help characterize abnormal DRGs in SS patients with proximal neuropathic pain. These researchers performed a systematic review of the literature to define the frequency and spectrum of SS peripheral neuropathies, and to better understand the attribution of SS neuropathic pain to peripheral neuropathies. They found that the frequency of SS neuropathic pain exceeded the prevalence of peripheral neuropathies, and that painful peripheral neuropathies occurred less frequently than neuropathies not always associated with pain. Thee investigators developed a novel MRN protocol to evaluate DRG abnormalities. A total of 10 SS patients with proximal neuropathic pain were evaluated by this MRN protocol, as well as by punch skin biopsies evaluating for intra-epidermal nerve fiber density (IENFD) of unmyelinated nerves; 5 patients had radiographic evidence of DRG abnormalities. Patients with MRN DRG abnormalities had increased IENFD of unmyelinated nerves compared to patients without MRN DRG abnormalities (30.2 [interquartile range, 4.4] fibers/mm versus 11.0 [4.1] fibers/mm, respectively; p = 0.03). Two of these 5 SS patients whose neuropathic pain resolved with intravenous immunoglobulin (IVIG) therapy had improvement of MRN DRG abnormalities. These researchers developed a novel MRN protocol that can detect DRG abnormalities in SS patients with neuropathic pain who do not have markers of peripheral neuropathy. They found that SS patients with MRN DRG abnormalities had statistically significant, increased IENFD on skin biopsy studies, which may suggest a relationship between trophic mediators and neuropathic pain. The authors concluded that given that this literature review has demonstrated that many SS neuropathic pain patients do not exhibit neuropathies; these findings suggested an important niche for this MRN DRG technique in the evaluation of broader subsets of SS neuropathic pain patients who may not have underlying neuropathies. The improvement of MRN DRG abnormalities in patients with IVIG-induced remission of neuropathic pain suggested that this MRN protocol may be capturing reversible, immune-mediated mechanisms targeting the DRG. The findings of this small case-series study need to be validated by well-designed studies.

Kitazume et al (2014) examined the feasibility of diffusion-weighted MRN (DW-MNR) for determining the originating nerve of para-pharyngeal schwannomas pre-operatively. A total of 6 patients who underwent DW-MRN pre-operatively for a para-pharyngeal schwannoma were studied. Prediction of the originating nerve was performed. With the conventional method, a tumor showing "separation" between the internal jugular vein and carotid artery was determined to originate from the vagus nerve, with "no separation" from the sympathetic chain. With DW-MRN, the relationships between the vagus nerve and sympathetic chain to the tumor were characterized as "connected" or "dislocated". A nerve connected to the tumor was determined as the origin. Surgeries revealed that the origins included 1 vagus nerve and 5 sympathetic chains. Using a conventional method, all 6 cases were diagnosed correctly, whereas DW-MRN successfully predicted only 4 cases with a sympathetic chain origin. The authors concluded that DW-MRN is a feasible approach for determining an originating nerve.

Wang et al (2014) measured relevant anatomical variables of lumbosacral nerve root and adjacent structures by MRN and analyzed operative safety of transforaminal lumbar interbody fusion (TLIF) in Chinese subjects. A total of 12 normal healthy volunteers (6 men and 6 women) underwent MRN of lumbosacral nerve roots at 3.0 T. Three-dimensional imaging was reconstructed with Osirix software and the following anatomic variables measured: (i) distance between nerve root and upper pedicle; (ii) distance between nerve root and lower pedicle; (iii) angle between nerve root and sagittal plane; (iv) distance between upper and lower nerve roots; and (v) distance between upper and lower pedicles. Good images of the L1 to L5 nerve roots were obtained by MRN technology in all 12 volunteers. The distance between nerve root and upper pedicle and the angle between nerve roots and the sagittal plane gradually diminished from L1 to L5. However, there were no significant variations in the distance between nerve root and lower pedicle or between upper and lower pedicles. From L1 to L2 to L4 to L5, the distances between upper and lower pedicles, which are closely related to the operating space for TLIF in Chinese men and women, were less than 10 mm in most subjects and were significantly smaller in women than in men. The variables did not differ significantly between the left and right sides of the same segment. The authors concluded that based on the above anatomical study and measurement analysis, they believed that TLIF puts the upper nerve root at risk in some Chinese patients. Moreover, they stated that this conclusion requires confirmation by anatomical study of large samples and clinical validation.

Yoshida et al (2015) noted that there have been no reports of the use of 3-Tesla MRN (3T MRN) to characterize cervical radiculopathy. In particular, there are no reports of MRN of brachial plexus involvement in patients with cervical radiculopathy. These investigators reviewed retrospectively 12 consecutive patients with cervical radiculopathy who underwent 3T MRN. The median age was 54.5 years; 11 of 12 patients were men. The distribution of nerve-root signal abnormality was correlated with intervertebral foraminal stenosis and the presence of muscles that exhibited weakness and/or signs of denervation on EMG. Abnormalities in MRN were found to extend into the distal part of the brachial plexus in 10 patients. The authors concluded that the findings of this study demonstrated that MRN is potentially useful for diagnosis in patients with suspected cervical radiculopathy. Moreover, they stated that the finding of brachial plexus involvement on MRN may indicate a possible pathophysiological relationship between cervical radiculopathy and brachial plexopathy.

Menezes et al (2015) examined the use of DW-MRN in visualizing the lumbar plexus during pre-operative planning of lateral transpsoas surgery. A total of 94 (188 lumbar plexuses) spine patients underwent a DW-MR examination of the lumbar plexus in relation to the L3 to L4 and L4 to L5 disc spaces and superior third of the L5 vertebral body. Images were reconstructed in the axial plane using high-resolution Maximum Intensity projection (MIP) overlay templates at the disc space and L3 to L4 and L4 to L5 interspaces; 10 and 22 mm MIP templates were chosen to mimic the working zone of standard lateral access retractors. The positions of the L4 nerve root and femoral nerve were analyzed relative to the L4 to L5 disc in axial and sagittal planes. Third-party radiologists and a senior spine surgeon performed the evaluations, with inter- and intra-observer testing performed. In all subjects, the plexus was successfully mapped. At L3 to L4, in all but 1 case, the components of the plexus (except the genito-femoral nerve) were located in the most posterior quadrant (zone IV). The L3 and L4 roots coalesced into the femoral nerve below the L4 to L5 disc space in all subjects. Side-to-side variation was noted, with the plexus occurring in zone IV in 86.2 % right and only 78.7 % of left sides. At the superior third of L5, the plexus was found in zone III in 27.7 % of right and 36.2 % of left sides; and in zone II in 4.3 % right and 2.1 % left sides. Significant inter- and intra-observer agreement was found. The authors concluded that by providing the surgeon with a pre-operative roadmap of the lumbar plexus, DW-MRN may improve the safety profile of lateral access procedures. These findings need to be validated by well-designed studies.

In an observational study, Quinn and colleagues (2015) demonstrated use of MRN to visualize the course of the lumbar plexus at the L4 to L5 disc space. Consecutive lumbar plexus MR neurograms (n = 35 patients, 70 sides) were studied. Scans were obtained on a Siemens 3T Skyra magnetic resonance imaging scanner. T1- and T2-color-coded fusion maps were generated along with 3-D models of the lumbosacral plexus with attention to the L4 to L5 interspace. The position of the plexus and the shape of the psoas muscle at the L4 to L5 interspace were evaluated and recorded. Direct imaging of the lumbar plexus using MRN revealed a substantial variability in the position of the lumbar plexus relative to the L4 to L5 disc space. The left-side plexus was identified in zone 2 (5.7 %), zone 3 (54.3 %), and zone 4 (40 %) (p = 0.0014); on the right, zone 2 (8.6 %), zone 3 (42.9 %) or zone 4 (45.7 %), and zone 5 (2.9 %) (p = 0.01). Right-left symmetry was found in 18 of 35 subjects (51.4 %) (p = 0.865). There was no association between the position of the plexus and the shape of the overlying psoas muscle identified. In patients with an elevated psoas (n = 12), the lumbar plexus was identified in zone 3 in 75 % and 66 % (left and right) compared with patients without psoas elevation (n = 23), 30.4 % and 43.5 % (left and right). The authors concluded that the course of the lumbosacral plexus traversing the L4 to L5 disc space may be more variable than has been suggested by previous studies. They stated that MRN may provide a more reliable means of pre-operatively identifying the plexus when compared with current methods. These findings need to be validated by well-designed studies.

Currently, the sensitivity, specificity, as well as PPV and NPV of MR neurography in the diagnosis and management of patients with peripheral nerve disorders remain unclear.  Thus, the accuracy and clinical value of MR neurography has yet to be established.

CPT Codes / HCPCS Codes / ICD-9 Codes
There are no specific codes for magnetic resonance neurography:
ICD-9 codes not covered for indications listed in the CPB (not all inclusive) :
350.1 - 359.9 Disorders of the peripheral nervous system
950.0 - 957.9 Injury to nerves and spinal cord
CPT Codes / HCPCS Codes / ICD-10 Codes
Information in the [brackets] below has been added for clarification purposes.   Codes requiring a 7th character are represented by "+":
ICD-10 codes will become effective as of October 1, 2015 :
There are no specific codes for magnetic resonance neurography:
ICD-10 codes not covered for indications listed in the CPB (not all-inclusive) :
G50.0 - G59 Nerve, nerve root and plexus disorders
S04.011+ - S04.9xx+
S14.0xx+ - S14.9xx+
S24.0xx+ - S24.9xx+
S34.01x+ - S34.9xx+
S44.00x+ - S44.92x+
S54.00x+ - S54.92x+
S64.00x+ - S64.92x+
S74.00x+ - S74.92x+
S84.00x+ - S84.92x+
S94.00x+ - S94.92x+
Injury to nerves and spinal cord


The above policy is based on the following references:
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