Functional MR Neurography in Evaluation of Peripheral Nerve Trauma and Postsurgical Assessment (original) (raw)
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Journal of plastic, reconstructive & aesthetic surgery : JPRAS, 2020
Diagnosing the site and severity of peripheral nerve injuries can be challenging for clinicians. The current gold standards of evaluation with clinical examination and electrophysiology have respective limitations, particularly with determining the prognosis for spontaneous recovery. Current imaging techniques with ultrasound, computed tomography, and magnetic resonance imaging (MRI) may be used as adjuncts in the evaluation of peripheral nerve injuries but are limited in sensitivity and accuracy. Diffusion tensor imaging (DTI) is a recent advancement in MRI sequences that shows promise in evaluating peripheral nerve injuries. Unlike the qualitative traditional MRI, DTI captures the pattern of water diffusion along the nerves and provides quantitative information regarding the integrity of axons. Additionally, DTI images can be reconstructed into 3D images with tractography. This technique is well-established in the central nervous system but is only starting to be applied in the pe...
Quantitative Imaging in Medicine and Surgery
Traumatic conditions of peripheral nerves and plexus have been classically evaluated by morphological imaging techniques and electrophysiological tests. New magnetic resonance imaging (MRI) studies based on 3D fat-suppressed techniques are providing high accuracy for peripheral nerve injury evaluation from a qualitative point of view. However, these techniques do not provide quantitative information. Diffusion weighted imaging (DWI) and diffusion tensor imaging (DTI) are functional MRI techniques that are able to evaluate and quantify the movement of water molecules within different biological structures. These techniques have been successfully applied in other anatomical areas, especially in the assessment of central nervous system, and now are being imported, with promising results for peripheral nerve and plexus evaluation. DWI and DTI allow performing a qualitative and quantitative peripheral nerve analysis, providing valuable pathophysiological information about functional integrity of these structures. In the field of trauma and peripheral nerve or plexus injury, several derived parameters from DWI and DTI studies such as apparent diffusion coefficient (ADC) or fractional anisotropy (FA) among others, can be used as potential biomarkers of neural damage providing information about fiber organization, axonal flow or myelin integrity. A proper knowledge of physical basis of these techniques and their limitations is important for an optimal interpretation of the imaging findings and derived data. In this paper, a comprehensive review of the potential applications of DWI and DTI neurographic studies is performed with a focus on traumatic conditions, including main nerve entrapment syndromes in both peripheral nerves and brachial or lumbar plexus.
Plastic and Aesthetic Research, 2015
Peripheral nerve injuries are a heterogeneous group of lesions that may occurs secondary to various causes. Several different classifications have been used to describe the pathophysiological mechanisms leading to the clinical deficit, from simple and reversible compression-induced demyelination, to complete transection of nerve axons. Neurophysiological data localize, quantify, and qualify (demyelination vs. axonal loss) the clinical and subclinical deficits. High-resolution ultrasound can demonstrate the morphological extent of nerve damage, fascicular echotexture (epineurium vs. perineurium, focal alteration of the cross-section of the nerve, any neuromas, etc.), and the surrounding tissues. High field magnetic resonance imaging provides high contrast neurography by fat suppression sequences and shows structural connectivity through the use of diffusion-weighted sequences. The aim of this review is to provide clinical guidelines for the diagnosis of nerve injuries, and the rationale for instrumental evaluation in the preoperative and postoperative periods. While history and clinical approach guide neurophysiological examination, nerve conduction and electromyography studies provide functional information on conduction slowing and denervation to assist in monitoring the onset of re-innervation. High-resolution nerve imaging complements neurophysiological data and allows direct visualization of the nerve injury while providing insight into its cause and facilitating surgical treatment planning. Indications and limits of each instrumental examination are discussed.
Diffusion tensor imaging to visualize axons in the setting of nerve injury and recovery
Neurosurgical focus, 2015
Successful management of peripheral nerve trauma relies on accurate localization of the injury and grading of the severity of nerve injury to determine whether surgical intervention is required. Existing techniques, such as electrodiagnostic studies and conventional imaging modalities, provide important information, but are limited by being unable to distinguish severe nerve lesions in continuity that will recover from those that will not. Diffusion tensor imaging (DTI) and tractography of peripheral nerves provide a novel technique to localize and grade nerve injury, by assessing the integrity of the nerve fibers across the site of nerve injury. Diffusion tensor imaging and tractography also hold promise as markers of early nerve regeneration, prior to clinical and electrodiagnostic evidence of recovery. In the present review, the techniques of peripheral nerve DTI and tractography are discussed with respect to peripheral nerve trauma, with illustrative cases demonstrating potentia...
Journal of …, 1996
ISSUE-selective images of bone and blood vessels play prominent roles in clinical diagnosis. Direct images of nerves, however, have not been available in the past. The advent of magnetic resonance (MR) neurography 14,26 now makes it possible to learn how such images can alter and improve the process of neurological diagnosis. Radiological images of structures adjacent to nerves are used extensively in diagnosis; 3,56 however, data concerning the nerves themselves arise primarily from the patient's clinical history, neurological examination, and electrodiagnostic tests. 30,36 The x-ray-absorptive properties of nerves provide little distinction from surrounding tissues; 19,46 conventional MR imaging of nerves has been restricted to a limited number of sites in the body, 8,29 and their ultrasound imaging 21 is even more limited. Recently, there have been reports of MR imaging protocols that achieve dramatic increases in the conspicuity of nerve. 26,27 The result is a novel type of medical image termed an "MR neurogram." The "diffusion-based" methods of this technique first reported have very high nerve selectivity, but require strong magnetic field gradients 12 not generally available for clinical MR imaging.
MR neurography: diagnostic utility in the surgical treatment of peripheral nerve disorders
Neuroimaging clinics of North America, 2004
Advances in MR imaging have improved the visualization of normal and pathologic peripheral nerve structures in various clinical settings. Peripheral nerve imaging has the potential to dramatically change the diagnosis and treatment of peripheral nerve pathology and lead to an improved understanding of peripheral nerve pathophysiology. Currently, MR imaging serves as a problem-solving tool when additional anatomic information is needed to clarify ambiguous electrodiagnostic and clinical examinations. The next major advance in MR imaging of peripheral nerves will likely be the transition from anatomic to physiologic imaging with higher resolution as better phased-array surface coils and higher-field-strength magnets become available. Finally, MR neurography should remain complementary to the clinical examination and electrodiagnostic studies in the evaluation of peripheral nerve disorders.
Peripheral Nerve Surgery: The Role of High-Resolution MR Neurography
American Journal of Neuroradiology, 2011
High-resolution MRN is becoming increasingly available due to recent technical advancements, including higher magnetic field strengths (eg, 3T), 3D image acquisition, evolution of novel fat-suppression methods, and improved coil design. This review describes the MRN techniques for obtaining high-quality images of the peripheral nerves and their small branches and imaging findings in normal as well as injured nerves with relevant intraoperative correlations. Various microsurgical techniques in peripheral nerves, such as neurolysis, nerve repairs by using nerve grafts, and conduits are discussed, and MRN findings of surgically treated nerves are demonstrated.
Diffusion tensor imaging and tractography of distal peripheral nerves at 3 T
Clinical Neurophysiology, 2005
Objective: We studied whether distal peripheral nerves could be imaged using quantitative diffusion tensor imaging (DTI) with a 3-T MRI scanner, and visualized using tractography. Methods: Altogether 6 healthy subjects were studied. The diffusion was quantified with apparent diffusion coefficient (ADC) and fractional anisotropy (FA) maps, and the direction of main diffusivity was visualized with color-coded orientation maps and tractography. Results: We present the first DTI and tractography results of human distal peripheral nerves. The courses of median, ulnar, and radial nerves in the upper limb and of tibial and peroneal nerves in the lower limb were first analyzed quantifying ADC and FA, and then visualized in 3D with tractography. Tractography illustrated nicely the 3D courses of both upper and lower limb nerves which were reliably distinguished from the surrounding muscle tissue and ligaments. Conclusions: Quantitative DTI and tractography can be used to image and visualize distal peripheral nerves. Significance: DTI is a quantitative method that could provide useful information for the diagnosis and follow-up of nerve lesions, entrapments, and regeneration. Peripheral nerves as well-delineated structures also containing abundant branching into bundles of different diameters, could be used as 'living phantoms' for testing and validating different tractography methods.
Experimental Neurology, 2004
Acute axonal nerve lesions cause a hyperintense signal on T2-weighted (T2-w) magnetic resonance imaging (MRI) at the nerve lesion site and distal to it. The aim of this experimental study was to investigate the spatiotemporal evolution and resolution of MR nerve signal changes following denervation and reinnervation, and to relate these findings to electrophysiology and histology. The proximal sciatic nerve of adult rats was ligated by a tight suture that was removed 1 week later to induce complete axotomy and nerve regeneration upon release. Serial electromyography (EMG) and motor nerve conduction studies were performed parallel to MRI at multiple points of time. Moreover, sciatic nerves were taken for quantitative histological evaluation. Nerve hyperintensity on T2-w MRI was present distal to the lesion at thigh level 24 h after denervation preceding the occurrence of spontaneous activity on EMG by 24 h. After 48 h, the entire sciatic nerve and its branches showed an increased signal down to the level of the lower leg. The increased nerve signal regressed with a proximo-distal gradient beginning from week 2 after onset of nerve regeneration in the thigh. On EMG, the first reinnervation potentials were detected at that time at the respective level. Compound muscle action potential (CMAP) in the foot muscle fully recovered 12 weeks after onset of nerve regeneration, that is, 2 weeks after resolution of the hyperintensity along the entire nerve on MRI. Histology revealed axonal degeneration in the acute phase and later nerve oedema parallel to the increased nerve signal on MRI. MR signal alterations occur as early as 24 h after an axonal nerve lesion and correlate with nerve fiber degeneration and later with nerve oedema on histology. MR findings in denervation and reinnervation parallel the electrophysiological changes. Thus, MRI is a promising diagnostic tool for the early detection of acute axonal nerve lesions and monitoring of nerve regeneration.