New approaches in imaging of the brachial plexus

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Abstract

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 2D MR sequences to study the brachial plexus: the 3D STIR SPACE sequence, 3D heavily T2w MR myelography sequences (balanced SSFP = CISS 3D, True FISP 3D, bFFE and FIESTA), and the diffusion-weighted (DW) neurography sequence with fiber tracking reconstruction (tractography). The 3D 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 postganglionic nerve fibers thanks to the capability of performing maximum intensity projections (MIP) and multiplanar 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 postganglionic 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.

Introduction

The brachial plexus provides motor and sensory innervation to the upper extremity. Pathologic conditions involving the brachial plexus are uncommon. They are frequently misdiagnosed with unfortunate disastrous consequences. As clinical assessment of the brachial plexus constitutes a real challenge and electrophysiological studies may inadequately identify and characterize the cause and location of brachial plexus impairment, MR imaging has become the evaluation method of choice because of its multiplanar capabilities and excellent soft tissue contrast. Consequently, electromyography and MRI are used as complementary tools to assess brachial plexopathy and the correlation of MR findings with electrophysiologic results increases specificity and sensitivity, as suggested by some investigators [1].

Brachial plexopathy develops when lesions occur anywhere along the course of the brachial plexus. Causes of brachial plexopathy include primary and secondary tumors, trauma, entrapment and irradiation. The current role of MR imaging in brachial plexopathy consists in distinguishing between preganglionic and postganglionic injury, localizing precisely a lesion, characterizing it and answering the important questions whether we are dealing with stretching, rupture or nerve avulsion in cases of traumatic injury. It also consists in assessing whether the fibers are displaced, compressed or infiltrated by a tumor or an inflammatory process and whether there is entrapment and compression by congenital bands, hypertrophied scalene muscles or rudimentary cervical ribs. Despite recent improvements in MR technology, analysis of the brachial plexus and answers to these clinically relevant questions remain difficult with conventional 2D MR techniques due to the angulated spatial orientation, topographic location, morphology and size of the roots, trunks, divisions, cords and terminal branches of the brachial plexus [2]. Major disadvantages of these conventional 2D imaging techniques include their inability to obtain 3D maximum intensity projection (MIP) images that better depict the entire length of nerve sheaths and the difficulty to differentiate venous structures from adjacent nerve fibers, as both structures often have a similar signal intensity on T1 and T2w images. The addition of recently developed 3D imaging techniques and diffusion-weighted sequences to the conventional 2D MR imaging protocol helps to overcome the difficulties in precise lesion localization and image interpretation.

The purpose of this article is to review the role of current standard MR protocols used in the evaluation of the brachial plexus, to familiarize the reader with recently developed 3D imaging techniques, diffusion-weighted imaging and tractography techniques and to illustrate and discuss their potential implications in disease management and treatment planning. To better understand the importance of imaging brachial plexus lesions, we will start our discussion with a brief review of the pertinent anatomy.

Section snippets

Normal anatomy

The brachial plexus is a network of nerves formed by the ventral branches of the spinal nerves C5–T1 in the posterior neck triangle and with variable minor contributions from C4 or T2. The roots of the brachial plexus combine to form three trunks: upper, middle and lower trunk (Fig. 1, Fig. 2). The three trunks course between the anterior and middle scalene muscles in proximity of the subclavian artery and lie in the scalene triangle. The upper trunk is formed by the roots of C5 and C6, the

MR techniques and imaging protocols

Although 3 T MR imaging is being increasingly performed for clinical purposes because of its potential to improve spatial and temporal resolution, most investigators including ourselves prefer MR imaging of the brachial plexus at 1.5 T because of reduced B0 and B1 inhomogeneity and minimized susceptibility artifacts. In our hospital, we are currently using a 1.5 T Avanto scanner (Siemens Medical Systems, Erlangen, Germany) to image brachial plexopathy. Patients are scanned in the supine position

Tumor mass involving the brachial plexus

In tumoral pathology, MR imaging is used to assess whether a mass is intrinsic or extrinsic to the brachial plexus and to precisely determine the site of the displaced, compressed or destroyed nerve fibers. The information from MR imaging is also used in the pre-operative planning procedure.

The most common malignant tumors involving the brachial plexus are extrinsic lesions and include: direct extension from non-neurogenic malignant tumors (typically lung cancer), lymphoma and metastases (most

Conclusion

The newly developed 3D STIR SPACE sequence offers high resolution MR imaging of postganglionic brachial plexus lesions. It is a valuable tool for the diagnosis of a variety of neoplastic, traumatic, congenital and post-treatment plexus lesions, as well as for planning of surgical interventions. The 3D heavily T2w MR myelography sequences are mandatory in the evaluation of preganglionic traumatic lesions. DW neurography with tractography of the brachial plexus are new techniques that require

References (23)

  • M.I. Vargas et al.

    Clinical findings, electroneuromyography and MRI in trauma of the brachial plexus

    J Neuroradiol

    (2007)
  • M.C. Petit-Lacour et al.

    MRI of the brachial plexus

    J Neuroradiol

    (2004)
  • P. Hagmann et al.

    DTI mapping of human brain connectivity: statistical fibre tracking and virtual dissection

    Neuroimage

    (2003)
  • R.A. Nardin et al.

    Electromyography and MRI in the evaluation of radiculopathy

    Muscle Nerve

    (1999)
  • K.E. Chappell et al.

    Magic angle effects in MR neurography

    AJNR Am J Neuroradiol

    (2004)
  • H.W. Van Es

    MRI of the brachial plexus

    Eur Radiol

    (2001)
  • M. Viallon et al.

    High-resolution and functional magnetic resonance imaging of the brachial plexus using an isotropic 3D T2 STIR (short term inversion recovery) SPACE sequence and diffusion tensor imaging

    Eur Radiol

    (2008)
  • X. Buy et al.

    Imagerie des avulsions du plexus cervico-brachial: intérêt de la séquence IRM CISS 3D

    Feuill Radiol

    (2001)
  • R. Gasparotti et al.

    Three-dimensional MR myelography of traumatic injuries of the brachial plexus

    AJNR Am J Neuroradiol

    (1997)
  • T. Yoshikava et al.

    Brachial plexus injury: clinical manifestations, conventional imaging findings and the latest imaging techniques

    Radiographics

    (2006)
  • N. Ramli et al.

    High resolution CISS imaging of the spine

    Br J Radiol

    (2001)
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