Editorial
Copyright ©The Author(s) 2016. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Radiol. Aug 28, 2016; 8(8): 726-728
Published online Aug 28, 2016. doi: 10.4329/wjr.v8.i8.726
Peripheral nerve imaging: Not only cross-sectional area
Alberto Stefano Tagliafico
Alberto Stefano Tagliafico, Department of Experimental Medicine, DIMES, Institute of Anatomy, University of Genova, 16132 Genova, Italy
Author contributions: Tagliafico AS solely contributed to the paper.
Conflict-of-interest statement: The author declares no conflicts of interest regarding this manuscript.
Open-Access: This article is an open-access article which was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/4.0/
Correspondence to: Alberto Stefano Tagliafico, MD, Radiologist, Assistant Professor of Human Anatomy, Department of Experimental Medicine, DIMES, Institute of Anatomy, University of Genova, Via de Toni 14, 16132 Genova, Italy. alberto.tagliafico@unige.it
Telephone: +39-010-3537882 Fax: +39-010-3537885
Received: March 17, 2016
Peer-review started: March 19, 2016
First decision: April 15, 2016
Revised: April 19, 2016
Accepted: June 14, 2016
Article in press: June 16, 2016
Published online: August 28, 2016

Abstract

Peripheral nerve imaging is recognized as a complement to clinical and neurophysiological assessment in the evaluation of peripheral nerves with the ability to impact patient management, even for small and difficult nerves. The European Society of Musculoskeletal Radiology, suggest to use ultrasound (US) for nerve evaluation due to the fact that, in sever anatomical area, magnetic resonance imaging is not able to give additional informations. US could be considered the first-choice approach for the assessment of peripheral nerves. The relative drawback of peripheral nerve US is the long learning curve and the deep anatomic competence to evaluate even small nerves. In the recent years, the role of US in peripheral nerve evaluation has been widened. In the past, nerve US was mainly used to assess nerve-cross sectional area, but now more advanced measurements and considerations are desirable and can boost the role of peripheral nerve US. Nerve echotexture evaluation was defined in 2010: The ratio between the hypoechoic and hyperechoic areas of peripheral nerves on US was called “nerve density”. For evaluation of patients who have peripheral neuropathies, the role of peripheral nerve is US wider than simple cross-sectional area evaluation. Quantitative measurements describing the internal fascicular echotexture of peripheral nerves introduce the concept of considering US as a possible quantitative imaging biomarker technique. The potential of nerve US has started to be uncovered. It seems clear that only cross-sectional area measurement is no more sufficient for a comprehensive US evaluation of peripheral nerves.

Key Words: Ultrasound, Imaging, Magnetic resonance imaging, Nerve density, Fascicular ratio

Core tip: Ultrasound (US) is a possible quantitative imaging biomarker technique for peripheral nerves evaluation. The potential of nerve US has therefore started to be uncovered and it seems clear that only cross-sectional area measurement is no more sufficient for a comprehensive US evaluation of peripheral nerves.



INTRODUCTION

Peripheral nerve imaging is recognized as a complement to clinical and neurophysiological assessment in the evaluation of peripheral nerves with the ability to impact patient management, even for small and difficult nerves[1-7]. In daily radiological clinical practice, ultrasound (US) and magnetic resonance imaging (MRI) are the technics of choice. The European Society of Musculoskeletal Radiology, suggest to use US for nerve evaluation due to the fact that, in sever anatomical area, MRI is not able to give additional informations[8]. For deep nerve or central disease, conventional MRI, MRI neurography, diffusion tensor imaging, fiber tractography[9] and 3D MRI[10] are promising but are not always available and need long acquisition time. Therefore, US could be considered the first-choice approach for the assessment of peripheral nerves. US is a relative low-cost technique, widely available and with dynamic capabilities[1-13]. In addition, evaluation of the entire limb during a unique exam is possibly with great spare of time compared to MRI. The relative drawback of peripheral nerve US is the long learning curve and the deep anatomic competence to evaluate even small nerves[1-14]. To improve the knowledge of peripheral nerve US, the International Society of Peripheral Neurophysiological Imaging (http://www.ispni.org/), founded in 2014, supports the pivotal role of peripheral nerve US in the assessment of patients with suspect peripheral nerve pathological involvement. Not surprisingly, in the recent years, the role of US in peripheral nerve evaluation has been widened[15,16]. In the past, nerve US was mainly used to assess nerve-cross sectional area[17-22], but now more advanced measurements and considerations are desirable and can boost the role of peripheral nerve US.

Nerve echotexture evaluation was defined in 2010. Our research group, using US, developed a software that quantifies the ratio between the hypoechoic and hyperechoic areas of peripheral nerves on US[23]. We called this parameter: “nerve density”[23]. We evaluated sixty-five different patients and (n = 65) controls (age range, 35-81 years; mean 55 years) prospectively. Nerve density was capable of discriminating between normal and pathologic nerves of patients affected by carpal tunnel syndrome or neurofibromas. Moreover, nerve density measure was useful to discriminate between patients with mild and severe Carpal Tunnel Syndrome[23].

In addition, we defined and quantitatively evaluated the fascicular ratio (FR) on MRI in patients with peripheral neuropathies compared with healthy controls[24,25]. On MRI, FRs were significantly increased in patients compared with controls (FR, 76.7 ± 15.1 vs 56 ± 12.3; P < 0.0001 for the semiautomatic interface; and FR 66.3 ± 17.5 vs 47.8 ± 18.4; P < 0.0001 for the automatic interface). The increase in FR was caused mainly by an increase in the hypointense part of the nerve and this observation was valid for all causes of neuropathies[24,25].

CONCLUSION

For evaluation of patients who have peripheral neuropathies, the role of peripheral nerve is US wider than simple cross-sectional area evaluation[25]. Quantitative measurements describing the internal fascicular echotexture of peripheral nerves introduce the concept of considering US as a possible quantitative imaging biomarker technique[22]. Indeed, quantitative assessment of nerve echogenicity or the FR has been considered a step further in the evaluation of peripheral nerves by the means of US[23-27]. The potential of nerve US has started to be uncovered. It seems clear that only cross-sectional area measurement is no more sufficient for a comprehensive US evaluation of peripheral nerves.

Footnotes

Manuscript source: Invited manuscript

Specialty type: Radiology, nuclear medicine and medical imaging

Country of origin: Italy

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P- Reviewer: Chow J, Gao BL, Nouh MR S- Editor: Qiu S L- Editor: A E- Editor: Zhang FF

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