Imaging of the Peripheral Nerves

As a complement to clinical history, physical examination, and electrodiagnostic studies, the use of ultrasound (US) and magnetic resonance (MR) imaging is an essential part of the diagnostic work-up in patients with peripheral neuropathies. Electrophysiology, the clinical gold standard for nerve assessment, does not always provide a conclusive diagnosis, especially when the disease presentation is atypical. In addition, functional studies have limitations in assessing the exact location, cause, and extent of a nerve lesion and the concurrent disease of surrounding tissues. In these instances, imaging can play an important role in offering a precise morphological correlate of functional data, thus allowing clinicians to complete the diagnostic assessment and make patient management more effective in a variety of pathological conditions such as entrapment syndromes, traumatic injuries, and space-occupying lesions.

MR imaging currently offers excellent visualization of nerve anatomy and the depiction of a wide spectrum of pathological conditions. As technology progresses, a variety of new imaging techniques such as MR neurography, diffusion tensor imaging, and fiber tractography will make MR imaging of nerves increasingly detailed and more useful. In contrast, despite the inherent operator dependency and a longer learning curve, US provides speed of performance and important advantages over MR imaging, including a higher spatial resolution that makes it possible to demonstrate very small distal branches (even <1 mm thick), the ability to explore long nerve segments in a single sweep, and last, but not least, its dynamic capabilities with real-time scanning during joint motion or muscle contraction. Neurologists are finding that combining electrodiagnosis and US regardless of the patient's disorder is redefining the way the nerve diseases are conceptualized and managed. In the last decade, US and MR imaging have become competitive for imaging nerves. Until now, however, too few blinded research studies were available to compare the effectiveness of either imaging modality and to offer guidelines on which one should be used first. The selection of the most adequate imaging technique depends on factors such as access, expertise, costs, clinician preference, the anatomical area to be imaged, and the suspected pathology. Thus some articles in this issue are US based and others are essentially oriented toward MR imaging.

I was honored to edit this issue of Seminars in Musculoskeletal Radiology, and I would like to thank the editors for offering me the opportunity. This issue contains a collection of excellent articles focused on various aspects of peripheral nerve imaging written by a panel of internationally renowned experts in the field. I am most grateful to all of the authors who contributed the outstanding articles in this issue. The journal includes an introductory article on technological advances written by Kermarrec and colleagues from Lille, France. The three articles that follow review US and MR imaging in entrapment neuropathies. Jacobson and colleagues from Ann Arbor, Michigan, discuss the entrapment syndromes in the upper limb; Klauser and colleagues from Innsbruck, Austria, the carpal tunnel syndrome; and Beltran and colleagues from New York City the entrapment syndromes of the lower limb. Our group then discusses the value of imaging in assessing traumatic injuries, and the always challenging topic of brachial plexus and other nerves about the shoulder girdle. Woertler from Munich, Germany, reviews tumors and tumor-like lesions of nerves. Lastly, Tagliafico and colleagues illustrate interventional ultrasound procedures in this field. I hope readers will find the information in this issue both useful and educational.