NEW PARADIGMS FOR ULTRASOUND: ASSESSING PERIPHERAL NERVES
CONTINUED FROM PART I
Our last blog discussed the gradual ascendancy of ultrasound /sonographic evaluation(s) within the field of musculoskeletal anatomy, and more specifically in assessing pathologies for peripheral nerves. This material was presented earlier this year at the 2019 American Institute of Ultrasound in Medicine (AIUM) Annual Convention.
We covered the rapid technological improvements over the past 4-5 years, and briefly outlined how this offers many advantages to both the patient and the examining medical professional. Aside from the inherent cost-advantages previously discussed, creating a less imposing or obtrusive examination environment fulfills the fundamental goal of improving patient care by facilitating communication and feedback in addition to reducing stress/anxiety.
BEST PRACTICES PRE-EXAM –
It is important to ascertain if the patient has undergone any surgical procedures that may have altered the normal anatomy. The examiner should be familiar with the normal post-surgical sonographic characteristics of affected tissue so that it is not mistaken for pathology.
While obtaining a detailed patient history, try to determine the mechanism of injury in order to concentrate on the most likely structure(s) creating pain. Additionally, encourage the patient to discuss any accident, sports-related or overuse injury, acute trauma, or chronic microtrauma which may point you toward a specific muscle/nerve group.
If none of the above conditions is identified, it is critical to understand the types of symptoms the patient is experiencing. For example, exercise-related pain can be caused by a degenerative joint disease or tendinopathy. Night pain could be related to an inflammatory condition. Burning, tingling or numbness could be suggestive of nerve entrapment.
Having identified the likely-affected muscle or nerve group, inspect and palpate the proximate skin and subcutaneous tissue for bruising or ecchymosis, tenderness, inflammation or dysfunction. Ascertain what kind of movement produces pain and evaluate a full range of movements, attempting to reproduce the conditions associating with the patient’s discomfort.
In summary, a detailed history and physical exam are critical to determining what areas and structures to scan.
TRANSDUCER SELECTION –
Depending on the area of interest, you should select either a linear or curved linear transducer. As referenced previously, higher frequency transducers are appropriate to provide the precise detail resolution specific to nerve studies. This superior spatial resolution comes at the expense of penetration, unfortunately. Therefore, in evaluating deeper structures (e.g. abdomen or hip) a lower-frequency transducer may be required.
In addition to the “standard” linear transducer with a larger footprint, a smaller-faced version exists, often referred to as a “hockey stick” because of its shape. This type of probe is optimal for imaging the hand, ankle, and foot because it provides better contact around the curves of the bones in these areas. Recalling that air is the proverbial gremlin of ultrasound studies, a generous amount of transmission gel should be used to improve the imaging of these extremities.
In evaluations of nerve/muscle structures with bilateral counterparts, ultrasound images should be captured from each “side” for comparative purposes, especially when subtle pathology is suspected. This is another inherent advantage of MSK ultrasound exams insomuch as it doesn’t require a complicated, separate imaging procedure.
Dynamic evaluation is another superior feature of MSK ultrasound studies, comparing favorably against older technologies. This dynamic/real-time imaging of the nerves and muscles in motion helps differentiate them from the surrounding structures for better visualization. A familiarity with localized anatomy is fundamental. For example, when scanning a nerve in the short axis from proximal to distal in motion, a muscle will eventually become a tendon which attaches to bone, whereas a nerve will continue until it divides. Observing the nerves in motion also allows the sonographer to recognize a normal “honeycomb” appearance of a nerve, distinguishing it from surrounding soft tissue.
In the next blog, I will have some final thoughts and insights on evaluating the ultrasound image and optimizing settings.
Jamie Bie is the Senior Musculoskeletal Ultrasound Specialist at Columbia University/New York Presbyterian Imaging. She was awarded the ARDMS Pioneer Musculoskeletal Ultrasound credential in 2012. In addition to holding the RMSKS credential, she is also registered in Vascular Technology, Abdomen, OB/GYN, and Breast. Jamie has written departmental protocols and has trained several physicians and sonographers in Musculoskeletal Ultrasound.
Jamie Bie is also the author of newly-released Musculoskeletal Ultrasound: A Comprehensive Guide to MSK Imaging and Interventional Techniques, a comprehensive, step-by-step guide to MSK Ultrasound. This textbook includes an overview of MSK Ultrasound physics, illustrated protocols, anatomy review by section, transducer and ultrasound overlays to clarify positioning and structure recognition, and CheckPoints noted throughout the text, providing critical technical tips.