Ultrasound Evaluation of Focal Neuropathies · 2013-12-13 · Ultrasound Evaluation of Focal Neuropathies New York Correlation With Electrodiagnosis Jeffrey A. Strakowski, MD Clinical

Ultrasound Evaluation of Focal Neuropathies

DVD INCLU

DEDJ e f f r e y A . S t r A k o w S k i

Correlation with Electrodiagnosis


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New York

Correlation With Electrodiagnosis

Jeffrey A. Strakowski, MDClinical Associate Professor of Medicine

Department of Physical Medicine and RehabilitationThe Ohio State University

Associate Director of Medical EducationDepartment of Physical Medicine and Rehabilitation

Riverside Methodist Hospital

Director of Musculoskeletal ResearchThe McConnell Spine, Sport & Joint Center

Columbus, Ohio

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ISBN: 978-1-936287-67-3e-book ISBN: 978-1-61705-115-9

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Library of Congress Cataloging-in-Publication DataStrakowski, Jeffrey A. Ultrasound evaluation of focal neuropathies : correlation with electrodiagnosis / Jeffrey A. Strakowski. p. ; cm. Includes bibliographical references and index. ISBN 978-1-936287-67-3—ISBN 978-1-61705-115-9 (e-book)

I. Title. [DNLM: 1. Nerve Compression Syndromes—ultrasonography. 2. Electrodiagnosis. 3. Nerve Compression Syndromes—diagnosis. WL 520] RC366 616.85’607547—dc23

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v

Foreword Ernest W. Johnson, MD vii

Preface ix

Acknowledgements xi

1. Introduction 1

2. Electrodiagnostic Assessment of Peripheral Neuropathies 11

3. Introduction to High-Frequency Ultrasound 27

4. Ultrasound Evaluation of Peripheral Nerves 65

5. Evaluation of the Brachial Plexus and Thoracic Outlet 95

6. Evaluation of Nerves About the Neck and Shoulder 127

7. Evaluation of the Radial Nerve 159

8. Evaluation of the Median Nerve 195

9. Evaluation of the Ulnar Nerve 269

10. Evaluation of Nerves About the Hip and Thigh 313

11. Evaluation of the Fibular Nerve 349

12. Evaluation of the Tibial Nerve 375

13. Evaluation of Other Sensory Nerves Around the Leg, Foot, and Ankle 393

14. Ultrasound in Generalized Neuromuscular Conditions 415

15. Future Directions for Ultrasound of Peripheral Nerve and Focal Neuropathies 433

Video Captions 441

Index 451

Contents

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With technology advancing, it was inevitable that these frequently occurring focal neuropathies would be targets for advancing electrodiagnosis for functional loss and imaging for the accompany-ing structural abnormalities. In these circumstances, high-frequency ultrasound is proving to be the opti-mal imaging modality. The information gained from the combination of these diagnostic tools with respect to both functional and structural changes can result in more successful management.

Diagnostic limitations occur when only a single facet of a clinical problem is evaluated. Assessing only function or structure in isolation can lead to incomplete understanding and suboptimal manage-ment. This combination of diagnostic technologies, with an expert clinician who is completely conver-sant with precise anatomy, assures greater accuracy in identifying problems and better outcomes for indi-vidual patients.

This book presents specifi c techniques for the application of ultrasound to study the anatomic relationships of structures at nerve entrapment sites (vulnerabilities) in the region of the neck and in the upper and lower limbs. The diagnosis of these vul-nerable nerve sites in the body rests on the specifi c loci of loss of function. Electrodiagnosis can local-ize the functional loss and provide an objective data

set. However, to completely evaluate an insult to the nerve, structural images are necessary.

Although MRI is available, it often has less reso-lution and does not provide information on vascular fl ow or dynamic abnormalities that are often needed for full understanding. Ultrasound does all this and is typically more practical for routine screening of abnormalities, both from a cost containment stand-point and for relative convenience for the patient.

To use ultrasound effectively to identify pre-cisely the cause, degree of the loss of function, and structural abnormalities at the site of insult requires special knowledge and training. The following are necessary qualifi cations:

expert clinical skills• specifi c and thorough knowledge of anatomy• expertise in electrodiagnosis• thorough and practical ability in musculoskeletal • and neuromuscular ultrasoundexperience to put it all together•

Is there a single author who could put this information in a book to help others learn and apply these techniques? An expert clinician with thor-ough understanding of problems of neuromuscular entrapments, electrodiagnosis, and advanced skills

Foreword

vii

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viii

Foreword

in high-frequency ultrasound? In my vast experi-ence as an author and editor, and my years of clinical work in musculoskeletal, neuromuscular, and elec-trodiagnostic medicine, I see Jeffrey Strakowski as the logical answer.

This volume is a refl ection of Jeff’s knowledge and dedication, and teaches the continuum of the

anatomy, clinical history and physical, electrodiag-nosis, and the ultrasound evaluation, as well as the relevance of each. This book is invaluable to anyone who has interest and is involved in diagnosis and man-agement of focal neuropathies.

Ernest W. Johnson, MD

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ix

Detailed understanding of focal neuropathies has remained a challenge in medicine and controversy often arises, particularly when optimum treatment has not been identifi ed. With technological advance-ments, high-frequency ultrasound has developed rapidly as a clinical tool, increasing roles in all areas of medicine. Assessment of peripheral nerves and focal injuries is no exception. Improving resolution and image clarity in conjunction with a growing lit-erature base has resulted in increasing value of ultra-sound in clinical scenario. Prior to the advancement of ultrasound, reliable, practical imaging of both common and unusual focal peripheral neuropathies often provided little clinical benefi t. The incorpora-tion of this modality into clinical practice can result in an increased understanding of the anatomic char-acteristics of peripheral nerves and their surround-ing structures, in both normal situations and in focal vulnerabilities. The high resolution for measuring both static and dynamic aspects of the nerve and surrounding tissue, as well as vascular fl ow, has led to capabilities for anatomic assessment like never before.

This text strives to demonstrate the value in combining the functional information gained from clinical and electrophysiologic assessments, with the anatomic correlation available with ultrasound.

Many texts propose one source of assessment over another. Electrodiagnosis and ultrasound should not be considered competitive or duplicative modalities, but instead collaborative. The goal of this volume is to promote the use of full clinical assessment, appropri-ate electrophysiologic testing, and structural evalua-tion with ultrasound in order to optimize diagnostic acumen and assist with appropriate management. Each section provides a discussion of pertinent anat-omy, clinical assessment, common electrodiagnostic tests, and the approach with ultrasound. In addi-tion, motion loops are provided with an accompany-ing DVD to facilitate understanding of the dynamic image.

The text is not designed to be all-encompassing with respect to clinical and electrodiagnostic assess-ment. It instead provides an appropriate frame-work for understanding the relative strengths and weaknesses of clinical and electrodiagnostic evalu-ations with each neuropathy, and the potential role for ultrasound. The book is structured by anatomic regions and incorporates clinical case examples dem-onstrating the value of ultrasound in each. This book is written for medical practitioners who have inter-est in gaining knowledge of the clinical approach and assessment of focal neuropathies, including the increasing value of high-frequency ultrasound. It is

Preface

ix

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Preface

x

designed to have both instructional details for less experienced practitioners as well as detailed infor-mation to be used as a reference for those with more experience.

This discipline of medicine is rapidly evolving, and improvement in techniques and understand-ing are occurring almost as rapidly as they can be

written. Feedback from colleagues with a passion for ultrasound is encouraged. I look forward to further interaction with others who have interest in ultra-sonography of peripheral nerves and other aspects of musculoskeletal and neuromuscular medicine, and remain excited about the future prospects of this technology.

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xi

This work is the result of direct and indirect contribu-tions of many individuals.

I most especially would like to thank Jay Smith, Brian Kincaid, and Joseph Ruane for their guidance in helping me get started in musculoskeletal ultra-sound nearly 10 years ago.

I would like to thank my primary mentors in electrodiagnostic medicine including Ernest Johnson, William Pease, George Waylonis, and James Powers, as well as my colleagues and mentors in our course SuperEMG (which is now UltraEMG) that includes Jun Kimura, Erik Stålberg, and Albert Clairmont. All have contributed immeasurably toward my develop-ment in this discipline.

I would like to thank Lynn Cooper, Beth St John, and the Riverside Methodist Hospital

Library for obtaining hundreds upon hundreds of manuscripts for review in preparation for this book. Their considerable effort has helped enor-mously to provide literature for review in an effi -cient manner.

I would also like to thank my staff and colleagues at Physical Medicine Associates, The McConnell Spine, Sport & Joint Center, and the residents and faculty at The Ohio State University Department of Physical Medicine and Rehabilitation who provided support and encouragement in addition to modeling many of the pictures.

I would also like to acknowledge Cadwell and General Electric, whose products were used to produce many of the images available in this book.

Acknowledgments

And fi nally, special acknowledgment and thanks to Danielle B. Guffrey, MD,for creation of the original sketches that served as the basis

for the illustrations in this book.

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65

Ultrasound evaluation of peripheral nerves and peripheral nerve pathology began being described in the late 1980s with the development of higher fre-quency transducers (Fornage, 1988). As the instru-mentation improved with advances in technology that led to higher resolution, ultrasound became the modality of choice for assessing most peripheral nerves that are not obscured by bone (Bacigalupo et al., 2003; Bianchi, 2008; Fornage, 1993).

Ultrasound can be used for diagnosis of periph-eral nerve disorders related to compression neurop-athies, trauma, and tumors (Koenig et al., 2009). In some cases, it can provide information about the type and severity of the lesion (Tagliafi co et al., 2010). It also is an ideal modality for performing peripheral nerve blocks.

EVALUATION OF PERIPHERAL NERVE

NORMAL NERVE

Anatomy

The normal nerve displays an uninterrupted fascic-ular or fi lamentous pattern, unlike the intercalated

pattern of a typical tendon (Chiou et al., 2003). Nerve fascicles are not as tightly packed as the fi bers in a tendon (Figure 4-1). Nerves have an epineurium, which is the external sheath that surrounds the nerve fascicles. Epineurium is seen as bright signal on ultra-sound and the nerve fascicles are dark (Figures 4-2and 4-3). The fascicles are enveloped by the perineu-rium. The individual fi bers are enveloped by the endoneurium. The tissue between the fascicles and the outer sheath is sometimes referred to as the “inner epineurium” and the external sheath is referred to as the “outer epineurium.”

Peripheral nerves have an extensive vascu-lar supply to provide for their metabolic needs. Large peripheral nerves are often accompanied by arteries and veins that are easily recognized with ultrasound. Nerves also have a network of ves-sels that travel longitudinally in their epineurium with branches that enter as endoneural vessels among the fascicles (Bianchi and Martinoli, 2007) ( Figure 4-4).

Peripheral nerves generally display a characteris-tic appearance with high-frequency ultrasonography. In short-axis view, nerves display a “honey-comb” appearance with hypoechoic fascicles lying inside a more hyperechoic background ( Silvestri et al., 1995)

4Ultrasound Evaluation

of Peripheral Nerves

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(A)

(B)

FIGURE 4-1 Sonograms of peripheral nerve and tendon. (A) The long-axis view of the nerve (between the yellow arrows) displays the large hypoechoic fascicles. The tendon (between the red arrows) displays the intercalated fi bular pattern. (B) The short-axis view of the nerve (yellow arrow) and tendon (red arrow). The cross-section of the fascicular pattern has the appearance of a honeycomb. The cross section of the fi ner fi bular pattern appears like the cut end of a broom.

(Figure 4-5). In longitudinal view, peripheral nerves display a characteristic fascicular pattern within multiple longitudinal hypoechoic bands of fascicular bundles. The hyperechoic bands are the intervening epineurium. The size and number of fascicles seen in nerves can be highly variable depending on the nerve size and its location in the body (Peer and Bodner,

2008). Short-axis view of the nerve is generally the best image to differentiate it from other surrounding tissue. It also assists to understand the relationship to adjacent structures. Longitudinal views provide valuable information but are more diffi cult to obtain as they frequently curve out of the fi eld of view ( Figure 4-6).


4. Ultrasound Evaluation of Peripheral Nerves

67

FIGURE 4-2 A nerve cross section. The endoneurium covers the nerve fi ber. Bundles of nerve fi bers make a nerve fascicle, which is covered by perineurium. The epineurium covers the bundles of fascicles.

Outer epineurium

Inner epineurium

Nerve fasicle coveredby perineurium

Nerve fiber coveredby endoneurium

FIGURE 4-3 Sonogram of the short-axis architecture of the musculocutaneous nerve. Note the hypoechoic fascicles surrounded by the hyperechoic epineurium.

Imaging Strategies

When it is not clear whether the structure being imaged is a nerve, the examiner should make an effort to follow its course both proximally and dis-tally (Créteur et al., 2007). This can often result in moving from an area that is more isoechoic, such as

tendon, to an area that is more hypoechoic, such a muscle, where the nerve is much easier to distinguish (Figure 4-7; Video 4-1). Toggling the transducer can also help distinguish the nerve from surround-ing tissue that has more anisotropy (Figure 4-8; V ideo 4-2). As long as the ultrasound instrument has a good resolution at faster frame rates, scanning more rapidly often creates a greater distinction between nerve and surrounding tissue than scanning more slowly (Videos 4-3 and 4-4). Using a long pathway of coupling gel along the direction of scanning can assist with rapid evaluation (Figure 4-9). Becoming familiar with characteristic bony acoustic and soft tissue landmarks can help identify various nerves (Fi gure 4-10). This includes characteristic v essels.

Attention to the pressure on the transducer is needed when scanning peripheral nerves. The soft tissue around the nerve as well as the nerve itself transforms with ex cessive transducer pressure (F igures 4-11 and 4-12; Video 4-5). Transformation of the nerve shape is particularly evident with hard p ressure when the nerve is against a hard bony struc-ture. The shape change is a result of relative fl exibil-ity of the epineurium. The perineurium is relatively infl exible and, therefore, the fascicles do not deform with routine pressure, but will redistribute inside the shape-altered epineurium. If there is focal change in



68

FIGURE 4-4 The vascular supply of a peripheral nerve. The perineural vessels run alongside the nerve and the intraneural vessels pierce the epineurium and run alongside the fascicles.

Perineuralvessel

Intraneuralvessels

the nerve shape despite only light pressure, or if there are alterations in the shape of the fascicles, then this should be considered an abnormality (Martinoli et al., 2000). Attention should be given to the amount of transducer pressure on the tissue when assessing for shape changes of the nerve. This is particularly impor-tant when performing calculations such as fl attening ratios.

Anatomic variations exist in peripheral nerves and ultrasound can be used to identify these. Knowl-edge of common anatomic variations is essential so that they are not confused with pathologic conditions. An example of a frequently cited variation is the prox-imal bifurcation of the median nerve creating a bifi d appearance (Iannicelli et al., 2000) (Figure 4-13).

Nerve Measurement

The use of perimeter tracing to determine precise cross-sectional area has been shown to be a reli-able measure that correlates with cadaver measure-ments. The cross-sectional area of nerves in short axis can be obtained by tracing with an electronic caliper around the margin of the hypoechoic nerve fascicles and inside the hyperechoic outer epineu-rium (Figure 4-14). Nerve size generally decreases when imaged from proximally to distally as the branches leave the main nerve trunk. The cross-sectional area of nerves tends to be larger in taller individuals (Zaidman et al., 2009) and smaller in women (Cartwright et al., 2007a).



69

FIGURE 4-5 Sonogram of the sciatic nerve (yellow arrow) in short axis demonstrating the “honeycomb” pattern representing the hypoechoic fascicles between the hyperechoic epineurium.

FIGURE 4-6 Sonogram of the sciatic nerve in long axis (yellow arrowheads) demonstrating the characteristic fascicular pattern of a peripheral nerve.

Nerve swelling can be measured reliably by most instruments. It is critical that the transducer be placed perpendicular to the nerve for accuracy. Measurement should be performed from the inner border of the echogenic epineurium surrounding the fascicles for consistency ( Figure 4-15). Placing the focal zone precisely at the level of the nerve

and adjusting the gray-scale mapping to optimize the contrast enhancement between the nerve and surrounding tissue, will improve precision of this measurement. It is also helpful to scan back and forth over the area of interest to more readily appreciate the tissue contrast (Créteur et al., 2004) (Video 4-6).



70

FIGURE 4-7Sonograms of the benefi t of following the nerve to a more conspicuous area when it is diffi cult to see. (A) In this case, the median nerve is more diffi cult to visualize in short-axis view at the wrist around the relatively isoechoic tendons. (B) The median nerve is more conspicuous in the region more proximally where it is surrounded by more hypoechoic muscle. Once reliably identifi ed, the nerve can be traced to the original location. Following a nerve in this fashion can assist in localization. (B)

(A)

(A)

FIGURE 4-8Sonograms of the effect of toggling the angle of the transducer to produce anisotropic effect on the surrounding tendons (red arrows), making the peripheral nerve (yellow arrow) more conspicuous. (A) The angle of the sound beam is orthogonal to the structures resulting in less contrast between them. (Continued)



71

FIGURE 4-8 (Continued)(B) The angle is changed causing more anisotropic artifact of the tendons which results in a more conspicuous nerve.(B)

FIGURE 4-9 The use of a long pathway of coupling gel to facilitate rapid scanning of the nerve.

(A)

FIGURE 4-10Examples of characteristics landmarks that can be used to identify specifi c nerves in short axis at specifi c locations. (A) The median nerve (yellow arrowhead) at the proximal portion of the carpal tunnel identifi ed by the bony acoustic landmark of the lunate (red arrow). (Continued)



72

(C)

(B)

FIGURE 4-10 (Continued)(B) The median nerve (yellow arrowhead) at its location in the distal forearm, indicated by the long-axis muscle pattern of the pronator quadratus (red arrows). (C) The location of the ulnar nerve (yellow arrow) at the mid-forearm noted by the ulnar artery (red arrow) by its bifurcation and movement away from the nerve when scanning proximally. (D) Ulnar nerve (yellow arrowhead) at the cubital tunnel. FCU 1 and 2 denote the two origins of the fl exor carpi ulnaris. (Continued) (D)



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(E)

FIGURE 4-10 (Continued)(E) C6 nerve root (yellow arrowhead) lying between the anterior tubercle (red arrow) and posterior tubercle (blue arrow) of the spinous process. (F) The fi bular nerve (yellow arrowhead) nerve at the fi bular head. (Continued)(F)



74

(G)

FIGURE 4-10 (Continued)(G) The tibial nerve (yellow arrowhead) in the tarsal tunnel. (H) The deep radial motor nerve (yellow arrowhead) pierces the superfi cial (red arrow) and deep (blue arrow) heads of the supinator. (H)



75

FIGURE 4-11 The effect of pressure from the transducer on the shape of a peripheral nerve. Note that the rounded shape of the epineurium seen in short axis on the top tracing is significantly flattened in the bottom tracing by pressure from the transducer. Note also that despite the significant change in the shape of the epineurium, the fascicle sizes are relatively unchanged by this external pressure.



76

(A)

(B)

(C)

FIGURE 4-12Sonograms of the effect of pressure from the transducer on peripheral nerves. (A) There is very light transducer pressure on the median nerve (yellow arrow) at the proximal carpal tunnel. (B) There is heavy transducer pressure. Note the relatively fl attening of the nerve (yellow arrow) by the fi rm pressure. (C) The radial nerve at the arm is seen with minimal transducer pressure. (Continued)



77

(D)

FIGURE 4-12 (Continued)(D) The radial nerve is shown with relatively heavy transducer pressure. Note the more fl attened appearance of the nerve yet more superfi cial appearance due to the compressed tissue.

FIGURE 4-13 Sonogram of a bifi d median nerve in the forearm.

FIGURE 4-14 Sonogram of the sciatic nerve (yellow arrows) at mid-thigh. Note the hypoechoic nerve fascicles (red arrow) within the hyperechoic epineurium (blue arrow).



78

(A)

(B)

FIGURE 4-15 Sonograms of proper direct measurement technique of cross-sectional area. (A) The nerve (yellow arrow) is seen in short axis. The hypoechoic nerve fascicles and hyperechoic epineurium are evident. (B) The cross-sectional area is properly measured by tracing between the hypoechoic fascicles and just inside the hyperechoic outer epineurium. (C) The measurement is performed improperly with tracing in and outside the outer epineurium. This results in an inconsistent and incorrectly increased cross-sectional area calculation. Sonograms of proper direct measurement technique of cross-sectional area. (A) The nerve (yellow arrow) is seen in short axis. The hypoechoic nerve fascicles and hyperechoic epineurium are evident. (B) The cross-sectional area is properly measured by tracing between the hypoechoic fascicles and just inside the hyperechoic outer epineurium. (C) The measurement is performed improperly with tracing in and outside the outer epineurium. This results in an inconsistent and incorrectly increased cross-sectional area calculation. (C)



79

Measurement can be done indirectly with the use of calipers, however, most ultrasound instruments have the capability of performing direct manual trac-ing and automated calculation. Manual tracing is a preferable technique to placing an overlying ellipse because many nerves have an irregular circumference, particularly at sites of entrapment (Figure 4-16).

ABNORMAL NERVE

The imaging characteristic of abnormal nerve is often related to the nature of the injury. Focal nerve entrapments typically present with swelling proximal to the entrapment site with notching at the level of c ompression (Figures 4-17 and 4-18). There is often a

(A)

(B)

FIGURE 4-16Sonograms of the varying shapes of peripheral nerves in short axis, making it diffi cult to use simple ellipse measurement for reliable cross-sectional area. All nerves are depicted by a yellow arrow or arrowhead: (A) musculocutaneous nerve in the arm, (B) radial nerve above the elbow, (Continued)



80

(D)

(C)

(E)

FIGURE 4-16 (Continued)(C) Ulnar nerve at the medial epicondyle, (D) abnormally enlarged fi bular nerve at the fi bular head, (E) sciatic nerve in the thigh, (Continued)



81

Intraneural vascularity is also an area of devel-oping interest. Nerves have a rich investment of endoneurial and epineurial vessels that have slow velocity. This can be r ecognized only rarely in some nerves with power or color Doppler Wilder-Smith 2012. Usually, no internal blood fl ow is seen with color Doppler in normal nerves, and therefore detectable fl ow signals should generally be consid-ered to represent abnormal hypervascular change (Bianchi, 2008). Color Doppler can detect increased endoneural fl ow in some entrapment neuropathies Ghasemi-Esfe et al.(2011). Studies have shown this in both median mono-neuropathies at the wrist as well as polyneuropathies (Akcar et al., 2010). Ultra-sound has not been shown to be a reliable indica-tor of the relative severity of a focal neuropathy (Moran et al., 2009), however, there are certain ten-dencies seen that are often seen with nerve injury.

(F)

FIGURE 4-16 (Continued)(F) Median nerve at the wrist, and (G) tibial nerve at the tarsal tunnel.(G)

loss of the fascicular architecture in longitudinal view and destruction of the characteristic honeycomb pattern in short-axis view with substantial injury (F igures 4-19 and 4-20). In tension neuropathy, the imaging abnor-malities can be relatively i nconspicuous. There is a multitude of theories regarding the cause of the nerve swelling in focal neuropathy. This includes blocking of axoplasmic fl ow, endoneural edema, dis-tal axonal degeneration, perineural and endoneural infl ammation, perineural fi brosis, axons sprouting, remyelination, and thickening of the perineurium and epineurium (Rempel et al., 1999).

The relative echogenicity of the nerve structure tends to decrease in pathologic states (Stuart 2004). This parameter is diffi cult to quantify precisely, but use of proximal and distal scanning as well as side-to-side comparisons can help with this assessment (Figure 4-21).



82

FIGURE 4-17 A focal nerve entrapment with swelling proximal to the compression sites and notching (yellow arrows) at the entrapment site.

(A)

(B)

FIGURE 4-18 Sonograms of a notch sign (yellow arrowheads) of the (A) ulnar nerve at the elbow and (B) median nerve at the carpal tunnel.



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FIGURE 4-19 Disruption of the fascicular architecture of a peripheral nerve seen in short-axis view. (A) The normal fascicular architecture pattern is seen. (B) The fascicles are enlarged and irregular denoting neuropathy.

(A) (B)

(A)

FIGURE 4-20 Sonograms of an ulnar neuropathy at the elbow displaying focal disruption of the fascicular architecture. (A) The short-axis view of the nerve (yellow arrow) displays enlargement of the fascicles. (B) The long-axis view displays focal contracture and echotexture change (yellow arrowheads) at the site of compression in the cubital tunnel.(B)



84

FIGURE 4-21 Sonograms of the difference in echogenicity in a pathologic state. The image on the left is of an abnormal fi bular nerve (yellow arrow) that appears hypoechoic relative to the normal fi bular nerve (red arrow) on the right.

FIGURE 4-22 Potential fi ndings with a nerve that displays conduction block. (A) The nerve appears to have focal swelling but relatively normal fascicular architecture. (B) The nerve does not appear swollen but there is a dramatically enlarged fascicle. (C) There is no discernable structural abnormality.

Neurapraxic injuries often display diffuse swell-ing with fairly preserved fascicular pattern. There is signifi cant variation seen with peripheral nerves displaying conduction block. There can be focal swelling of the whole nerve at the site of the injury, enlargement of a single fascicle or even a normal appearance ( Figure 4-22).

In axonotmesis there can also be diffuse swell-ing but there is often a loss of the fascicular pattern. Other features often seen in axonotmesis include an irregular nerve caliper as well as areas of interneu-ral fl uid or even a homogeneously hypoechoic

appearance. By contrast, an “empty bed” appearance with the retracted nerve endings occur in neurotmesis. Although it is not always easy to reliably distinguish between axonotmesis and neurotmesis on ultrasound, this remains an important role for imaging because this distinction cannot be made with electrodiagnosis before reinnervation (Tagliafi co et al., 2010).

Correlation of measurement of nerve diam-eter should also be done in longitudinal plane when assessing for pathologic swelling (Figure 4-23). Similar to abnormalities seen in tendons and muscles, abnor-malities should always be identifi ed in two planes for



85

FIGURE 4-23 Swelling of the ulnar nerve (yellow arrows) at the level of the cubital tunnel in (A) short axis and (B) at the same level in long axis. Focal nerve swelling should always be confi rmed in more than one view to avoid falsely attributing abnormality due to artifact or improper positioning.

(A)

(B)

confi rmation. For peripheral nerve evaluation, the long-axis plane is more challenging to maintain in full view, which often requires multiple measurements with movement of the transducer along its course. Short-axis cross-sectional area can be erroneously calculated if the nerve is oblique to the transducer or

if the angle of incidence from the transducer is not orthogonal to the nerve. Good correlation between the short-axis and long-axis views should be confi rmed to establish accuracy of measurement. This will also alle-viate concern for results based on artifact in an image (Figure 4-24).



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(A)

(B)

FIGURE 4-24 Demonstration of a potential source of measurement error in nerves in long axis. The image in (A) demonstrates a normal common fi bular nerve in short axis (yellow arrowhead). (B) The same nerve is seen with appropriate scanning in long axis. (C) The same common fi bular nerve is shown with the transducer moved slightly medially. Just superior to the nerve (measurement 1), the similarly hypoechoic lateral gastrocnemius muscle appears (measurement 2). If not recognized, this could potentially be misinterpreted as an enlarged nerve. Comparing the nerve appearance in two views can prevent this error. (C)



87

Use in Generalized Peripheral Neuropathies

Nerve changes are also seen in some generalized peripheral neuropathies. There is generally not great correlation with nerve swelling and clinical and electrodiagnosic abnormalities. Ultrasonography has been studied in hereditary peripheral neuropa-thies, leprosy, and some other conditions. The exam-iner should assess for both focal and fusiform nerve swelling. Ultrasound can also be helpful in identify-ing focal neuropathies within the context of underly-ing generalized peripheral neuropathy. Approaches to generalized peripheral neuropathies are discussed in more detail in Chapter 14.

INTERFACE WITH ELECTROPHYSIOLOGIC TESTING

Ultrasound is a valuable tool for overcoming chal-lenges in an electrodiagnostic laboratory. Ultra-sound can assist with confi rming accuracy of needle electrode placement in challenging muscles for both improved accuracy, and avoidance of adjacent vital structures. This is particularly useful with inex-perienced examiners (Boon et al., 2008, 2011). The anatomic clarity and dynamic visualization seen with ultrasound of muscle and nerve can provide invaluable learning experience for physicians in training and offers “hands-on” exposure previously only obtained with cadavers. Ultrasound provides

Nerve Trauma

Nerves tend to develop bulbous swelling at the level of a transection or other signifi cant injury (Figure 4-25). Ultrasound has good reliability for fi nding transected nerves (Cartwright et al., 2007b) and focal neuromas. Traumatic neuromas can sometimes be localized by palpation, however, not all neuromas create palpable tenderness and other traumatized tissue can be the source of localized discomfort. A neuroma is confi rmed with ultra-sound by identifying the well-defi ned hypoechoic mass along the path of the injured nerve (Fornage, 1988) (Figure 4-26).

FIGURE 4-25 The bulbous swelling associated with severe axonotmesis of a peripheral nerve.

FIGURE 4-26 Sonogram of a focal nerve injury from a laceration to the ulnar sensory branch distal to Guyon’s canal. Note the focal enlargement of the nerve. This is seen below the tissue scarring from the laceration (red arrows).



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localization of peripheral nerves, for both stimu-lation and recording, in better detail than surface anatomy alone. Ultrasound guidance is typically not needed by experienced practitioners to perform rou-tine nerve conduction studies. It can be helpful for challenging or small nerves that are less commonly studied. It can also be helpful for electrode placement when performing near-nerve conduction studies.

Ultrasound can also be helpful for identifying anatomic variants.

TUMORS THAT CAN AFFECT PERIPHERAL NERVES

Evaluation of tumors in and around peripheral nerves can be challenging. Knowledge of typical sites of various tumors as well as their sonographic appearances can assist in reliably characterizing some masses encountered d uring an ultrasound study (Sintzoff et al., 1992a). The use of a detailed history and physical examination remains a critical element of this assessment. MRI is often the favored imaging modality for evaluating tumors and masses. Despite this, the high resolution and Doppler fl ow

capabilities of ultrasound make it a useful modality for assessing many tumors (Bendix et al., 2005). Color Doppler is particularly helpful for determining the vascularity of tumors (Video 4-7).

Indications for imaging suspected tumors include nerve entrapment at an atypical site or sites, mass lesions, and other unusual presenta-tions of neuropathy. Imaging allows the tumor to be localized precisely as well as characterized (Figure 4-27). It is also important to identify the location of the nerve in relation to the mass. Ultra-sound cannot always reliably differentiate types of tumors, but can defi ne the relation between the mass and other tissue structures, including the nerve (Chiou et al., 2003).

If the tumor is neurogenic, ultrasound can be used to identify the parent nerve and any plexiform elements. If nonneurogenic, determination should be made on whether it is extrinsic or intrinsic. Ultrasound also helps to differentiate between cystic and solid masses and outline the size and shape. It also is an ideal modality to guide needle biopsies to obtain a his-tologic sample of the tumor. A detailed discussion of all tumors that can affect peripheral nerves is beyond the scope of this book. Intraneural and extraneural gan-glia, schwannomas, and neurofi bromas are discussed.

FIGURE 4-27 Sonogram of a mass near the radial nerve in the arm. Ultrasound is used to defi ne the characteristics of the mass including echotexture, shape, and size. The mass should also be followed in both proximal and distal directions to demonstrate any relationship to the surrounding tissue, including nerve, muscle and bone.



89

INTRANEURAL GANGLIA

Intraneural ganglia are rare and occur most com-monly at the knee and involve the fi bular and tibial nerves from the articular branches to the tibial– fi bular joint (Leijten et al., 1992). They are also seen in the suprascapular nerve at the poste-rior shoulder, ulnar nerve at the elbow, as well as the radial and median nerves. They often present as motor defi cit with pain and paresthesia (Aprin et al., 2007). Sonography of intraneural ganglia appear as other ganglia, as an encapsulated, well-defi ned, multiloculated mass that is hypoechoic or anechoic and has posterior acoustic enhancement (Lang et al., 1994; Masciocchi et al., 1992). The nerve fascicles can sometimes be seen being displaced around the mass. Although the precise source of intraneural ganglia remains controversial, growing evidence suggest that they extend from the nearby joint space through the articular branches (Spinner et al., 2003, 2008). Articular branches are small and often diffi cult to appreciate with ultrasound under normal conditions. They can often be seen with enlargement from an intraneural ganglion, and knowing the location of the articular branch leads to appropriate interpretation of this fi nding.

EXTRANEURAL GANGLIA

Extraneural ganglia reside outside of the peripheral nerve and usually arise from another portion of the nearby joint (Figure 4-28). They can sometimes cre-ate neuropathy by mass effect in tight spaces. Ultra-sound can often detect a communicating neck to the

adjacent joint or tendon sheath. Other conditions that can have a similar appearance include tenosynovi-tis, seroma, abscess, and varicose veins. Ultrasound guidance can assist with decompression of the gan-glion in real time.

PERIPHERAL NERVE SHEATH TUMORS

Schwannoma

Schwannomas, also known as neurilemmomas, are benign intrinsic nerve tumors that are derived from the level of the nerve fascicle. They appear as a round globular tumor with a speckled features (Figure 4-29). They typically present in middle age as a slow-growing solitary lesion. Characteristic locations for schwannomas include nerve roots and major peripheral nerves. Schwannomas are more common than neurofi bromas and have some characteristic differences (Table 4-1). The position of the schwannoma is usually eccentric to the nerve (Enzinger and Weiss, 1995). Schwannomas have a capsule and usually cavitation. Unlike localized neuromas, schwannomas are not usually associ-ated with syndromes such as neurofi bromatosis type 1.

On ultrasound, schwannomas appear as well-circumscribed solid soft tissue masses with features as described above (Beggs, 1999). The nerve should be seen in continuity with the mass, and scanning should be done proximally and distally to iden-tify the associated nerve. A schwannoma generally does not invade tissue but causes problems by mass effect.

FIGURE 4-28 Sonogram of a small ganglion cyst at the dorsum of the wrist (yellow arrowheads).



90

(Figure 4-30). Neurofi bromas typically present in adolescent and do not have a capsule. They typi-cally occur in groups. Plexiform neurofi bromas should be id entifi ed when possible as they t ypically cannot be resected safely.

Other Variations of Schwannomas and Neurofi bromas

Other variations of schwannomas and neurofi bromas exist. Hybrid tumors, although somewhat rare, can have schwannoma with neurofi broma (Sintzoff et al., 1992b). Schwannomatosis, a condition with multiple lesions, can occur. Also plexiform schwannomas and neurofi bromas can develop that are signifi cantly more diffi cult to resect (Korf, 1999). All of these varia-tions require suffi cient suspicion and investigation to obtain the proper diagnosis and optimize treatment.

Malignant Peripheral Nerve Sheath Tumors

Malignant peripheral nerve sheath tumors often present with worsening pain, frequently described as lancinating, as well as progressive neurologic dys-function. The symptoms and functional loss are often defi ned by their location. Malignant tumors should undergo biopsy for tissue diagnosis and staging

FIGURE 4-29 Sonogram of a schwannoma of the ulnar nerve.

TABLE 4-1 Distinguishing Schwannomas From Neurofi bromas

SCHWANNOMAS NEUROFIBROMAS

Nerve is eccentric to mass Nerve through center of mass

Has a capsule Does not have a capsule

Has cavitation Rarely has cavitation

Not associated with NF1* Localized type seen in NF1*

Malignant transformation: rare Malignant transformation: 2%

Appear in adulthood Appear in adolescence

Have more vascularity Have less vascularity

*Neurofi bromatosis type 1.

Neurofi bromas

Neurofi bromas are much less common than schwannomas and are often associated with other syndromes such as neurofi bromatosis type 1. Neu-rofi bromas are usually centered in the nerve tissue rather than eccentric to it as with schwannomas



91

ultrasound guidance for nerve blocks including perineural catheter placements (Dhir and Ganapathy, 2008; Ilfeld, 2010; Mariano et al., 2009, 2010; Neal and Chan, 2007; Niazi, 2009; Sandhu and Capan, 2002; Swenson et al., 2008). Chapter 3 discusses many of the considerations involved in the use of ultrasound for general needle guidance.

Most nerve blocks that use electrical stimulation for guidance of perineural catheter insertion advance the needle parallel to the longitudinal axis of the target nerve. By contrast, it is more conventional with ultra-sound guidance to use a needle in-plane approach to the transducer and a perpendicular nerve-to-nee-dle orientation. With ultrasound, cross-section or short-axis views allow for easier differentiation of the nerve from surrounding tissue. By maintaining in-plane orientation of the needle to the transducer, real-time needle-tip visualization and identifi cation of its location relative to the target nerve is obtained. Additionally, the subsequent perineural spread of the local anesthetic injection can be visualized with evaluation of need for needle repositioning when necessary (Gray, 2006) (Figure 4-31; Video 4-8). Some authors advocate the use of ultrasound guidance for performing incremental injections to create circum-ferential spread around the nerve and increase the rate of sensory block (Brull et al., 2011). Ultrasound has been having an expanding role in interventional procedures of this nature and is an ideal modality for therapeutic injections and blocks of peripheral nerves.

FIGURE 4-30Sonogram of neurofi bromas in the median nerve. Note that the tumors are centrally located with respect to the nerve.

before surgical resection. Ultrasound is the ideal imaging modality for performing fi ne needle aspira-tion biopsy and larger biopsies.

Other Tumors

There are other types of neural tumors that also have to be considered. This includes perineuriomas (aka localized “hypertrophic neuropathy”), adipose tumors such as fi brolipomatous hamartoma and macrodystrophia lipomatosa, as well as desmoid tumors, which are intermediate between benign and malignant (Kim et al., 2005; Lusk et al., 1987).

The history and physical examination remain an important element in the assessment of a mass, and imaging should not be considered an adequate evaluation in isolation. Other conditions such as thrombosed vessels and enlarged lymph nodes can resemble nerve tumors (King et al., 1997). Clinical evidence to confi rm the diagnosis should be sought when a nerve tumor is suspected.

ULTRASOUND-GUIDED NERVE BLOCKS

Although a detailed discussion of nerve blocks is beyond the scope of this book, an increasing body of literature is developing regarding the use of



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