Peripheral Nerve Imaging: Focus on Sonography

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
Chapter
Peripheral Nerve Imaging: Focus
on Sonography
Mohamed A.Bedewi, DanieleCoraci and SherineSwify
Abstract
The diagnosis of different peripheral nerve disorders is basically established by
electrodiagnostic tests; the assessment of the function of peripheral nerve disorders
is estimated by nerve conduction tests (NCT) and electromyography (EMG). The
need for more information about nerve morphology mandated the usage of more
diagnostic tools. This role is now achieved by means of peripheral nerve imaging
consisting mainly of magnetic resonance imaging (MRI) and ultrasonography. In
this chapter we will clarify the role of imaging in the diagnosis of peripheral nerve
disorders, concentrating more on the role of modern high-resolution ultrasound,
considering its advantages like cheap price, dynamic ability, and possibility of
comparison with the contralateral side at the same setting.
Keywords: peripheral, ultrasound, imaging, peripheral nerves
. Introduction
Diseases of the peripheral nerves are common in the setting of clinical prac-
tice. The traditional way of the diagnosis of peripheral nerve disorders is made
by neurophysiology and clinical assessment. These tools give information about
the functional status of the involved nerve, the presence of nerve damage, and
the degree of demyelination [1]; however, the need for more information about
nerve morphology mandated the usage of more diagnostic tools. This role is now
enhanced by means of peripheral nerve imaging consisting mainly of magnetic
resonance imaging (MRI) and ultrasonography, with special ability to assess small-
sized and difficult nerves [2].
. Magnetic resonance imaging
Magnetic resonance imaging is a noninvasive imaging technique that has the
ability to differentiate pathological peripheral nerves from healthy ones. MRI is also
useful in the demonstration of the topographic anatomy of the peripheral nerves.
MRI uses a strong magnetic field to create a net magnetization in the involved
tissues, then disruption of this magnetization with pulse, and change of direction
resulting in T1- and T2-weighted images. Basic MRI study of the peripheral nerves
uses T2-weighted images (with fat suppression) detecting the site of injury as sharp
hyperintense (as a result of local edema), in comparison to the nearby healthy
nerves which appear as isointense. As nerve regeneration resumes, the degree of
hyperintensity will gradually return to isointesntiy. Fat suppression is used for

Peripheral Nerves - Injuries, Disorders and Treatment

better visualization. Typically a 1.5 Tesla machine is used, with better results if a
stronger magnet is utilized (3 Tesla). As a result of research, a newer MRI technique
was developed, which is diffuse tensor imaging (DTI), tracking the diffusion
of water molecules, depending on the fact that there is a difference in diffusion
pattern between the healthy and injured nerves. The healthy nerves appear as
linear structures which maintain diffusion in an anisotropic pattern restricting the
movement linearly. If there is structural damage, the water molecules diffuse in an
orthogonal pattern [3–5]. Among the disadvantages of MRI are the high-cost and
long examination time. Also MRI is not tolerated by claustrophobic patients, and
the examination is not suitable for patients with pacemakers and many types of
surgical implants.
. Ultrasound
The first report of nerve ultrasound was by Bruno Fornage in the year 1988,
who used a linear transducer with a 5–7.5 MHZ frequency. Ultrasound is a cheap
modality, which allows examination of the whole nerve at the same setting, plus the
contralateral side [2]. This modality is also dynamic, with excellent spatial resolu-
tion and nonionizing radiation and good patient compliance. Among the disadvan-
tages of ultrasound is that the procedure is operator dependent, limited ability to
visualize deep nerves and long learning curve [3]. Initially ultrasound was mainly
used to assess the cross-sectional area (CSA). Among the additional parameters
assessed by peripheral nerve ultrasound is the so called “nerve density,” represent-
ing hypoechoic/hyperechoic ratio [6]. The use extended field of view is sometimes
needed.
. Ultrasound exam and findings
In order to perform an accurate examination, a good knowledge of the anatomi-
cal landmark of each nerve is essential. A linear high-frequency transducer 5–18
MHZ (Figure ) is used for ultrasound examination. Another transducer (Hockey
stick) is occasionally referred to (Figure ). Peripheral nerves should be imaged in
both short and long axes; they appear in short axis as hypoechoic structures with
peculiar fascicular pattern “honeycomb appearance.” We recommend beginning the
examination in short-axis scan, as differentiation of the nerves is difficult from the
surrounding longitudinally oriented structures like tendons.
Topographic anatomy is always helpful in identifying specific nerves. The probe
position must be placed perpendicular to scanned nerve in order to avoid anisotropy
phenomenon. The simplest measurement of nerve caliber is made by estimating
the cross-sectional area (CSA). Two known methods are used for this purpose, the
older of which is the ellipse technique, and the newer and most recommended one is
the tracer method, by which the nerve is measured inside the hyperechoic epineu-
rium. Each nerve has a reference value, which when exceeded is a sign of disease.
Loss of the fascicular pattern could be a sign of disease, as a result of edema/conges-
tion. The cause is variable, the most important of which is compression neuropathy.
Other types of neuropathies also exist like immune-mediated neuropathies. The
role of ultrasound in traumatic injuries is quiet important. The most important
issue in trauma is to make sure of nerve continuity, and if there is an injury, it is
complete or partial [7–12]. New techniques like three-dimensional imaging and
compound imaging were developed during the last 10years. Measurement of stiff-
ness of the nerve is established by elastography [6].

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Peripheral Nerve Imaging: Focus on Sonography
DOI: hp://dx.doi.org/10.5772/intechopen.89742
. Brachial plexus
The brachial plexus consists of the network of nerves providing the sensorimo-
tor supply of the upper limb (C5-T1) (Figure ) [6]. Brachial plexus injuries are
common in different types of trauma, including car accidents and falls, which could
lead to severe impairment. Some lesions are minor, and patients could recover with-
out surgery. The presence of a good diagnostic tool is essential in this manner [13].
Brachial plexus lesions are common, whether traumatic or nontraumatic. Traumatic
lesions could also be open or closed.
. Upper limb nerves
The radial nerve arises from the C5–C8 nerve roots. This nerve has a peculiar
spiral course around the humerus, maintaining direct contact with the humerus,
making the nerve highly sustainable to trauma (Figure ). At the distal upper arm,
the radial nerve divides into superficial (mainly sensory) and deep (mainly motor)
branches (Figure ). The ulnar nerve (Figure ) arises from C8-T1nerve roots.
Figure 1.
Linear transducer.
Figure 2.
Hockey stick transducer.

Peripheral Nerves - Injuries, Disorders and Treatment

Two common levels of injury/entrapment to the ulnar nerve are the cubital tunnel
(Figure ) at the level of the medial epicondyle of the elbow joint (which represents
Figure 5.
A case of blade trauma in the forearm. The patient presents with plegia of the extensor digitorum communis
muscle. From right to left, the images show the posterior interosseous nerve course from proximal to distal. In
the image at the center, the nerve is not visible (ellipse), while proximally (right) and distally (left), the nerve
is depictable (arrows).
Figure 3.
Short-axis scan of the C5, C6, and C7 nerve roots, in the interscalene groove, between the middle scalene and
anterior scalene muscles. s, scalene muscle.
Figure 4.
A case of upper limb trauma with humeral bone fracture and following deficit in finger extension. The
posterior interosseous nerve is larger than the contralateral side.


Peripheral Nerve Imaging: Focus on Sonography
DOI: hp://dx.doi.org/10.5772/intechopen.89742
Figure 6.
Short-axis scan of the ulnar nerve at the forearm.
Figure 7.
Short-axis scan of the ulnar nerve at the cubital tunnel.
Figure 8.
Short-axis scan of the ulnar nerve (UN) at Guyon’s canal. PISI.Pisiform bone; UA, ulnar artery.

Peripheral Nerves - Injuries, Disorders and Treatment

one of the common compressive neuropathies) and at Guyon’s canal at the level of
wrist joint (Figure ). The median nerve is the most important nerve of the upper
limb. It arises from the C6-T1 nerve roots. The median nerve is also the easiest nerve
Figure 9.
Short-axis scan of the median nerve at the carpal tunnel.
Figure 10.
Long-axis scan of the median nerve at the carpal tunnel.
Figure 11.
Short-axis scan of the median nerve at the carpal tunnel with increased CSA.

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Peripheral Nerve Imaging: Focus on Sonography
DOI: hp://dx.doi.org/10.5772/intechopen.89742
scanned in the body. The commonest entrapment syndrome is related to this nerve
when it entraps in the carpal tunnel level, the so called “carpal tunnel syndrome.”
Good knowledge about congenital anatomical variation is essential (Figures –)
[14, 15].
. Lower limb nerves
The sensorimotor supply of the lower limb is derived from the lumbosacral
plexus. The most important nerves of the lower limb are the sciatic nerve, the femo-
ral nerve, the common fibular nerve, and the tibial nerve. Two other nerves could
be added but are less important which are the saphenous nerve and the sural nerve.
The femoral nerve could be injured during surgical/interventional procedures, and
it gives branch to the saphenous nerve which also could be injured during varicose
vein stripping operations due its close proximity to the long saphenous vein. The
sciatic nerve is the largest nerve in the human. This nerve is practically a combina-
tion of the two nerves, the tibial and the fibular nerve with one common sheath.
Actually the level of true division of the sciatic nerve into these nerves is highly
variable in the human population (Figures –) [14, 16].
. Traumatic peripheral nerve injuries
Trauma to the peripheral nerves could be direct or indirect; one of the following
consequences could happen. Structural and morphological changes could occur,
resulting in change in the echogenicity or the shape of the nerve. Most of the stud-
ies take Sunderland classification as a reference to in dealing with the degree of
Figure 12.
Bifid median nerve at the level of the carpal tunnel.
Figure 13.
Short-axis scan of the common fibular nerve.

Peripheral Nerves - Injuries, Disorders and Treatment

post-traumatic peripheral nerve lesions. Penetrating injuries could lead to partial or
complete cut of the nerve (transection), with associated laceration. One of the most
important changes is nerve contusion and/or compression. Repetitive insults could
lead to stretch along the course of the nerve. Ultrasound does not clearly demonstrate
endoneurium but clearly visualize perineurium and epineurium. Also ultrasound
could well demonstrate fascicular anatomy but not myelin and axonal anatomy [17].
In conclusion, the main role of ultrasound in the assessment of traumatic nerve lesions
is to assess the continuity of the nerve and presence of axonotmesis or neurotmesis
and also assessment of other sites of injury and, in some cases, the cause of injury.
Abbreviations
NCT nerve conduction test
EMG electromyography
Figure 14.
Photo of scan of the sural nerve at the lateral aspect of leg.
Figure 15.
Short-axis scan of the sural nerve at the lateral aspect of the leg.

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Peripheral Nerve Imaging: Focus on Sonography
DOI: hp://dx.doi.org/10.5772/intechopen.89742
Author details
Mohamed A.Bedewi1*, DanieleCoraci2 and SherineSwify3
1 Department of Internal Medicine, Prince Sattam Bin Abdulaziz University,
College of Medicine, Alkharj, Kingdom of Saudi Arabia
2 Fondazione Policlinico A.Gemelli IRCCS, Rome, Italy
3 Ministry of Health and Population, Alexandria, Egypt
*Address all correspondence to: mohamedbedewi@yahoo.com
MRI magnetic resonance imaging
DTI diffuse tensor imaging
CSA cross-sectional area
© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms
of the Creative Commons Attribution License (http://creativecommons.org/licenses/
by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,
provided the original work is properly cited.


Peripheral Nerves - Injuries, Disorders and Treatment
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