In my work as a sonographer and beside the general sonography, pediatrics, 

and MSK, I do scan lots of peripheral nerves for pathology and also to mark the sites

for the radiologist to administrate the cortisone or other injections.

Some of the nerves that I deal with are the ulnar and radial nerves, carpal tunnel and

Guyon’s canal area, sciatic nerve and piriformis muscle area, lateral thigh cutaneious nerve,

genitofemoral nerve , tibial nerve, peroneal nerve, Morton neuroma, among others.

and Ultrasonography are a first-line modality for evaluation of the peripheral nerves

of the upper extremity. A detailed knowledge of anatomic landmarks

facilitates assessment of the peripheral nerves with Ultrasound.

With improvements in ultrasound (US) imaging equipment and refinements

in scanning technique, an increasing number of peripheral nerves and

related pathologic conditions can be identified.

Ultrasonography (US) has become a first-line modality for the evaluation of the

peripheral nerves of the upper extremity. The benefits of US over magnetic resonance

(MRI) imaging include higher soft-tissue resolution, cost effectiveness, portability,

real-time and dynamic imaging, and the ability to scan an entire extremity quickly and efficiently.

Modern Ultrasound imaging supports the clinical examination and

electrophysiological testing in setting the diagnosis, and enhances this information

by illuminating the morphological aspects and etiology of peripheral nerve pathology.

 Ultrasonography can readily be used for detection of nerve abnormalities caused by

trauma, tumors, inflammation and a variety of non-neoplastic conditions,

including compressive neuropathies.

It is important for the radiologist or sonographer to have a detailed knowledge of

anatomy and specific anatomic landmarks for each nerve to efficiently and accurately

perform an examination. The goal of this article is to introduce readers to the basics of US

of the peripheral nerves of the upper extremity with a focus on the median, ulnar,

and radial nerves. Common sites of disease and the location

of important anatomic landmarks will be reviewed.

 Well recognized advantages of the method such as the possibility of a dynamic

examination, assessing long nerves segments in a short time, bed-side-availability,

non-invasively and low cost, make US the ideal imaging tool in peripheral nerve disease.

Ultrasound can be performed on patients who are not eligible for MR imaging.

Metallic implant artifacts are usually not problematic. US has been shown to

have equal specificity and greater sensitivity than MR imaging in the evaluation of peripheral nerves.

For superficial nerves (e.g. median nerve in the carpal tunnel or ulnar nerve at the elbow)

the maximum frequency (up to 18 MHz) can be applied.

Due to the limitation of the penetration depth of high frequencies, in deeper lying

nerves or nerve segments (e.g. median nerve at the proximal forearm or sciatic nerve), lower frequencies

 (Down to 5 MHz) are required. With low ultrasound frequencies,

the resolution is worse and the differentiability of the nerves in the surrounding

tissue as well as of their internal structure becomes difficult. Good ultrasonic devices

allow up to a depth of about 2.5 cm also an assessment of subtle changes.

Common indications for upper extremity peripheral nerve US are the evaluation for

injury due to penetrating trauma, entrapment by scar tissue, and tumor. US of the upper

extremity are most commonly performed to evaluate carpal and cubital tunnel syndrome.

In addition to a high physical resolution, the soft tissue contrast in particular,

is decisive for optimal visualization of the peripheral nerves. Special software, e.g.

‘‘compound- imaging’’, ‘‘high-resolution-imaging’’, is very helpful in this process.

Additional tools, e.g. extended field of view imaging, which create a panorama image

from numerous individual images, can improve image documentation.

Any abnormal findings can be easily compared with the contra lateral side.

The published literature has shown that US has demonstrated clinical utility in patients with

suspected peripheral nerve disease by guiding diagnostic and therapeutic decisions as

well as by confirming electro diagnostic findings

The application of color-coded sonography (color Doppler or power Doppler)

allows assessing the vascular situation of the nerves and their surroundings.

This is particularly useful in inflammatory conditions, nerve tumors or compressive neuropathies.

Color coded sonography is also helpful in localizing nerves that are often accompanied

by vessels (e.g. radial nerve at the lateral upper arm accompanied by the profound

brachial artery; sural nerve accompanied by a vein).

 For color Doppler, a small-flow-setting of the ultra- sound device is recommended

(pulse repetition frequency 500 Hz, band-pass filter 50 Hz). It is important to notice

that an exploratory study, even without high-end ultrasound equipment, can detect major

changes, such as severe nerve compression or a mass lesion.

 For the assessment of fine structures or complex changes, such as in post-operative

conditions or nerve injuries, however, high-quality equipment is required.

In addition to the operative equipment a good knowledge of the regional topographic

anatomy is Important. Further, the examiner’s expertise in diseases of the peripheral nervous

system and electrophysiological knowledge facilitate the interpretation of NUS.

The typical examination of peripheral nerves begins with transverse sections.

The nerve is initially visualized at a site with typical anatomical landmarks

(e.g. median nerve in the carpal tunnel, ulnar nerve in the sulcus).

After image optimization, the nerve can be followed further continuously in the proximal

and distal directions, and in the area of suspected pathology.

The site of underlying pathology is normally located in transverse sections,

for a more precise information longitudinal scans and the examination of vascularization

with color coded sonography are performed.

What nerves can be examined?

In normal-weight people, all major nerves of the extremities, e.g. the median,

ulnar, radial, sciatic, tibial and peroneal nerves,

can be visualized in their entire course at the extremities.

Even smaller nerves, e.g. the interosseous posterior and the superficial radial nerve,

are regularly displayed. The spinal nerves C4-C8 and the supraclavicular

brachial plexus can also be visualized, but especially the inferior trunk and

the fascicles are not constantly imaged in good quality.

The visualization of the infraclavicular and infrapectoral brachial plexus is

restricted by the clavicle and the depth of the structures. Cranial nerves like

the vagal and accessory nerves, can be visualized regularly. Particularly in

obese patients, the examination of the sciatic nerve in the thigh and tibial

nerve at the proximal lower leg is difficult or even impossible.

In lean people, however, even small sensory nerves, such as the saphenous,

sural and superficial peroneal nerve as well as the lateral femoral cutaneous nerve can be assessed.

Sonography of healthy peripheral nerves

The nerves are cable-like structures that appear on transverse sections as round

to oval hyperechoic structures they are surrounded by an echogenic rim representing

the epifascicular epineurium and the perineurial fatty tissue.

The sonographic echo pattern (echo texture) is called ‘‘honeycomb-shaped’’.

The rounded hypoechoic areas correspond histologically to the nerve fascicles,

and the echogenic septa to the interfascicular epineurium.

Areas correspond histologically to the nerve fascicles,

and the echogenic septa to the interfascicular epineurium.

Pathological findings

Frequent entrapment sites in the upper extremities

E.g. the carpal tunnel (median nerve), the cubital tunnel and the Guyon’s canal

(ulnar nerve), and the supinator tunnel (interosseous posterior nerve).

In the lower extremities

Peroneal nerve at the fibular head, tibial nerve in the tarsal tunnel,

the interdigital nerves (Morton-Metatarsalgia) and the lateral femoral cutaneous nerve can be examined.

The basic diagnostic criterion is the visualization of nerve compression,

which appears regardless of anatomic location on longitudinal scans as an

abrupt flattening (notching) at the site of nerve compression

and a fusiform swelling proximal and distal to it.

The swelling is accompanied, depending on the degree of compression,

by a hypoechogenisty and a reduction of visibility or extinction of the typical fascicular

echo- texture resulting of nerve edema.

The sonographic findings thus reflect the path morphological changes in terms of

nerve constriction at the site of compression and the pseudo neuroma formation.

In addition, NUS allows evaluation of the surrounding structures and

finding nerve compression etiology, e.g. compression by a mass lesion.

Anatomical variations can be evaluated as well. Thus, NUS helps in planning

and timing of further therapy (conservative / operative, e.g.

in case of compression by a mass lesion early surgical therapy).

Carpal Tunnel syndrome

Carpal tunnel syndrome (CTS) is the most common peripheral nerve

disorder with a lifetime prevalence of about 15%. In typical cases the longitudinal

scans show a nerve compression under the flexor retinaculum with the

formation of a pseudo neuroma proximally and (often to a lesser extent) distally to the retinaculum

Scan the nerve in a transverse section

It will show you the nerve area and any other measurement you want to measure.

Then take a picture of the enlargement at the site of pseudo neuroma,

which is quantified by cross-sectional area measurements

at the level of the carpal tunnel inlet (pisiform bone).

You also scan proximal to the median nerve at the pronator quad muscle

, then distal and under the flexor retinaculum. 

In seldom cases, an enlargement at the carpal tunnel outlet only can be seen.

NUS have a sensitivity (from 73% to 92%) and specificity comparable to

electrophysiological methods. Further, NUS represents a complementary

method to the electrophysiological evaluation. 

Even with normal electrophysiology NUS can detect pathological findings,

and vice versa. An even more important contribution of NUS is to rule out

secondary CTS that includes tenosynovitis of the flexor tendons, ganglia,

arthritic changes, amyloid deposits, accessory muscles or median artery

thrombosis Furthermore, anatomical variants such as prolonged muscle belie

of the finger flexors reaching into the tunnel, can be detected.

More important are nerve variants such as

Bifid median nerve divided into two strands already in the carpal tunnel or

variants of the thenar branch (subligamentary or transligamentary course).

Also, vessel variants like a persisting median artery or atypical course of the ulnar artery, can be seen.

The detection of such normal variants can be significant especially for

the endoscopic surgeon. In every third patient with CTS, sonography

found one of the above-mentioned structural abnormalities.

Therefore, contrary to the prevailing opinion, CTS cannot be regarded as an

idiopathic condition. NUS play a very important role in postoperatively persisting

or recurrent CTS. It allows visualization of surgically treatable causes like

incomplete retinaculum transaction with persistent nerve compression or

surgery complications such as abnormal scarring or iatrogenic nerve injury.

Based on personal experience, sonography can reveal a false preoperative

diagnosis showing conditions mimicking CTS like nerve tumor or neuritis.

Ulnar neuropathy at the elbow

Ulnar neuropathy in the elbow region (UNE) comprises three entities with

their own etiology, and therapy. The cubital tunnel syndrome represents the

most common disorder. Its pathological basis is a nerve compression under

the aponeurosis between the origins of the ulnar flexor muscle of the wrist (humeroulnar arcade).

Correspondingly, ultrasound shows a flattening of the nerve under

the arcade with a proximal swelling in the sulcus. Cross-sectional areas greater

than 0.1 cm2 accompanied by a hypoechoic appearance and loss of the honeycomb

echo texture, are diagnostic for cubital tunnel syndrome. Another entity is caused by

a repetitive subluxation or luxation of the nerve out of the sulcus leading to chronic pressure damage.

A lacking or loose humeroulnar arcade is postulated as a reason for this.

In the case of subluxation, the ulnar nerve is located at the tip of the medial epicondyle

at maximum elbow flexion. In the case of luxation, it is dislocated volar to the medial epicondyle.

The nerve dislocation is often accompanied by a nerve swelling.

Further, space-occupying lesions such as ganglia, lipomas, arthritic changes

accessory muscles, or a dislocation of the medial triceps head

(‘‘snapping triceps syndrome’’) can be reliably identified.

In these cases, the compression is often located proximal to the cubital tunnel,

which may result in atypical electrophysiological findings.

The diagnostic value of sonography is comparable with electrophysiological methods;

in combination it improves the diagnostic yield.

In addition, it provides prognostic information: the extent of swelling

in the sulcus correlates negatively with clinical improvement after surgery

less common compression syndromes since the less common compression

syndromes affect mostly smaller nerves, the sonographic

depiction of a direct nerve compression is more difficult.

Therefore, the main role of sonography lies in the recognition of neighborhood.

Thus, sonography can detect space-occupying lesions such as ganglia or

lipomas affecting the ulnar nerve in Guyon’s Loge, the medial processes as

compression factors nerve at the proximal forearm, the interosseous

posterior nerve in the supinator tunnel, the axillary nerve in

the quadrilateral space as well as the suprascapular nerve.

In the so-called algetic interosseous-posterior-syndrome an

ultrasound-guided infiltration can be performed for diagnostic purposes.

In thoracic-outlet-syndrome, sonography can reveal a compression of the spinal nerve

C7 or C8 by a cervical rib. In the lower extremities, peroneal nerve at the fibular head

and tibial nerve in the tarsal tunnel can be affected by different soft tissue masses

(enlarged bursae, ganglia, heterotopic ossification after trauma).

Especially the peroneal nerve can be affected by intraneural ganglia emerging

from tibiofibular joint via the articular branch.

 In Morton’s Metatarsalgia a ‘‘neuroma-like enlargement’’

of the second or third plantar interdigital nerve can be seen. Even in obese patients

with meralgia paresthetica, a compression of the lateral femoral cutaneous nerve

can be demonstrated and combined with an ultrasound-guided infiltration (personal experience).

Sonography of peripheral nerve tumors

The diagnosis of peripheral nerves with ultrasound was described in literature

back in the 1980s. This was possible because large nerve tumors could be detected

even with older transducers with a low scanning frequency (around 7 MHz).

The two most common types of tumors are schwannomas (neurinoma) and neuro fibromas.

Sonographically, both appear as well-defined, round masses with a hyperechoic rim,

which are localized in the course of a peripheral nerve.

Schwannomas are mostly homogeneously hypoechoic and lie eccentric to the

long nerve axis, in contrast to neuro fibromas, which lie central. Neurofibroma ‘s echogenicity

is higher and distributed in the center of the mass (so called target sign).

Schwannomas show often a hypervascularization in color coded examination,

in Neurofibroma’s no significant internal perfusion can be seen even in contrast enhanced ultrasound.

Plexiform Neurofibroma’s, which occur typically in neurofibromatosis type

1-(von Recklinghausen’s disease), spread over long segments of one or more nerves.

The nerves are infiltrated with small nodules which form a dysmorphia mass

of heterogeneous echogenicity uplifting the inner nerve architecture (‘‘sack full of worms’’).

Peri-neuromas are generally less well known. They appear often in young patients

and present with painless progressive motor deficits. With NUS they appear as

fusiform hypoechogenic structures without vascularization spreading over several centimeters.

Genitofemoral nerve block.

Ultrasound-guided genitofemoral nerve block is utilized as a diagnostic

and therapeutic maneuver in the evaluation and treatment of groin and inner

thigh pain thought to be mediated via the genitofemoral nerve.

The patient is positioned supine, and a linear ultrasound probe with high frequency

(6–13 MHz) is used. Initially, the probe is placed in the transverse plane

below the inguinal ligament. In this plane, the femoral artery

is identified and positioned in the middle of the screen.

The probe is then rotated so the artery lies in the long axis. The ultrasound probe is

then moved cranially to trace the femoral artery until it dives deep into the abdomen

to become the external iliac artery. At this point, an oval or circular

structure may be seen superficial to the femoral artery.

This structure is the inguinal canal, which contains the spermatic cord

in men and the round ligament in women. The probe may be moved slightly medial

to trace the spermatic cord or round ligament. In males, arterial pulsation

s may be visible within the spermatic cord. These pulsations represent

the testicular artery and the artery to the vas deferens and may

be confirmed by the use of color Doppler.

The blood vessels may be made more prominent by asking the patient to perform a

Valsalva maneuver, which increases blood flow through the pampiniform plexus.

In addition to the arteries, a thin tubular structure within the spermatic cord may

also be visible; this is the vas deferens. In females, the round ligament can be

difficult to visualize, and the target is the inguinal canal.

A sonographic screening examination for the presence of nerve tumors should be

performed in every etiologically unexplained neuropathy. The affected nerve has to

be visualized in its entire also possible without high-quality technical equipment.

Generalized neuropathies (polyneuropathies) in generalized neuropathies,

ultrasonography is not routinely used yet. 

In a variety of diseases, however, NUS can demonstrate a generalized enlargement

(edema) of the peripheral nerves, e.g., in acromegaly, or diabetes mellitus,

which explains the frequent occurrence of entrapment syndromes.

A generalized nerve hypertrophy is also found in hereditary neuropathies (

e.g., HMSN). In immune-mediated inflammatory neuropathies (e.g., AIDP, CIDP, MMN),

a so-called hypertrophic remodeling of the peripheral nerves is present

It is characterized by nerve hypertrophy and a variation of individual fascicle

thickness changing in the nerve course (personal experience).

Focal nerve or fascicle thickening can also be found in painful mononeuropathies

with a possibly immunologic etiology. Sonography can also differentiate

nerve compression syndromes in polyneuropathies, which is particularly

difficult with electrophysiological methods.

Sonography of traumatic nerve lesions

Sonography has an important role in the assessment of traumatic neuropathies.

For the investigation is a high- quality equipment of great benefit,

since it facilitates the presentation of changes in difficult conditions

with tissue edema, hematomas, and scars.

NUS can assess the continuity and integrity of the nerve,

characterize the defect, and identify secondary nerve compression.

Thereby, location, extent and type of damage are determined.

This allows displaying a complete and partial nerve transaction, the distance

and condition of the stumps (formation of a neuroma) or a compression of the nerve,

for example, by scars, ostheo-synthetic material, callus formation,

bone fragments, hematomas, or foreign bodies .

The most frequent Ultrasonography of the peripheral nervous system alteration

found in nerve trauma is axonal swelling the nerve and its fascicles will shows

a hypoechoic thickening over several centimeters, in proximal limb lesions sometimes,

sometimes focal and sometimes affecting the whole extremity.

In severe traumas, axonal swelling persists over several months and diminishes

from proximal to distal with the forthcoming reinnervation (personal experience).

Sonography allows differentiating major nerve trauma that requires

surgical therapy, i.e. a complete and partial nerve neurotmesis.

Since the degree of stump dehiscence determines the surgical procedure

(neurorrhaphy in the case of a small defect, nerve transplant in the case of greater dehiscence),

the distance of the nerve stumps should be measured.

In Sagittal scans an amputation neuroma appears as a hypoechoic thickening or

a bulbous mass where the nerve ends. In the case of a partial nerve transaction,

also intact parts of the nerve and its interfascicular epineurium can be scanned.

This type of lesion is very difficult to diagnose with clinical and electrophysiological

methods especially in the early post-traumatic period (within 3 months).

Neuroma-in-continuity is represented by a fusiform hypoechoic thickened nerve

with extinctic nerve echotexture. Thus, NUS can facilitate the therapeutic decisions

and initiate early surgical intervention using the appropriate method

(neurorrhaphy, nerve grafting or neurolysis).

Postoperative complications such as dehiscence of the nerve

sutures or abnormal scarring can be identified, too.

Malignant peripheral nerve sheath tumors are a rare type of cancer that

occurs in the lining of the nerves that extend from the spinal cord into the body.

Malignant peripheral nerve sheath tumors used to be called neurofibrosarcomas.

Malignant peripheral nerve sheath tumors can occur anywhere in the body,

but most often occur in the deep tissue of the arms, legs and trunk

. They tend to cause pain and weakness in the affected area and

may also cause a growing lump or mass.

Malignant peripheral nerve sheath tumors are typically treated with surgery.

In certain cases, radiation therapy and chemotherapy also may be recommended.

Some of the nerve tumors include.

Acoustic neuroma

also known as vestibular schwannoma, is a noncancerous and usually

slow-growing tumor that develops on the main (vestibular) nerve leading from

your inner ear to your brain. Branches of this nerve directly influence your balance and hearing,

and pressure from an acoustic neuroma can cause hearing loss,

ringing in your ear and unsteadiness.

Acoustic neuroma usually arises from the Schwann cells covering this nerve

and grows slowly or not at all. Rarely, it may grow rapidly and become

large enough to press against the brain and interfere with vital functions.

Benign peripheral nerve tumors

Affect nerves by growing within them or by pressing against them.

Peripheral nerve tumors that grow within nerves are called intraneural tumors.

The tumors that press against nerves are called extraneural tumors.

Most are benign, meaning that they are not cancerous. Different types

of benign peripheral nerve tumors include:

Schwannoma. The most common benign peripheral nerve tumor in adults,

a schwannoma can occur almost anywhere on the body. 

These nerve sheath tumors are called schwannomas because they are made up

of Schwann cells, which are cells that surround the nerves.

These tumors usually grow slowly. If you develop a schwannoma in an arm or leg,

you might notice a mass. But you might have a schwannoma for years before noticing it.

A schwannoma typically comes from a single bundle of nerve fibers,

called a fascicle, within the main nerve. Some schwannomas grow and form unusual

shapes within the spine or pelvis, such as dumbbell tumors. When a schwannoma

grows, more fascicles are at risk when trying to remove the tumor safely.

Schwannomas most commonly occur alone. Occasionally some people have

several of them in the arms, legs or body. This is a condition called schwannomatosis.

Neurofibroma 

This common type of benign nerve tumor tends to form in the center of a nerve.

A neurofibroma might arise from several nerve bundles and tends to cause mild symptoms.

This tumor most commonly develops in people who have neurofibromatosis 1 (NF1).

This is a genetic disorder that causes tumors to grow on nerves.

Perineurioma 

This rare benign peripheral nerve tumor arises from perineurial cells,

a type of cell that surrounds the peripheral nerve sheath.

A perineurioma can form within a nerve, called an intraneural perineurioma.

It may also form in soft next to a nerve, called an extraneural perineurioma.

An intraneural perineurioma happens most often in children and young adults.

It typically causes gradually progressive weakness and loss of feeling in an arm or leg.

Lipoma

Slow-growing fat cells cause this benign, soft lump that usually appears under

the skin on the neck, shoulders, back or arms. A lipoma near a nerve can squeeze it.

Usually, though, a lipoma causes no pain or other problems. Your health care provider

might want to monitor a lipoma through regular checkups.

Ganglion cyst. 

Some ganglion cysts come from an injury, but most have no known cause.

They commonly form near joints, such as the wrist, and can cause pain

and interfere with everyday activities. Some go away without treatment,

but ganglion cysts that press neighboring nerves should be removed.

Desmoid tumors are noncancerous growths that occur in the connective tissue.

Desmoid tumors most often occur in the abdomen, arms and legs.

Another term for desmoid tumors is aggressive fibromatosis.

Some desmoid tumors are slow growing and don’t require immediate treatment.

Others grow quickly and are treated with surgery, radiation therapy, chemotherapy or other drugs.

Desmoid tumors aren’t considered cancers because they don’t spread to

other areas of the body. But they can be very aggressive, acting more like cancers

and growing into nearby structures and organs. For this reason,

people with desmoid tumors are often cared for by cancer doctors.

Conclusion

Ultrasound is a valuable tool for imaging peripheral structures, guiding needle advancement,

and confirming the spread of injectate around the target tissue,

all without exposing healthcare providers and patients to the risks of radiation.

The complete diagnosis of peripheral nerve damage includes not only the evaluation

of nerve function with clinical and electrophysiological methods,

but also the assessment of nerve morphology with imaging methods.

In patients with chronic pelvic pain, the target structures for interventional procedures can

be well visualized with the use of ultrasound. Most of the ultrasound-guided interventional

procedures for chronic pelvic pain have been validated and thus can be accurately performed.

Sonography allows not only to set the diagnosis, but also to reveal the etiology of the condition.

Hence, early and appropriate therapeutic measures can be derived.

Sonography can be used as the screening imaging tool for

all disease categories of the peripheral nervous system.

Steve Ramsey, PhD.