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Published online August 25, 2003, 10.1148/rg.e15
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(Radiographics. 2003;23:e15.)
© RSNA, 2003

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Peripheral Nerve Lesions: Role of High-Resolution US1

Hong-Jen Chiou, MD, Yi-Hong Chou, MD, See-Ying Chiou, MD, Ji-Bin Liu, MD and Cheng-Yen Chang, MD

1 From the Department of Radiology, No. 201, Sec 2, Shih-Pai Rd, Taipei-Veterans General Hospital and School of Medicine, National Yang Ming University, Taipei, Taiwan (H.J.C., Y.H.C., S.Y.C., C.Y.C.); and the Institute of Ultrasound, Thomas Jefferson University Hospital, Philadelphia, Pa (J.B.L.). Presented as an educational exhibit at the 2002 RSNA scientific assembly. Received April 29, 2003, revision requested July 2, revision received and accepted July 7. Address correspondence to H.J.C. (e-mail: hjchiou@vghtpe.gov.tw).


   Abstract
Top
 Abstract
Introduction
 Sonohistology
 Scanning Techniques
 Abnormalities
 Conclusion
 References
 
The peripheral nerve is demonstrated as a reticular pattern in a transverse section at high-resolution ultrasonography (US). Its echogenicity is between that of tendon and muscle. High-resolution US applied to lesions of peripheral nerves yields impressive results in that the nerve is highly differentiated from surrounding soft tissue. In cases of trauma, high-resolution US can easily differentiate between a rupture of the nerve bundle and fibroblast infiltration that results in traumatic neuroma. In cases of inflammation or compressive syndrome, high-resolution US can easily demonstrate lesion location and cause. In the evaluation of abnormal masses, high-resolution US cannot clearly differentiate neurofibromas from schwannomas but it can clarify the relationship between tumor and neural trunk and help the clinician plan treatment strategies. The authors discuss the success that can be achieved with the application of high-resolution US in the evaluation of peripheral nerve lesions.

© RSNA, 2003

Index Terms: Nervous system, neoplasms, 40.315, 40.325, 40.364 • Nervous system, US, 40.1298 • Neurofibromatosis, 40.1831 Neuroma, 40.315, 40.364


   Introduction
Top
 Abstract
 Introduction
Sonohistology
 Scanning Techniques
 Abnormalities
 Conclusion
 References
 
With the advent of state-of-the-art high-resolution ultrasound (US) scanners, normal peripheral nerves can be clearly demonstrated (1,2). In high-resolution US images, the nerve is seen as hypoechoic neuronal fascicles and echogenic surrounding connective tissue (3,4). Although most radiologists and clinicians prefer to use magnetic resonance (MR) imaging to evaluate the musculoskeletal system, including peripheral nerves, high-resolution US actually offers some advantages over MR imaging. High-resolution US is faster and more cost-effective, offers superior spatial resolution and a more dynamic study, and avoids the possibility of claustrophobia in patients. However, as with high-resolution US of the musculoskeletal system, high-resolution US of the peripheral nerves is operator dependent and requires a longer learning curve. The purpose of this review is to describe normal and commonly encountered pathologic findings at high-resolution US of the peripheral nerves.


   Sonohistology
Top
 Abstract
 Introduction
 Sonohistology
Scanning Techniques
 Abnormalities
 Conclusion
 References
 
The basic units of the peripheral nerve consist of a neural fiber embedded in endoneurium. Because the endoneurium is too thin to reflect the sound beam, it is hypoechogenic at high-resolution US. The neural fascicle consists of several neural fibers and is embedded in a capsule called perineurium. This capsule consists of connective tissue, vessels, and lymphatic ducts and is thick enough to reflect the sound beam, resulting in hyperechoic lines at high-resolution US. The trunk of the peripheral nerve consists of several neural fascicles and is embedded in a thicker membrane called epineurium, which is seen as bold echogenic lines at high-resolution US. Therefore, at high-resolution US the peripheral nerve is seen as several parallel echogenic lines within two bold echogenic lines in longitudinal sections and as a reticular pattern in transverse sections (Figs 1, 2).



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  		Figure 1.  Photograph (lower right) shows a short segment specimen of the median nerve. US scans show parallel echogenic lines (arrows) in the longitudinal section (Sag) and a reticular pattern (arrows) in the transverse section (Tr).

 


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  		Figure 2.  Photograph (middle) shows the location of the median nerve. US scans show parallel echogenic lines (arrows) in the longitudinal section (Sag) and a reticular pattern (arrows) in the transverse section (Tr).

 
The characteristics of this reticular pattern (ie, round hypoechoic areas surrounded by echogenic lines) make it easy to differentiate the nerve from surrounding hypoechoic muscles with the perpendicular sound beam. Because the nerve structure is similar to that of the tendon, it also has an apparently anisotropic effect that results in poor definition of the nerve in nonperpendicular sections. The echogenicity of the peripheral nerve is between the relatively low echogenicity of muscle and the higher echogenicity of tendon.


   Scanning Techniques
Top
 Abstract
 Introduction
 Sonohistology
 Scanning Techniques
Abnormalities
 Conclusion
 References
 
Before scanning, the surrounding anatomic structures, including bones, muscles, and vascular structure, must be recognized. The peripheral nerves that are most commonly examined in general practice are discussed here briefly.

The sciatic nerve is a large nerve bundle that can be traced from the popliteal fossa transversely, lateral to the popliteal vessels, between the biceps femoris (lateral) and the semimembranous and semitendinous (medial) muscle (Fig 3).



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  		Figure 3.  Photograph (right) shows the location of the sciatic nerve. US scan shows normal sciatic nerve (arrows) in the upper popliteal fossa region. BF = biceps femoris muscle, ST = semitendinosus muscle, SM = semimembranous muscle.

 
The common peroneal nerve normally separates from the posterior tibial nerve at the level of popliteal fossa, courses laterally and downward and crosses over the head of the fibula (Fig 4) (5).



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  		Figure 4.  Photograph (right) shows the location of the posterior tibial and peroneal nerves. US scan shows the normal posterior tibial nerve (arrows) and common peroneal nerve (arrowheads) in the popliteal fossa. BF = biceps femoris, ST = semitendinous muscle. A = popliteal artery.

 
The brachial plexus, which is just lateral and posterior to the anterior scalene muscle, is seen as several round hypoechoic neural trunks. The brachial plexus is formed by the anterior divisions of the spinal nerves of C5 to T1, with variable addition of C4, and roots, trunks, divisions, and cords from proximal to distal. The roots of the brachial plexus course between the anterior and middle scalene muscles adjacent to the subclavian artery (6,7). The scanning technique we used identifies the anterior scalene muscle within the transverse section. The roots are located behind the muscle (Fig 5).



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  		Figure 5.  Drawing (right) shows the normal brachial plexus in the neck region. Transverse US scan of the right side of the neck shows the C5-C8 nerve roots behind the anterior scalene muscle (AS). MS = middle scalene muscle, c = common carotid artery, v = vertebral artery.

 
The median nerve is traced in the palmar aspect of the wrist (Fig 6) and is located ventral to the flexor retinaculum, dorsal to the flexor digitorum tendons, and medial to the flexor carpi radialis tendon.



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  		Figure 6.  Drawing (bottom) shows the normal median nerve. US scans show the normal median nerve as parallel echoic lines (arrows) in the sagittal section (left) and as a reticular pattern (arrowheads) in the transverse section (right).

 
The median nerve can be traced from the wrist, between the flexor retinaculum and flexor digitorum tendons, to the forearm level, between the flexor digitorum superficial and profundus muscles, anterior to the brachial artery at midarm level, and crossing lateral to the brachial artery at the upper arm level (8). The median nerve enters the forearm from the cubital fossa, between the two heads of the pronator teres muscle, called the pronator teres tunnel.

The ulnar nerve can be traced from the posterior aspect of the medial epicondyle, both proximally and distally. The nerve is located between the flexor carpi ulnaris and flexor digitorum profundus muscles at the forearm level and is accompanied by the ulnar artery in the lower part of the forearm. Near the wrist level, the ulnar nerve runs lateral to the flexor carpi ulnaris tendon and crosses superficially to the flexor retinaculum tendon and lateral to the ulnar artery, which is also called the Guyon tunnel (8).

The radial nerve is easily traced from the spiral groove of the humeral bone proximally to an area between the medial and lateral heads of the triceps muscle (Fig 7), then distally to the lateral part of the cubital fossa, where it divides into superficial and deep branches.



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  		Figure 7.  Drawing (right) shows the normal radial nerve. Transverse US scan shows the normal radial nerve (arrows) in the spiral groove region. TRI = triceps muscle, H = humeral bone, BR = brachioradialis muscle.

 
We suggest using a high-frequency transducer for more detailed resolution. The frequency of the transducer should be more than 7.5 MHz in superficial locations and at least 5 MHz in deeper locations (eg, sciatic nerve), with a linear array to diminish distortion.


   Abnormalities
Top
 Abstract
 Introduction
 Sonohistology
 Scanning Techniques
 Abnormalities
Conclusion
 References
 
Causes of peripheral nerve lesions include trauma, inflammatory processes, compressive syndrome, neoplasms, and others.

Trauma
Most traumatic neuropathy is induced by iatrogenic or postoperative procedures (9-11). The mechanism of peripheral nerve injury might be due to dissection of the nerve, traction, insertion of retractors, heat, or release of a fibrotic band, which could result in random proliferation of axons, Schwann cells, and fibroblasts, mixed together to form a nonneoplastic mass (Figs 8, 9).



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  		Figure 8.  Traumatic neuroma. A 73-year-old woman underwent a forearm operation because of a median nerve schwannoma (open arrows, lower right image). One month later, she complained of persistent discomfort over the scar region, with a positive Tinel sign. Photograph (upper right) shows location of trauma. US scans (left images) show a hypoechoic structure with irregular margins (arrowheads) surrounding the median nerve (arrows), demonstrating scar tissue infiltration of the median nerve. Sag = sagittal, Tr = transverse.

 


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  		Figure 9.  Traumatic neuroma. A 48-year-old man underwent surgery after trauma to left forearm (location shown in photograph). Photograph (lower right) obtained 6 months later shows atrophy of left first web muscle (arrow). Transverse (Tr) US scans show enlarged ulnar nerve (arrowheads). Sagittal (Sag) scan shows enlarged distal ulnar nerve. U = ulnar artery.

 
The decision to treat surgically or conservatively is usually based on clinical examination and electrodiagnosis. The most severe condition due to peripheral nerve injury is the formation of traumatic neuroma, which results from a nonneoplastic proliferation of the proximal end of a completely or partially transected nerve (12) (Fig 10).



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  		Figure 10.  Traumatic neuroma. A 56-year-old man had traumatic injuries due to a car accident, including a large laceration over the left thigh that was treated with primary sutures only. Photograph (lower right) shows location of injury. One year later, he complained of a sharply painful sensation over the scar area, with a positive Tinel sign. US scans show a hypoechoic nodule with irregular margins (arrowheads) beside the femoral artery (A) and femoral nerve (arrows). Sag = sagittal, Tr = transverse.

 
The percutaneous brachial approach to carotid or vertebral angiography has been reported to be a safe and effective method (13) but may involve risk of injury to the median nerve. Delayed epineurial hematoma with secondary entrapment of the median nerve and secondary hemorrhage diathesis can occur in patients receiving anticoagulants (14,15) (Fig 11).



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  		Figure 11.  A 73-year-old man underwent brachial artery catheterization for cerebral angiography. The patient complained of a painful sensation over the elbow and right hand after the procedure. Photograph (middle) shows the location of injury. US scans of the elbow show an echo-free hematoma (arrowheads) in close contact with the median nerve (arrows) in the sagittal (Sag) view. In the transverse (Tr) view, the hematoma was found within the epineurium of the median nerve (arrows). Color Doppler image (lower left) shows the brachial artery beneath the hematoma.

 
US-guided aspiration of the perineural hematoma can be used to relieve pressure on the median nerve (15).

Inflammatory Processes
Inflammation of the neural bundle may be due to bacterial or viral infection or to autoimmune changes. Inflammatory or infectious change of perineural soft tissue might result in compression or invasion of the nerve. The cause of neuritis is usually unknown. High-resolution US of peripheral nerve neuritis might show normal morphology or diffuse swelling of the nerve with decreased echogenicity (Fig 12) (16,17).



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  		Figure 12.  Ulnar nerve neuritis. Photograph (bottom) shows location of the affected area. Transverse US scans of the ulnar nerve show swelling of the ulnar nerve (arrowheads) in the right arm (RT) compared with a normal ulnar nerve (arrows) in the left arm (LT) in a 35-year-old woman complaining of numbness of the fourth and fifth fingers of the right hand.

 
In patients with surrounding tissue infection, lymphadenitis, or abscess, high-resolution US will show the focal hypoechoic nodule with or without a thin echoic hilum (lymphadenitis) or heterogeneous hypoechoic abscess with invasion to the epineurium (Figs 13, 14).



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  		Figure 13.  Lower arm abscess. Photograph (middle) shows location of the affected area. Transverse US scans show an ill-defined hypoechoic abscess (thick arrows) compressing the ulnar (UN) (thin arrows) and median (MN) (thin arrows) nerves in a 41-year-old woman with painful swelling in the lower arm.

 


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  		Figure 14.  Median nerve compressed by lymphadenitis. Photograph (middle) shows location of the affected area. Transverse US scans show two enlarged lymph nodes (arrows) compressing the median nerve (arrowheads) in a 30-year-old man with carpal tunnel syndrome who complained of a painful sensation over the ventral aspect of the arm. A = brachial artery, V = brachial vein.

 
Compressive Syndromes
Compressive syndromes affecting the peripheral nerves include cubital tunnel syndrome, carpal tunnel syndrome, Guyon tunnel syndrome, tarsal tunnel syndrome, tumor compression, and nerve subluxation.

Cubital tunnel syndrome.—The cubital tunnel is a fibroosseous canal containing the ulnar nerve. A fascial band called the cubital tunnel retinaculum, which extends from the tip of the olecranon to the medial epicondyle, forms the roof of the tunnel (18—20). During the examination, the patient sits and faces the operator on the opposite side of the examination table and puts his or her arm on a pillow, dorsal side up. The transducer is placed perpendicularly on the posteromedial aspect of the elbow (Fig 15).



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  		Figure 15.  Photograph shows the scanning technique for the ulnar nerve.

 
The scanning technique focuses on the ulnar nerve and measures the short and long axes of the nerve at a level 5 cm above and below the medial epicondyle (21). At the level of the epicondyle, cubital tunnel syndrome is considered if the area of ulnar nerve is larger than 0.075 cm2 or the shortest diameter is longer than 0.19 cm (Figs 16–21).



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  		Figure 16.  Normal ulnar nerve. Photograph (right) shows the area scanned. A 60-year-old man volunteered to undergo a US examination during a routine physical health check-up. Transverse US scan of his right dorsal medial arm at a level 5 cm above the medial epicondyle shows a round-to-ovoid hypoechoic ulnar nerve with a reticular pattern (arrows). T = medial head of triceps muscle, B = biceps muscle.

 


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  		Figure 17.  Normal ulnar nerve (epicondyle level) in the same volunteer as in Figure 16. Photograph (right) shows the area scanned. Transverse US scan at the right medial epicondyle level shows a 0.13 x 0.51 cm ovoid hypoechoic ulnar nerve (arrows). E = medial epicondyle.

 


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  		Figure 18.  Normal ulnar nerve (forearm level) in the same volunteer as in Figure 16. Photograph (right) shows the area scanned. Transverse US scan of the right medial forearm at a level 5 cm below distal to the medial epicondyle shows an ovoid heterogeneously echoic ulnar nerve (arrows) with a reticular pattern, lying between the flexor carpi ulnaris (C) and the flexor digitorum profundus (D) muscles.

 


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  		Figure 19.  Cubital tunnel syndrome. Photograph (right) shows the area scanned. Transverse US scan of the right elbow (RT) shows swelling of the ulnar nerve (arrowheads) at the medial epicondyle level, compared with the normal left arm (LT) (arrows). This 55-year-old woman complained of numbness of the fourth and fifth fingers of the right hand. Cubital tunnel syndrome was diagnosed by means of nerve conduction velocities and electromyography.

 


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  		Figure 20.  Cubital tunnel syndrome. Transverse US scan in a 45-year-old woman shows swelling of the ulnar nerve (arrows) in the left arm (LT) at the medial epicondyle level, compared with a normal ulnar nerve (arrows) in the right arm (RT).

 


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  		Figure 21.  Cubital tunnel syndrome: ganglion. Photograph (lower right) shows the area scanned. US scans show a hypoechoic ganglion (arrowheads) compressed to the ulnar nerve (arrows) in the transverse (Tr) and sagittal (Sag) views in a 50-year-old man. Color Doppler US shows no vascularity in the ganglion.

 
Ulnar nerve dislocation.—Dislocation of ulnar nerve has been reported in some healthy persons. Abnormal ulnar nerve location over the medial epicondyle might result in nerve injury (22). The dislocation of ulnar nerve results from abnormal movement of the ulnar nerve out of the cubital tunnel and over the medial epicondyle during elbow flexion (22). Dynamic sonography of the elbow can depict this dislocation (Fig 22).



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  		Figure 22.  Ulnar nerve dislocation. Photographs (bottom) show the area scanned in extension and flexion. Transverse US scans of the elbow in extension and flexion in a 25-year-old man complaining of occasional numbness of the fourth and fifth fingers show an unusual location of the ulnar nerve (arrowheads), lateral to the medial epicondyle in extension but medial to the medial epicondyle during flexion E = medial epicondyle.

 
The patient's position and the scanning technique are the same as those used to assess cubital tunnel syndrome, including flexion and slow elbow extension.

Guyon tunnel syndrome.—The ulnar nerve and artery pass through the Guyon tunnel, located between the pisiform bone medially and the hamate bone laterally at the wrist (23). The most frequent causes of Guyon tunnel syndrome are ganglion (Fig 23), trauma (24), and, rarely, tenosynovitis or neoplasms (Fig 24).



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  		Figure 23.  Guyon tunnel syndrome: ganglion. Photograph (bottom) shows the area scanned. A 30-year-old woman complained of a palpable nodule in the ulnar aspect of the wrist, with numbness of the fifth finger. Transverse US scans of the wrist show an anechoic ganglion (G) compressing the ulnar nerve (arrowheads) at wrist level. The ulnar nerve is located between the ulnar artery and ganglion.

 


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  		Figure 24.  Guyon tunnel syndrome. Photograph (bottom right) shows the area scanned. Transverse (left) and sagittal (top right) US scans show a well-defined hypoechoic nodule (arrowheads) in the wrist, compressing the ulnar nerve (arrows) in a 48-year-old man in whom leiomyoma was diagnosed. Color Doppler image (bottom left) shows the ulnar nerve (A) located between the tumor and ulnar artery.

 
Pronator syndrome—This is an entrapment neuropathy of the median nerve in the antecubital region, where the nerve passes between the two heads of the pronator teres muscle and then under the flexor digitorum sublimis muscle (25). Causes of pronator syndrome include muscle hypertrophy, fibrotic change, and ganglion. (Fig 25)



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  		Figure 25.  Pronator syndrome. Photograph (bottom right) shows the area scanned. Sagittal (top left) and transverse (bottom left) US scans show a small anechoic ganglion (arrowheads) compressing the median nerve (arrows) in a 33-year-old woman with numbness of the right palm during compression of the anterior cubital fossa. Compare the right arm (RT) and the normal left arm (LT) (toop right) pronator tunnel regions. Large A = brachial artery. Small A and B are measurements of the size of the median nerve.

 
Carpal tunnel syndrome.—This syndrome is produced by compression of the median nerve at the wrist, resulting in numbness, tingling, and pain in the hand. Electrodiagnostic testing is important for the accurate diagnosis of carpal tunnel syndrome (26). US criteria for median nerve compression include the classic triad: nerve flattening in the distal tunnel, nerve swelling in the distal radius region, and palmar bowing of the flexor retinaculum (Fig 26) (27,28).



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  		Figure 26.  Carpal tunnel syndrome. Photograph (bottom right) shows the area scanned. Sagittal US scans show swelling of the proximal portion of the median nerve (arrows) in the right wrist (RT) in a 45-year-old woman. Color Doppler US shows increased vascularity in the swollen part of the nerve. Compare with the normal median nerve (arrowheads) in the left wrist (LT).

 
High-resolution US is a simple and noninvasive modality, and it should be considered as an initial evaluation method for carpal tunnel syndrome. If the US findings are negative in patients with positive clinical findings, electromyography and nerve conduction velocity measurements are then used for further evaluation (28,29). If the nerve is compressed by extrinsic factors, US is a suitable diagnostic modality (Figs 27, 28) (28,30–32).



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  		Figure 27.  Carpal tunnel syndrome: ganglion. Photograph (right) shows the area scanned. Transverse US scan of median nerve at wrist level shows a hypoechoic ganglion (arrows) compressing the median nerve (arrowheads) in a 30-year-old woman who complained of numbness of the left hand.

 


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  		Figure 28.  Palm ganglion with median nerve compression. Photograph (right) shows the area scanned. Transverse US scan of the median nerve at wrist level shows an anechoic ganglion (arrows) compressing the median nerve (arrowheads) in a 60-year-old man.

 
Tarsal tunnel syndrome.—The tarsal tunnel is located ventral to the flexor retinaculum at the level of the medial malleolus region. Along with the posterior tibial nerve and vessels, the tibialis posterior, flexor digitorum longus, and flexor hallucis longus tendons pass through this tunnel. Compression of the posterior tibial nerve at this level results in tarsal tunnel syndrome (33). The causes of tarsal tunnel syndrome include trauma, synovial inflammation, neoplasms (eg, ganglion, neuroma), and vascular deformity. High-resolution US can show the posterior tibial nerve to the divisions of the medial and lateral plantar nerves. The extrinsic causes of tarsal tunnel syndrome, such as ganglion, neurogenic tumor, and tenosynovitis, can be diagnosed with high-resolution US (Figs 29, 30).



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  		Figure 29.  Tarsal tunnel syndrome: ganglion. Photograph (bottom) shows the area scanned. A 28-year-old woman complained of a painful sensation with radiation to the foot during compression of the medial aspect of the right ankle. US of the medial malleolus in transverse (Tr) and sagittal (Sag) views shows an anechoic ganglion (arrowheads) with compression of the posterior tibial nerve (arrows). A = posterior tibial artery.

 


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  		Figure 30.  Tarsal tunnel syndrome: ganglion. Photograph (bottom) shows the area scanned. A 38-year-old woman complained of a palpable nodule over the medial aspect of the left ankle. US in transverse (Tr) and sagittal (Sag) views shows an anechoic ganglion (G) with compression of the posterior tibial nerve (arrowheads).

 
Tumor compression.—After entrapment in osteofibrous tunnels, the next most frequent cause of nerve compression is ganglion. More rare causes are fibrotic scar and benign or malignant tumors (Figs 31, 32).



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  		Figure 31.  Ulnar nerve compressed by hemangioma. Photograph (bottom) shows the area scanned. Transverse (Tr) US scan shows intramuscular hemangioma (arrows) with compression of the ulnar nerve (arrowheads) in a 32-year-old woman complaining of a palpable soft mass in the dorsal aspect of the arm. Sagittal (Sag) color Doppler scan shows hypervascularity in the hemangioma (arrows).

 


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  		Figure 32.  Ulnar nerve compressed by tumor. Photograph (bottom) shows the area scanned. A 50-year-old man had cubital tunnel syndrome caused by tumor (arrowheads) compression of the ulnar nerve (arrows). Sagittal (Sag) US and color Doppler scans show hypervascularity in the tumor, which was identified as a sarcomatous metastasis.

 
The typical sonographic pattern of ganglion is a well-defined margin and echo-free cystic structure, sometimes with septations (Fig 33).



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  		Figure 33.  Radial nerve compression by ganglion. Photograph (bottom) shows the area scanned. US scans in transverse (Tr) and sagittal (Sag) views show an anechoic ganglion (G) compressing the radial nerve (arrowheads) in a 45-year-old woman complaining of a palpable nodule in the anterior cubital fossa, with a positive Tinel sign.

 
Fibrotic scarring usually occurs after trauma. The compressed nerve will swell proximal to the region of the scar (Fig 34).



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  		Figure 34.  Compression of the common peroneal nerve. An 18-year-old man complained of numbness in the lateral aspect of the left lower leg after primary suture for injuries sustained in a car accident. Sagittal US scan shows focal swelling of the common peroneal nerve (arrows). The patient underwent surgery (photograph), during which fibrotic band compression of the common peroneal nerve, resulting in proximal edema (arrows), was found.

 
Neoplasms and Other Lesions
Peripheral nerve tumors of extremities are uncommon. The reported prevalence of hand and arm peripheral nerve tumors varies from 1% to 4.9% of all upper-extremity tumors (34,35). The most common tumors of peripheral nerves are neurofibromas and schwannomas. Other benign and malignant peripheral nerve sheath tumors, such as neurofibromatosis (Fig 35), glomus (Fig 36), fibromatosis infiltration of the nerve (Fig 37), and sarcoma invasion or metastasis (Figs 38, 39), are rare.



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  		Figure 35.  Neurofibromatosis: diffuse type. Photograph (right) shows the discolored skin regions in an 8-year-old girl and the areas scanned. US scan of the discolored skin region (top left) shows infiltrative hypoechoic nodules (arrowheads) within the dermis to the subcutaneous layer. Compare with the scans of the normal skin region (middle). Color Doppler scan (bottom left) shows increased vascularity within the tumor.

 


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  		Figure 36.  Glomus tumor. Photograph (right) shows the area scanned. A 47-year-old woman complained of sharp pain during compression and a temperature change in her right index fingertip. Sagittal (Sag) US scan shows a well-defined hypoechoic nodule (G) with bone erosion (arrows). Color Doppler scan shows hypervascularity in the nodule. A glomus tumor was identified.

 


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  		Figure 37.  Ulnar nerve encased by fibromatosis. Photograph (bottom) shows the area scanned. A 22-year-old woman complained of a painful nodule in the hypothenar region of the palm. US scans in transverse (Tr) and sagittal (Sag) views show a lobulated hypoechoic nodule (arrows) encasing the ulnar nerve (arrowheads). The nodule proved to be fibromatosis.

 


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  		Figure 38.  Sarcoma invasion of the posterior tibial nerve. Photograph (bottom right) shows the area scanned. A 57-year-old woman complained of a painful mass in the popliteal fossa. US scans in transverse (Tr) and sagittal (Sag) views show an ill-defined hypoechoic mass (arrows) with invasion of the posterior tibial nerve (arrowheads). The mass was identified as high-grade sarcoma.

 


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  		Figure 39.  Radial nerve compressed by metastasis. Drawing (middle) shows the area scanned. A 70-year-old woman complained of a painful mass in the right arm. US scans in transverse (Tr) and sagittal (Sag) views show humeral bone destruction, with a surrounding soft-tissue mass (T) compressing the radial nerve (arrowheads). Hypervascularity within the tumor is noted on the color Doppler scan. Metastatic carcinoma was diagnosed.

 
Most peripheral neurogenic tumors are ovoid with well-defined margins, heterogeneously hypoechoic with cystic and solid components in the soft-tissue mass at high-resolution US, and hypervascular at color Doppler US (36). Neurogenic tumors do not always originate from a large neural trunk; however, if the tumor originates from a major trunk of peripheral nerve or is in close contact with the neural trunk, the possibility of neurogenic tumor becomes high. It is, however, difficult to differentiate schwannoma from neurofibroma with high-resolution US alone (Figs 40–47).



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  		Figure 40.  Schwannoma. Photograph (bottom) shows the area scanned. US scans show a lobulated mass (arrows) along the posterior tibial nerve in a 48-year-old woman complaining of a painful mass in the calf, identified as schwannoma.

 


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  		Figure 41.  Radial nerve schwannoma. Photograph (right) shows the area scanned. US scans show a heterogeneously hypoechoic nodule (arrows) with cystic and solid components along the radial nerve (arrowheads) in a 86-year-old man complaining of a painful nodule in the arm, identified as schwannoma.

 


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  		Figure 42.  Common peroneal nerve schwannoma. Photograph (bottom right) shows the area scanned. A 30-year-old woman complained of a painful nodule in the lateral popliteal region. Sagittal US scan shows a hypoechoic nodule (arrows) along the common peroneal nerve (arrowheads). Color Doppler scan shows a hypervascular tumor.

 


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  		Figure 43.  Hand schwannoma. Photograph (right) shows the area scanned. A 27-year-old woman complained of painful nodules in the third finger. US scans in transverse (Tr) and sagittal (Sag) views show a lobulated hypoechoic lesion (arrows) within the digital nerve. Compare with the transverse view of the fourth finger (4th) with a normal digital nerve (arrowheads). t = flexor tendon.

 


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  		Figure 44.  Posterior tibial nerve neurofibroma. Photograph (bottom) shows the area scanned. Sagittal US scans show a heterogeneously echoic nodule with a target pattern and well-defined margin (arrowheads) in the posterior tibial nerve (arrows) in a 55-year-old woman complaining of a painful nodule in the left calf. Color Doppler scan shows hypervascular tumor, later identified as a neurofibroma.

 


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  		Figure 45.  Medial tarsal nerve neurofibroma. Photograph (middle) shows the area scanned. US scan shows a hypoechoic nodule (arrowheads) with a well-defined margin in close contact with the medial tarsal nerve (arrows) in a 38-year-old man complaining of foot pain and with a positive Tinel sign in the medial aspect of the foot. Hypervascularity in the tumor, identified as neurofibroma, is noted on the color Doppler scan.

 


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  		Figure 46.  Median nerve neurofibroma. Photograph (middle) shows the area scanned. A 45-year-old man complained of a painful nodule in the palmar aspect of the forearm. US scans in transverse (Tr) and sagittal (Sag) views show a well-defined hypoechoic nodule (arrows) in close contact with the median nerve (arrowheads). Color Doppler scan shows hypervascularity within the tumor, which was identified as a neurofibroma.

 


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  		Figure 47.  Neurofibroma. Photograph (middle) shows the area scanned. A 71-year-old man complained of a painful mass in the medial aspect of his right thigh. US scans show a well-defined hypoechoic mass (arrowheads) with cystic and solid component in the medial thigh. Color Doppler scan shows hypervascularity within the tumor, which was identified as a neurofibroma.

 
Neurofibromatosis, also known as von Recklinghausen disease, is a phakomatosis that has a wide spectrum of clinical expression, with involvement of neurocutaneous and multiple organ systems (37). Neurofibromatosis can be divided into two major forms: neurofibromatosis type 1 (NF1) and type 2 (NF2). NF1 commonly involves the peripheral nerves, whereas NF2 mainly affects the central nervous system. The NF1 neurofibromas can be divided into three types: localized, plexiform, and diffuse (38,39). The localized type is similar to the solitary neurofibroma. The plexiform type usually involves a long segment of a major nerve trunk and has been described as "strings of peanuts" (Fig 48). The diffuse type is typically localized in the subcutaneous layer (Fig 35).



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  		Figure 48.  Congenital neurofibromatosis (plexiform type). Photograph and drawings show the areas scanned. A 71-year-old man complained of multiple palpable nodules in all four limbs. US scans show several well-defined hypoechoic nodules along the tracts of peripheral nerves (median [MN}, radial [RN], and ulnar [UN]) in the arm. Color Doppler scan shows that the tumor has poor vascularity. High-resolution US of the diffuse type of NF1 usually shows diffuse, tiny hypoechoic nodules infiltrating the subcutaneous and dermis layers (Fig 35).

 
Glomus bodies consist of an afferent arteriole, a tortuous arteriovenous anastomosis, a system of collecting veins, and a neurovascular reticulum that regulates the flow of blood through the anastomosis. They are present in the stratum reticularis of the dermis throughout the body but are more prevalent in the digits. Wood described the glomus tumor as a painful subcutaneous "tubercle" (40). It is usually located in the subungual region and presents as a small homogeneous hypoechoic nodule at high-resolution US and shows hypervascularity at color Doppler US (Fig 36).


   Conclusion
Top
 Abstract
 Introduction
 Sonohistology
 Scanning Techniques
 Abnormalities
 Conclusion
References
 
The limitations of the application of high-resolution US to the evaluation of the musculoskeletal system, including the peripheral nerves, are its operator dependence and its relatively long learning curve. However, this modality can be adequate and cost-effective for the evaluation of the peripheral nerves and surrounding lesions. At high-resolution US, the normal peripheral nerve is usually seen in a parallel (sagittal view) or reticular (transverse view) pattern and is surrounded by muscles, tendons, ligaments, vessels, and bones. Careful examination with an accurate scanning technique and good knowledge of the anatomic relationships of nerves to surrounding structures might provide the correct information to the clinician for selecting the appropriate treatment. High-resolution US is an effective imaging modality for capturing morphologic changes in the peripheral nerves and for making correct diagnoses. It could be used either as a first-line imaging modality in patients with suspected peripheral nerve lesions before further treatment is administered or as a useful tool for follow-up imaging.


   References
Top
 Abstract
 Introduction
 Sonohistology
 Scanning Techniques
 Abnormalities
 Conclusion
 References
 

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