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n 1988, Fornage [1] produced thefirst review of imaging findings ofperipheral nerves using sonogra-

phy. Continual technologic improvements, in-cluding the availability of high-frequencytransducers (6-13–MHz) and variable footprintsizes, have led to an increase in the use ofsonography in the imaging of peripheralnerves [2–4]. We believe that sonographyshould be the primary technique for imaging

peripheral nerve pathology because it is inex-pensive and widely available, has no contrain-dications, and allows rapid, detailed imagingof the entire length of the major peripheralnerves of both limbs.

In our practice, we routinely use a 5-12–MHz linear array transducer (HDI 5000,ATL, Bothell, WA) to scan the entire periph-eral nerve in both transverse and longitudinalplanes. Normal peripheral nerves have a typi-

cal sonographic appearance, showing multi-ple longitudinal hypoechoic bands, whichrepresent fascicular bundles. These are sepa-rated by discontinuous bands of increasedechogenicity, corresponding to the sur-rounding epineurium [1, 3] (Fig. 1A). Inthis article, we describe the sonographicappearances of normal peripheral nervesand important examples of peripheralnerve disorders.

Sonography of Peripheral Nerve Pathology

R. M. Stuart

1

, E. S. C. Koh

1

, W. H. Breidahl

1,2

Received July 15, 2002; accepted after revision May 14, 2003.

1

Department of Diagnostic and Interventional Radiology, Royal Perth Hospital, GPO Box X2213, Wellington St., Perth 6847, Western Australia.

2

Perth Radiological Clinic, 127 Hamersley Rd., Subiaco, Perth 6008, Western Australia. Address correspondence to W. H. Breidahl ([email protected]).

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2004;182:123–129 0361–803X/04/1821–123 © American Roentgen Ray Society

Pictorial Essay

I

A B

C

Fig. 1.—31-year-old man with normal median nerve.A, Photomicrograph of histologic section of normal median nerve shows multiple nerve fibers(axons) with accompanying Schwann cells. Myelin sheaths are bound together by thin col-lagen strands called endoneurium. This group of fibers represents a single fascicle, which isensheathed by further dense connective tissue, perineurium (arrow). Epineurium (E) is thickouter interdigitating connective tissue, which surrounds multiple fascicles to form peripheralnerve. Histologic correlation has shown that number of hypoechoic bands seen at sonogra-phy does not correlate exactly with number of fascicles [2].B, Longitudinal 5-12–MHz sonogram shows multiple longitudinal hypoechoic bands, repre-senting fascicular bundles (arrows). Note hyperechoic discontinuous bands separating bun-dles that correspond to surrounding intervening epineurium.C, Transverse 5-12–MHz sonogram of normal median nerve shows discrete hypoechoic fas-cicular bundles (arrows) seen end-on.

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Fig. 3.—41-year-old man with traumatic neuroma.Longitudinal 5-12–MHz sonogram shows localizedswelling of tibial nerve (arrowheads) at site of iatro-genic injury.

A B

Fig. 4.—30-year-old man with pain after forearm amputation for undifferentiated sarcoma.A, Compound transverse 5-12–MHz sonogram of proximal forearm shows three enlarged, well-defined, ovoid hypoechoic masses at amputated ends of ulnar (thin blackarrow), median (thick black arrow), and superficial branch of radial (white arrow) nerves.B, Longitudinal 5-12–MHz image of central-most of three hypoechoic masses shows median nerve (straight arrow) extending to neuroma (curved arrow). Follow-up imag-ing (not shown) at 6 months revealed no change.

A B

Fig. 2.—13-year-old girl with neural fibrolipoma of median nerve.A, Transverse 5-12–MHz sonogram shows enlarged hypoechoic fascicles separated by extensive echogenic (fatty) infiltrate (arrows). B, Axial T1-weighted image (TR/TE, 500/14) shows cablelike thick hypointense bands separated by abundant fatty tissue, all of which are diagnostic of neural fibrolipoma.

Sonography of Peripheral Nerve


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Focal Intrinsic Neural Lesions

Neural Fibrolipoma

Neural fibrolipoma is a disorder of un-known origin that causes infiltration of theperineurium and epineurium with fibrofattytissue. More than 80% of cases involve themedian nerve, although the brachial plexus,ulnar, radial, and peroneal nerves may alsobe affected. When neural fibrolipoma is asso-ciated with unilateral macrodactyly, it istermed “macrodystrophia lipomatosa” andtends to affect the second or third digit of thehand or foot. There is extensive fatty infiltra-tion of the nerve and the whole digit, withaccompanying osseous overgrowth. Sonog-raphy shows thickened alternating hypere-choic and hypoechoic bands, reflecting thefibrofatty infiltrate [2, 3] (Fig. 2).

Traumatic Neuroma

Traumatic neuromas are proliferativemasses that represent a disorganized attemptat nerve regeneration. They are often clini-cally palpable as small, firm, tender masses.Spindle neuromas are a focal fusiform massoccurring in intact nerves caused by chronicirritation. Terminal (amputation) neuromasresult from partial or complete transection ofthe nerve and arise at the proximal nerveend. The most common site of occurrence isin the lower limbs after surgical amputation.Because of their fibrous capsule, traumaticneuromas are usually well defined and hypo-echoic with attenuation characteristics simi-lar to muscle [1, 3] (Figs. 3 and 4).

Morton’s Neuroma

The term “Morton’s neuroma” is a misno-mer that describes a benign mass of perineu-ral fibrosis involving a plantar digital nervelying between two metatarsal heads. Mor-ton’s neuromas may be multiple and bilateraland most commonly occur between theheads of the third and fourth metatarsals;they are likely to develop because of frictionof the nerve against the transverse intermeta-tarsal ligament. On sonography, an ovoid hy-poechoic compressible mass is visible in theintermetatarsal space [2, 3] (Fig. 5). Fluidwithin the intermetatarsal bursae is a com-mon associated finding affecting the firstthree web spaces that may also be seen onsonography [5].

Intraneural Perineuroma

Intraneural perineuroma is a rare focalneural lesion that causes a slowly progres-sive painless mononeuropathy. Histologic andcytogenetic analyses reveal onion bulb–shapedwhorls of neoplastic perineural cell proliferation.The region of the peripheral nerve abnormalitycan be determined using electromyography andnerve conduction studies [6]. Sonographyshows the lesion to be hypoechoic, with mildlyelongated fusiform enlargement of the involvednerve (Fig. 6).

Peripheral Nerve Sheath Tumors

The benign peripheral nerve sheath tu-mors that are most commonly described are

Fig. 5.—24-year-old woman with surgically excised Morton’s neuroma. Preoperative longitudinal 5–12 MHzsonogram shows discrete oval hypoechoic mass (open arrows), lying between metatarsal heads. Digital nerve(solid arrow) can be seen proximal to mass.

A B

Fig. 6.—34-year-old man with intraneural perineuroma diagnosed after surgical biopsy. A, Longitudinal 5-12–MHz sonogram shows fusiform hypoechoic swelling of right common peroneal nerve (arrows).B, Axial STIR MRI shows intraneural perineuroma of common peroneal nerve at level of proximal popliteal fossa, with enlarged hyperintense fasciculi (open arrow)between biceps femoris muscle (B) and lateral head of gastrocnemius muscle (G). Compare with healthy tibial nerve (solid arrow) between veins.

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the schwannoma and the neurofibroma.Schwannomas are encapsulated tumors thatgrow eccentrically along the nerve axis,within the epineurium, thus often allowingthe tumor to be surgically excised withoutloss of neurologic function. Neurofibromas

most commonly arise sporadically, either ina diffuse cutaneous form or as a solitary pe-ripheral nerve tumor. The plexiform neurofi-broma is a rarer neoplasm that typicallyinfiltrates the fascicular bundles of largenerve trunks and is virtually pathognomonic

of neurofibromatosis 1. These tumors aresurgically inseparable from the host nerveand can undergo malignant transformation[1–3].

Sonography is unreliable in distinguishingbetween schwannomas and neurofibromas;

Fig. 7.—32-year-old man with schwannoma. Longitudinal composite 5-12–MHzsonogram of ulna nerve in upper arm shows elongated hypoechoic mass withhealthy nerve entering and exiting tumor (arrows). Diagnosis was confirmed atopen biopsy.

Fig. 8.—38-year-old man with schwannoma. Longitudinal 5-12–MHzsonogram shows cystic degeneration as anechoic spaces in schw-annoma of radial nerve, biopsied under sonography guidance.

A B

Fig. 9.—43-year-old man with ulnar neuritis. A, Transverse 5-12–MHz sonogram shows hypoechoic enlarge-ment of right ulnar nerve (arrow) in cubital tunnel.B, Sonogram obtained at same magnification shows normal cal-ibre of contralateral left ulnar nerve (arrow) for comparison withA. Symptom relief followed ulnar nerve decompression.

A B

Fig. 10.—31-year-old male busdriver with pronator teres syn-drome.A, Transverse 5-12–MHz sono-gram shows aberrant path ofright median nerve (straight ar-rows) through humeral head ofpronator teres with deep fas-cia inferiorly (curved arrow).B, Sonogram shows normal leftmedian nerve at same level(straight arrows) passes beneathhumeral head of left pronatorteres with deep fascia againshown (curved arrow). Recentchange to driving new bus cor-responded to onset of symptomsthat resolved on return to drivingold bus.



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both appear as discrete homogeneous ovoidhypoechoic masses, with a healthy nerve atthe proximal and distal aspects of the mass(Fig. 7). The presence of cystic degenerationfavors schwannoma rather than neurofi-broma [1–3] (Fig. 8).

Malignant peripheral nerve sheath tumorsarise from the transformation of a plexiformneurofibroma in neurofibromatosis 1 in 50%of cases, although previous radiotherapy caninduce the development of these rare andhighly malignant tumors. On sonography,they appear as hypoechoic lesions, oftenwith indistinct margins [3].

Nerve Entrapment

As peripheral nerves pass through fi-broosseous tunnels, they are vulnerable tocompression from a variety of extrinsiccauses: congenital, traumatic, synovitis, in-filtration, ganglia, tumor, and other acquireddisorders. Neural compression leads to is-chemia and venous congestion. If chronic,this may cause fibrosis and loss of nervefunction with atrophy of the innervated mus-culature. Clinical manifestations and nerveconduction studies generally give the diag-nosis. However, in atypical cases, sonogra-phy can show causative extrinsic

abnormalities at the site of compression,with associated changes in nerve contour andechotexture [2, 4, 7]. The peripheral nervesthat sonography can evaluate in entrapmentsyndromes include the suprascapular, me-dian, ulnar, radial, sciatic, tibial, and com-mon peroneal nerves (Figs. 9–11).

Nerve Dislocation

As it courses behind the posterior aspectof the elbow, the ulnar nerve normally lies inthe cubital tunnel. During elbow flexion,sonography can be used to scan dynamically,showing ulnar nerve dislocation; the nerve

Fig. 11.—39-year-old man with carpal tunnel syn-drome. Longitudinal 5-12–MHz sonogram showsechogenic oval mass (arrows) found to be tendonsheath fibrolipoma within carpal tunnel at surgery.

A

B

Fig. 12.—34-year-old man with ulnarnerve dislocation.A, Transverse 5-12–MHz sonogramof cubital tunnel using small foot-print probe shows ulnar nerve (openarrow) lying in normal positionwithin sulcus, lateral to medial epi-condyle (solid arrow) when elbow isextended. B, Transverse 5-12–MHz sonogramobtained with elbow flexion showsthat ulnar nerve (curved arrow) dis-locates anteromedially out of sulcus(straight arrow).

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A B C

Fig. 13.—47-year-old woman with longstanding brachial neuritis (Parsonage-Turner syndrome).A, Longitudinal 5-12–MHz sonogram shows increased echogenicity within atrophic right infraspinatus muscle (arrows), caused by denervation. B, Sonogram shows normal echogenicity on contralateral side at same magnification (arrows). C, Sagittal oblique T1-weighted image (TR/TE, 500/14) of same shoulder as in B shows atrophy and fatty infiltration of infraspinatus (I) as well as supraspinatus (S)muscles. Subscapularis (SU) muscle bulk is normal.

A B

C

Fig. 14.—60-year-old man with right calf pseudohy-pertrophy. A, Longitudinal 5-12–MHz sonogram shows increasedechogenicity within gastrocnemius (arrows) and so-leus muscles of right calf. Increased muscularechogenicity and bulk, caused by fatty infiltration,confirms pseudohypertrophy on sonography. B, Longitudinal 5-12–MHz sonogram shows normalleft gastrocnemius (G) and soleus (S) muscles forcomparison.C, Axial T1-weighted image (TR/TE, 500/14) shows en-largement and fatty replacement within right soleus(S) and gastrocnemius (MG) muscles, compared withhealthy left side.



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becomes displaced around and anterior to thetip of the medial epicondyle on flexion of theelbow (Fig. 12). Sonography can also differ-entiate ulnar nerve dislocation from othercauses of medial elbow pain and ulnar nerveneuropathy, such as cubital tunnel syndromeand snapping triceps syndrome

[8].

Muscle Changes Resulting from Nerve Pathology

Denervating neuromuscular disorders typ-ically result in soft-tissue and muscle atro-phy; this is associated with loss of musclebulk and fatty infiltration. Causes includeacute brachial neuritis and quadrilateralspace syndrome. Pseudohypertrophy repre-sents a combination of true muscle hypertro-phy and an increase in intramuscularconnective tissue and fat. Pseudohypertrophyfrequently occurs in the calf muscles, andthis phenomenon is seen in some dystrophicmuscle conditions, hemihypertrophy syn-dromes, and chronic neuropathies. True mus-

cle hypertrophy results from a pure increasein muscle bulk, without fatty infiltration.This is a paradoxical response to nerve injuryand, although rare, it is associated withchronic nerve irritation [9] (Figs. 13–15).

Acknowledgment

We thank Barbara Taylor, Radiology Li-brarian, Royal Perth Hospital, for her assis-tance in manuscript preparation.

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A B

Fig. 15.—35-year-old man with true hypertrophy.A, Transverse 5-12–MHz sonogram of right calf shows enlargement of tibialisanterior muscle (arrows), caused by chronic stimulation of deep peronealnerve. Normal echogenicity is maintained in hypertrophic muscle.B, Sonogram shows healthy left calf (arrows) at same magnification as A forcomparison.

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