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Peripheral Nerve Ultrasound

Jon A. Jacobson, M.D.

Professor of Radiology

Director, Division of Musculoskeletal Radiology

University of Michigan

Normal Peripheral Nerve

• Ultrasound appearance:– Hypoechoic nerve

fascicles– Hyperechoic connective

tissue• Transverse:

– Honeycomb appearance

Silvestri et al. Radiology 1995; 197:291 Median Nerve

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Volar Wrist: median nerve

Sagittal T1w Longitudinal

RadiusRadius LunateLunate

CapitateCapitate

F

Nerve Entrapment

• US findings:– Nerve enlargement proximal to entrapment

• Best appreciated transverse to nerve

– Abnormally hypoechoic• Especially the connective tissue layers

– Variable enlargement or flattening at entrapment site

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Common Peroneal Nerve: entrapment

Extensor Musculature (Short Axis)

Asymptomatic Atrophy

Nerve Entrapment Syndromes

• Median: – Carpal tunnel syndrome

– Pronator teres syndrome

• Ulnar:– Ulnar tunnel syndrome

– Cubital tunnel syndrome

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Volar Wrist

From: Netter’s Atlas of Human Anatomy

Carpal Tunnel Syndrome:

• Proximal median nerve swelling– Area: circumferential trace– Normal: <9 mm2

– Borderline: 9 – 12 mm2

– Abnormal: > 12 mm2

• 12.8 mm2 = moderate (83% sens, 95% spec)

• 14.0 mm2 = severe (77% sens, 100% spec)

Klauser AS et al. Sem Musculoskel Rad 2010; 14:487Ooi et al. Skeletal Radiol 2014; 43:1387

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Carpal Tunnel Syndrome

• Compare areas:– Proximal: pronator quadratus

– Distal: carpal tunnel

• ≥ 2 mm2 = carpal tunnel syndrome

• 99% sensitivity

• 100% specificity

Klauser AS. Radiology 2009; 250:171

PQ Rad

21 mm2

9 mm2

Bifid Median Nerve + CTS

Short Axis

• Carpal tunnel syndrome

• Change in cross-sectional area of ≥ 4 mm2

• Proximal: pronator quadratus

• Distal: at carpal tunnel

Klauser et al. Radiology 2011; 259; 808

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Nerve Entrapment Syndromes

• Median:– Carpal tunnel syndrome

– Pronator teres syndrome

• Ulnar:– Ulnar tunnel syndrome

– Cubital tunnel syndrome

Guyon’s canal: normal

Axial T1w Transverse

UlnarArtery

Pisiform

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Guyon’s Canal:• Ulnar tunnel syndrome

– Ulnar nerve compression – Accessory Abductor Digiti Minimi1

• Variant: up to 24% of wrists• Hypothenar hammer syndrome2

– Trauma– Ulnar artery thrombosis + distal emboli

1AJR 1999; 172:13972J Vasc Surg 1987; 5:838

Accessory Abductor Digiti Minimi Muscle

Transverse Longitudinal

Ulnar Nerve

Ulnar NerveP

a

Courtesy of V. Flores, MD, Texas

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Nerve Entrapment Syndromes

• Median: – Carpal tunnel syndrome

– Pronator teres syndrome

• Ulnar:– Ulnar tunnel syndrome

– Cubital tunnel syndrome

Ulnar Nerve: anatomy• Behind medial epicondyle

of humerus:– Cubital tunnel retinaculum or

Osborne fascia• Distal to epicondyle:

– True cubital tunnel– Between ulnar and humeral

heads: flexor carpi ulnaris– Under arcuate ligament

Martinoli, C. et al. Radiographics 2000;20:S199-S217

Ulnar Nerve

Osborne fascia

Arcuate ligament

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Technique: cubital tunnel

OlecranonMedEpicond

FCUh FCUu

Arcuate Ligament

Distal

Ulnar Nerve: cubital tunnel syndrome

• Enlarged1 >9.5 mm2

• Hypoechoic• Causes:

– Idiopathic, overuse– Joint process, intra-articular body– Anconeus epitrochlearis:

• Normal variant accessory muscle

1Thoirs, J Ultrasound Med 2008; 27:737

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Cubital Tunnel Syndrome

Arcuate Ligament

Anconeus Epitrochlearis

Olecr

Med Epicond

Ulnar Nerve

Transverse

Transverse

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Ulnar Nerve Dislocation

• Occurs in elbow flexion

• Reduces in extension

• Nerve irritation, predisposes to injury

• Found in 20% asymptomatic volunteers

Okamoto, J Hand Surg 2000; 25B:85

Technique: ulnar nerve subluxation

Transverse

OE ET

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Isolated Ulnar Nerve Dislocation

Short Axis

Medial Epicondyle

Apex

Ulnar Nerve

Snapping Triceps Syndrome: dynamic imaging

Anterior Posterior

Transverse

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Nerve Entrapment Syndromes

• Radial:– Supinator syndrome

– Wartenberg syndrome• Superficial sensory branch radial nerve

• Suprascapular: paralabral cyst

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Radial Nerve

Radial Nerve Bifurcation

Brachoradialis BTArt

Brachialis

Pronator Teres

Median Nerve

Supinator Syndrome

Abnormal Normal

HumerusRadius

Supinator

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Supinator Syndrome

Transverse

Abnormal

Normal

RadialHead

RHBrachioradialis

Deep Br.Superficial Br.

Nerve Entrapment Syndromes

• Radial:– Supinator syndrome

– Wartenberg syndrome• Superficial sensory branch radial nerve

• Suprascapular: paralabral cyst

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Wartenberg Syndrome:

• Superficial branch of radial nerve– Sensory branch– Crosses over distal radius and first wrist

compartment

• Entrapment• Injury: direct trauma, iatrogenic

Wartenberg Syndrome

Transverse

TT

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Radial Nerve, Superficial Branch InjuryPost-operative distal radius fracture

Longitudinal Transverse

HematomaRadiusScrew

Nerve Entrapment Syndromes

• Radial:– Supinator syndrome

– Wartenberg syndrome• Superficial sensory branch radial nerve

• Suprascapular: paralabral cyst

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Labral Cyst:

• Most associated with labral tear• Suprascapular notch:

– Supraspinatus and infraspinatus atrophy

• Spinoglenoid notch:– Infraspinatus atrophy

• US guided aspiration

Labral Cyst: infraspinatus atrophy

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Nerve Entrapment Syndromes

• Peroneal:– Common peroneal

– Superficial peroneal

• Tibial

• Interdigital (Morton neuroma)

Anatomy: lateral

From: Netter’s Atlas of Human Anatomy

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Common Peroneal Nerve: entrapment

Long Axis

Fibula

Peroneus Longus

Peroneal Intraneural Ganglion

• Joint fluid from proximal tibiofibular joint– Enters peroneal nerve via articular nerve

branches

– Shown at MR arthrography after exercise

– Extends proximal via epineurial sheath1

• May also form via tibial nerve2

1Spinner et al. Clin Anatomy 2007; 20:8262Spinner et al. Skeletal Radiol 2006; 35:172

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Peroneal Intraneural Ganglia

From: Spinner et al. Skeletal Radiol 2008;37:1091

From: Spinner et al. Clin Anatomy 2007;20:826

Peroneal Intraneural Ganglion

Fibula

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Intraneural Ganglion

>15 cm

Atrophy Asymptomatic

Nerve Entrapment Syndromes

• Peroneal:– Common peroneal

– Superficial peroneal

• Tibial

• Interdigital (Morton neuroma)

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Superficial Peroneal Nerve

• Pierces crural fascia of leg:

– 9.2 cm proximal to fibular tip

– Range: 6 to 16 cm proximal

– Potential entrapment site

• Terminal branches: 6 cm proximal to fibular tip

– Superficial to inferior extensor retinaculum

Canella, AJR 2009; 193:174

Superficial Peroneal Nerve

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Muscle Hernia (extensor digitorum):superficial peroneal nerve entrapment

Longitudinal

Nerve Entrapment Syndromes

• Peroneal:– Common peroneal

– Superficial peroneal

• Tibial

• Interdigital (Morton neuroma)

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Tarsal Tunnel:

• Osteofibrous tunnel: medial ankle• Tibial nerve• Tendons: tibialis posterior, flexor

digitorum longus, flexor hallucis longus

• Entrapment: mass, ganglion

From: Martinoli, RadioGraphics 2000; 20:S199

Tarsal Tunnel Syndrome

• Entrapment of tibial nerve– Ganglion cyst: most common– Varicose veins, tenosynovitis– Trauma, deformity, coalition, idiopathic

• Tibial nerve:– May appear normal– May be hypoechoic and swollen

Nagaoka, J Ultrasound Med 2005;24:1035

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Ganglion Cyst: tarsal tunnel syndrome

Axial Sagittal

F P

FHL

Nerve Entrapment Syndromes

• Peroneal:– Common peroneal

– Superficial peroneal

• Tibial

• Interdigital (Morton neuroma)

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Morton Neuroma:

• Digital nerve entrapment– Common plantar digital nerve

• Edema, fibrosis, necrosis• 3rd intermetatarsal space > 2nd

• Sharp, burning pain from metatarsal head to toes

• Females: pliable foot, high-heeled narrow-toed shoes From: Martinoli,

RadioGraphics 2000; 20:S199

Morton Neuroma:

• Hypoechoic 5 mm mass

– Sensitivity: 100% ; Specificity: 83%

• Digital nerve continuity*

– Excludes other causes for mass

• Compression:

– Produces symptoms

– Bursa (compressible) vs. neuroma (not compressible)

Redd et al. Radiology 1989; 171:415Quinn et al. AJR 2000; 174:1723

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Morton Neuroma

Transverse Coronal T1w

MT

MT

Morton Neuroma

Plantar

Plantar

Dorsal

Dorsal

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Dynamic Evaluation:

• Mulder’s clinical test– Compression of metatarsal heads– Lateral to medial– Produces palpable click

• Sonographic Mulder Sign– Scan from plantar: coronal plane– Neuroma displaces: plantar

– Palpable click

Torriani, AJR 2003; 180:1121

Dynamic imaging: Mulder’s Maneuver

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Summary: peripheral nerve US

• Resolution better than MRI

• Evaluate entire limb efficiently

• Easy comparison to contralateral side

• Direct correlation: signs and symptoms

• Dynamic imaging