Copyright ©The Author(s) 2020.
World J Radiol. Jun 28, 2020; 12(6): 101-129
Published online Jun 28, 2020. doi: 10.4329/wjr.v12.i6.101
Table 1 Characteristic ultrasound findings in entrapment neuropathies
Median neuropathy at the wrist – CTSIncreased CSA at the distal wrist crease[68]Reduced median nerve echogenicity proximal to compression site both with[77,78] and without EDX abnormalities in 82.4%[79]Increased median nerve vascularity, with[65] and without EDX abnormalities in 7.1%[79]Reduced median nerve mobility (transverse and longitudinal) with[77,80,81] and without EDX abnormalities in 75%[79]
Range ULN 8.5-12 mm2[69-73]In CTS confirmed on EDX:[65]Reduced transverse sliding of the median nerve correlated with presence of CTS and severity of CTS[82,83]
Using ULN of 8.5-10 mm2 for the diagnosis of CTS[74]Loss of fascicular architectureSensitivity 95%Improved mobility post steroid injection[78]
Sensitivity 65%-97%, Specificity 72.7%-98%, PPV 79%-97%Specificity 71%Increased Median nerve stiffness - seen with all elastography modalities[51]:
WFR > 1.4[68]PPV 94%Correlates with severity[84,85]
Comparing 12 cm proximal to the distal wrist creaseImproves post steroid injection[78]Stiffness decreases after CTS release[86] and steroid injections[87]
Sensitivity 100% (Specificity NA)Identify anomalous anatomy:
US parameters suggested for the presence of CTS with normal EDX[66]:Bifid median nerve 5%-10%[88-90]
CSA > 14 mm2Persistent median artery 0.5%-3.7%[88,90]
WFR > 1.8Anomalous muscles in the carpal tunnel[91]
In CTS with a negative US at the distal wrist crease, 25% have CSA enlargement in the distal carpal tunnel.
Scanning the whole carpal tunnel increases sensitivity by 15%-20%[75,76]
UNEIncreased CSA, maximal at medial epicondyleReduced nerve echogenicity and increased nerve hypoechoic fraction[22,98]Intraneural vascularisation[100,101]Ulnar nerve subluxation with elbow flexion in 14%-23.1%; dislocation across the medial epicondyle in 8.5%[94]
ULN 8-11 mm2, most commonly 10 mm2[92-96]Hypoechoic fraction increased distal and proximal to the medial epicondyle[98]Present in 15%Ulnar nerve dislocation and symptomatic UNE can be found in the context of negative EDX findings
Using the following cut-off values for UNE:Correlated with axonal loss, atrophy and increased CSAHighest diagnostic yield is in patients with EDX abnormalities, but unable to localise - diagnosis confirmed by US in 86%[93]
> 9 mm2 - Sensitivity 84%, Specificity 80%[97]Alternative locations for entrapment
> 11 mm2 - Sensitivity 95%, Specificity 71%[95]Arcade of Struthers[102]
Note: Maximal CSA may not be at the site of EDX abnormality[98]Wrist[103]
Increased ratio of nerve CSA at elbow compared with arm or forearm[95,96,98,99]Identification of alternate aetiologies[104-112], e.g. trauma, brachial artery occlusion, scar tissue, haematoma, subdermal implants, venepuncture, ganglion cysts, anconeus epitrochlearis muscle
Upper arm swelling ratio > 2.1[96]Guide management[113,114]
Max CSA/ Mid-upper arm CSACubital tunnel – entrapment – benefits surgical decompression
Sensitivity 60%, Specificity 74%Epicondylar groove – external compression or stretching – no benefit from surgery
Forearm swelling ratio > 2.3[96]
Max CSA/ Mid-forearm CSA
Sensitivity 65%, Specificity 79%, PPV 89.2%
Radial neuropathy at the spiral groove or PINIncreased CSA[16,66,115,116]:Loss of echogenicity with PIN at level of maximal CSA[117]Intraneural hypervascularity at site of compression[118]Loss of fascicular structure with PIN at site of maximal CSA[117]
Radial nerve in spiral groove and antecubital fossa – ULN 9-10 mm2Provides additional information complementing EDX in 84%[116]
Posterior interosseous nerve – ULN 1-2 mm2
Superficial radial nerve - ULN 1-3 mm2
Common peroneal neuropathy at fibular headIncreased CSA at fibular headLoss of echogenicity at the site of maximal compression, with and without a normal CSA[121,124]NASensitivity for diagnosis[125]: 90% (95%CI, 79.7%- 97.3%)
ULN 8-14 mm2, commonly 11 mm2[16,119-122]US localisation[120]:
Using the following cut-off values for the common peroneal nerve at the fibular head:Fibular head 55%
> 8 mm2 - Sensitivity 90%, Specificity 69%[120]Above fibular head 71%
> 11.5 mm2 - Sensitivity 89%, Specificity 99%[121]Addition of US to EDX allowed for localisation in 88%, compared with 65.5% EDX alone[120]
Suggested cut-offs:Alternate aetiology[16,126,127]:
8 mm2 if abnormal EDX[120]Ganglion cysts (18% of cases) lipomas, scar tissue after knee surgery, abnormal biceps femoris anatomy
11 mm2 for normal EDX[120]Guides requirement for surgical intervention[128]
CSA may be normal if conduction block, but no axonal loss, on EDX[123]
LCFN - MPIncreased CSA at anterior superior iliac spine[129,130]Intraneural hypoechogenicity[129]NAAnatomical variants in 20%[131]
4-5 mm2[129,130]LFC nerve closer to/lateral to the Anterior superior iliac spine in patients with idiopathic MP[132,133]
ULN 5 mm2 – Sensitivity 95.7%, Specificity 95.5%, PPV 95.7%[130]Neuroma[131]
Increased nerve diameter
4 mm[129]
Tibial neuropathy - TTS or Proximal tibial neuropathyIncreased CSA at or distal to the tarsal tunnel (cf. median nerve) can be seen in the[134]:Intraneural and fascicular hypoechogenicity[135]NAIdentification of underlying aetiology of TTS
Tibial nerve, Medial plantar and Lateral plantar nervesUltrasound identifies 60-80%[136,137]
Using the following cut-off values for the tibial nerve within the tarsal tunnel[134]:Preoperative US assessment identifies[136,138-140]: Ganglia (7-58%), Talocalcaneal coalition +/- ganglia, Varicose veins (18- 6%), Accessory soleus and flexor digitorum muscles (6%)
> 19 mm2 - Sensitivity 61%, Specificity 88%Multiple sites of compression frequently seen in the tarsal tunnel and more distal or proximal[137]
Within tunnel-to-proximal tunnel CSA ratio > 1[134]Identification of underlying aetiology in proximal tibial neuropathies[141-143]: Baker’s cysts, intraneural ganglion cysts, deep vein thrombosis, popliteal artery aneurysms, soleal sling
Measured within the tarsal tunnel, proximal and inferior to the medial malleolus, and 4 cm proximal at the upper border of the medial malleolus
Sensitivity 74%, Specificity 100%
Best to compare CSA to contralateral side
Neurogenic thoracic outlet syndromeEnlarged CSA of lower trunk of the brachial plexus[144]Hypoechogenicity of the lower trunk of brachial plexus[144]NAAlternate aetiologies[144-147]:
Affected - 32.5 mm2 (range: 20-50 mm2)Loss of fascicular structure[144]Cervical rib
Controls – 16.7 mm2 (range: 9-23 mm2)Hyperechoic fibromuscular band (wedge shaped) adjacent to the middle scalene muscle – indenting the lower trunk of the brachial plexus (sickle shaped)[144]Anomalous muscular insertion (scalene muscle between subclavian artery and brachial plexus)
“Wedge-sickle” signBrachial plexus branching variants
Sensitivity 95%, PPV 82.6%Subclavian arterial occlusion with dynamic movement
Sonographic Tinel’s sign[144]
Sensitivity of 55% (95% CI: 31.53%–76.94%)
PPV of 100% (95% CI: 71.51%–100.00%)