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Ultrasound of carpal tunnel syndrome
Samir Haffar MD
Internal medicine – Ultrasound
Ultrasound of carpal tunnel syndrome (CTS)
① Diagnosis of carpal tunnel syndrome
② Ultrasound of normal carpal tunnel
③ Ultrasound features of carpal tunnel syndrome
④ Ultrasound of space occupying lesions in carpal tunnel
⑤ Advanced technique: elastography of median nerve
⑥ Ultrasound for poor outcome after carpal tunnel release
CTS: carpal tunnel syndrome
① Diagnosis of carpal tunnel syndrome
Diagnosis of carpal tunnel syndrome
Extremely common (3 – 5% of the general population)
• Symptoms
• Physical examination
• Electrodiagnostic studies: nerve conduction study – EMG
• Imaging modalities: high frequency US – MRI
EMG: eletromyography – MRI: magnetic resonance imaging – US: ultrasound
Symptoms of carpal tunnel syndrome
• Intermittent pain & paresthesias in distribution of median nerve:
Hallmarks of carpal tunnel syndrome
1st to 3rd finger & radial half of 4th finger
Symptoms vary: localize to wrist/hand, radiate to forearm/shoulder
Disappearance of pain is late finding: permanent sensory loss
• Flick sign:
Patients awaken with symptoms & shaking hand for relief
• Provoking factors:
Tasks requiring repetitive wrist flexion or hand elevation: driving, ..
• Motor fibers affected in more severe cases:
Difficulty in holding objects, opening jars, or buttoning a shirt
Wipperman J et al. Am Fam Physician 2016;94(12):993–999.
Median nerve palmar distribution
Wipperman J et al. Am Fam Physician 2016;94(12):993–999.
Thumb, index finger, middle finger & radial half of ring finger
Physical examination in carpal tunnel syndrome
Examination of entire upper extremity to exclude other causes
• Mild to moderate cases:
Most patients will not have physical examination findings
• More severe disease: permanent sensory & motor deficits
- Phalen test, Carpal compression test, Tinel test, Weber test
- Hyoalgesia: decreased sensation to pain on palmar aspect of index
Sensation over thenar eminence should be normal
- Weakness of thumb abduction and opposition
- Atrophy of thenar eminence in advanced cases
Wipperman J et al. Am Fam Physician 2016;94(12):993–999.
Phalen test
Holding the wrist in maximal flexion for up to 60 sec
Numbness & paresthesia on first three fingers is considered positive
Sensibility: 57 to 68% – Specificity: 58 to 73%
In: Carpal tunnel syndrome and related median neuropathies: Challenges and complications.
S. Duncan & R. Kakinoki (Eds), Springer International Publishing, 2017.
It is possible to test both sides by asking patient to place
both hands back to back while flexing the wrists
and dropping elbows to increase degree of wrist flexion
Phalen test
Middleton SD & Anakwe RE. BMJ 2014;349:g6437.
Carpal compression test
Durkan’s test
Apply direct pressure with thumb on carpal tunnel for 1 min
Paresthesia in median nerve distribution is considered positive
Sensibility: 64% – Specificity: 83%
In: Carpal tunnel syndrome and related median neuropathies: Challenges and complications.
S. Duncan & R. Kakinoki (Eds), Springer International Publishing, 2017.
Tinel’s test
Repeated percussion over median nerve in a proximo-distal direction
Paresthesias in median nerve distribution is considered positive
Sensibility: 36 to 50% – Specificity: 77%
In: Carpal tunnel syndrome. R. Luchetti & P. Amadio (Eds.), Springer-Verlag, 2007.
Two-point discrimination test
Weber test
In: Carpal tunnel syndrome. R. Luchetti & P. Amadio (Eds), Springer-Verlag, 2007.
Generally normal in mild or moderate cases
Atrophy of thenar muscles
Present in advanced cases
Differential diagnoses of carpal tunnel syndrome
Few disorders to be considered
• Cervical radiculopathy:
Neck pain radiated to upper limb, reflexes lost or diminished
• Polyneuropathies (diabetes, hypothyroidism):
Symptoms relate to both arms & legs, reflexes lost or diminished
• Osteoarthritis of small joints of hand
Painful & stiff small joints of hand
• Inflammatory arthropathy of small joints of hand
Features of systemic disease as well as joint specific symptoms
• Motor neuron disease: usually no sensory component
• Ulnar nerve compression: paresthesias of ring & little fingers
Middleton SD & Anakwe RE. BMJ 2014;349:g6437.
Padua L et al. Lancet Neurol 2016;15: 1273–84.
These tests are considered to be more supportive
for the diagnosis where two or more of them show
abnormal results, but less reliable when used individually,
with wide variation in reported sensitivity & specificity
Middleton SD & Anakwe RE. BMJ 2014;349:g6437.
With careful history taking and some simple clinical
function tests, a neurologist or family physician may
arrive at a definite diagnosis in > 80% of cases
Seror P. Eur J Radiol 2008;67:146–152.
Electrodiagnostic testing
Definition of site and extent of damage along course of the nerve
• Indications: Confirming carpal tunnel syndrome in atypical cases
Excluding radiculopathy, poly- & mononeuropathies
Before surgery: confirm diagnosis & assess severity
More severe cases less likely to recover after surgery
• Accuracy: Sensitivity: 56-85% – Specificity: 94-99%
May be normal in up to one-third of mild cases
• Limitations: Uncomfortable for patients and time consuming
Wipperman J et al. Am Fam Physician 2016;94(12):993–999.
Ultrasound in carpal tunnel syndrome
• Prerequisites: High resolution state-of-the-art machine
High frequency transducer
Good operator experience
• Advantages: Low cost, noninvasive, well tolerated by patients
Assess median nerve: size, blood flow, mobility
Accurate: high sensibility and specificity
Reproducible: good intra- & inter-observer agreement
Diagnosis of space occupying lesions in carpal tunnel
Can assess severity
• Limitations: Cannot rule out etiologies such as polyneuropathies
Wipperman J et al. Am Fam Physician 2016;94(12):993–999.
Two types of carpal tunnel syndrome
• Idiopathic: Most cases
• Secondary:
Pregnancy: Edema & hormonal alterations
Type 1 & 2 DM: Pooled odds ratio 1.97
Obesity: Increase risk by two times
Hypothyroidism: Modest association
Overuse of hand or wrist: Computer use (keyboard and mouse)
Space occupying lesions: Tenosynovitis, ganglion cyst, lipoma, …
Inflammatory arthropathy
Renal failure
Wrist trauma
Middleton SD & Anakwe RE. BMJ 2014;349:g6437.
Carpal tunnel syndrome is anything but simple
It is a complex and diverse condition
Peer S et al. Imaging Med 2012;4(3):287–297.
② Ultrasound of normal carpal tunnel
Schematic drawing of carpal tunnel
Transverse section of carpal tunnel
Carpal tunnel contains median nerve
and nine flexor tendons of forearm
Carpal bones in wrist
Anatomy of carpal tunnel
• Floor: Carpal bones: Scaphoid & trapezium laterally
Pisiform & hook of hamate medially
• Contents: Flexor digitorum profundus tendons (FDP)
Flexor digitorum superficialis tendons (FDS)
Flexor pollicis longus tendon (FPL)
Median nerve (superficial to FPL tendon)
• Roof: Flexor retinaculum (carpal tunnel ligament)
Attaching to scaphoid & Trapezium laterally
Pisiform & hook of hamate medially
Flexor carpi radialis tendon located outside carpal tunnel
Brown JM et al. RadioGraphics 2016;36:452–463.
Cross-section of a normal peripheral nerve
Multiple axons grouped into fascicles
Surrounded by dense perineurial sheath
Multiple fascicles combine into individual nerve
Surrounded by a sheath of epineurium
Median nerve in distal forearm and wrist
• Distal forearm:
Between flexor digitorum superficialis & profundus
• Carpal tunnel:
Directly under flexor retinaculum
Superficial to flexor pollicis longus tendon & flexor of 2nd digit tendon
• Shape of median nerve in carpal tunnel:
Oval in initial segment – more flat at hook of hamate level
Olchowy C et al. J Ultrason 2017;17:123–128.
Transverse US of median nerve at distal forearm
Pronator quadratus (PQ) bridges radius (R) & ulna (U) longitudinally
FDS & FDP constitute bulk of superficial & deep compartments
Median nerve situated between these 2 compartments (triangle)
Ulnar neurovascular bundle (UNA) seen at same layer medially
FDS: flexor digitorum superficialis – FDP: flexor digitorum profundus
Chen YT et al. J Ultrasound Med 2016;35:e11–e24.
Carpal tunnel
A: carpal tunnel inlet
B: carpal tunnel outlet
AB
Scanning proximal & distal parts of carpal tunnel
Guyon canal assessed using similar transducer position as carpal tunnel
However, transducer should be slightly shifted to ulnar side
Olchowy C et al. J Ultrason 2017;17:123–128.
Sc: scaphoid
Ps: pisiform
Arrows: transverse carpal ligament
Solid triangle: median nerve
S: flexor digitorum superficialis tendons
P: flexor digitorum profundus tendons
FPL: flexor pollicis longus
FCR: flexor carpi radialis
Open triangle: ulnar nerve
U a/v: ulnar artery and vein
Chen YT et al. J Ultrasound Med 2016;35:e11–e24.
Transverse US of normal carpal tunnel at inlet
Transverse US of distal carpal tunnel at outlet
Flexor retinaculum is about 3 – 4 cm wide (arrows)
Inserts to trapezium radially & hook of hamate medially
Presazzi A et al. J Ultrasound 2011;14:40–46.
Transverse US of normal carpal tunnel at outlet
Chen YT et al. J Ultrasound Med 2016;35:e11–e24.
Floor of carpal tunnel: trapezium laterally & hook of hamate medially
Thenar & hypothenar muscles seen on each side
Ulnar artery slightly superficial & radial to hook of hamate
Flexor retinaculum may be difficult to appreciate
Median nerve (triangle) nearly entirely hypoechoic
Hyperechoic regions deep to median nerve are flexor tendons
Echotexture of normal median nerve
Peer S et al. Imaging Med 2012;4(3):287–297.
Transverse US of carpal tunnel in a healthy volunteer
Honeycomb appearance
Hypoechoic fascicles (short arrows)
Tiny hyperechoic layers divide one fascicle from the other
Surrounded by hyperechoic perineurium (long arrows)
Distinction between nerves and tendons
Transverse US of median nerve in a healthy volunteer
Hyperechoic to hypoechoic tendon by transducer tilt position (T)
Minimal change of median nerve (arrow)
Signal change of tendon caused by anisotropy effect
In: Atlas of peripheral nerve ultrasound with anatomic and MRI correlation.
S Peer & H Gruber (Eds), Springer-Verlag, 2013.
Normal median nerve proximal to and in carpal tunnel
MN: median nerve
T: flexor tendons in carpal tunnel
Lawande AD et al. Indian J Radiol Imaging 2014;24(3):254–258.
Longitudinal US of normal median nerve
Longitudinal ultrasound of median nerve
Chen YT et al. J Ultrasound Med 2016;35:e11–e24.
Median nerve (triangles) deep to transverse carpal ligament (TCL)
and superficial to flexor tendons (asterisks)
Capitate (C) is most prominent carpal bone, distal to lunate (L)
and proximal to third metacarpal (3MC)
Normal flexor retinaculum
Flexor retinaculum is flat or convex
Flexor retinaculum situated at level of line drawn
between trapezium (TR) and hook of hamate (H)
Absence of palmar bowing
Transverse US of carpal tunnel at outlet
Ng AWH et al. Clin Radiol 2018;73(2):214.e11–214.e18.
Transverse ultrasound of Guyon’s canal
Guyon canal contains ulnar artery (A), ulnar vein(V) & ulnar nerve (U)
Cross-sectional images of the nerve show sites of its division
into two branches: deep motor and superficial sensory branch
Olchowy C et al. J Ultrason 2017;17:123–128.
Anatomic variants of carpal tunnel
• Median nerve: Proximal bifurcation (3% of the general population)
Proximal trifurcation (extremely rare)
• Persistent median artery: 3% of the general population
• Intrusion of flexor digitorum superficialis into carpal tunnel
• Reversed palmaris longus
• Accessory muscles
Presazzi A et al. J Ultrasound 2011;14:40–46.
Numerous variants involving nerves, artery, tendons and muscles
Proximal bifurcation of median nerve
CTS: carpal tunnel syndrome – CSA: criss-sectional area
Peer S et al. Imaging Med 2012;4(3):287–297.
Bifid median nerve (arrows) & hyperechoic epineurium (arrowheads)
Diameters of 2 nerves vary considerably: generally they of same size
Might predispose to carpal tunnel syndrome
Transverse US of carpal tunnel in a healthy volunteer
Proximal trifurcation of median nerve
rare anatomic variant
Median nerve divided into three branches
Three nerves travelling in carpal tunnel
just below the flexor retinaculum (arrows)
Transverse US of carpal tunnel
Presazzi A et al. J Ultrasound 2011;14:40–46.
Persistent median artery
Prevalence 3% – Might predispose to carpal tunnel syndrome
Normal median nerve
with eccentric PMA
(37%)
High division of median nerve
with midline PMA
(44%)
Bifid median nerve
with midline PMA
(19%)
PMA: persistent median artery
Gassner EM et al. J Ultrasound Med 2002;21:455–461.
Persistent median artery and veins
Left image: bifid median nerve, persistent median A & V (arrowheads)
Right image: collapsed veins with light probe compression
Small image: color Doppler of artery and veins
Ekiz T et al. Am J Phys Med Rehabil 2016;
Transverse US of carpal tunnel in a healthy man
Reversed palmaris longus
Presazzi A et al. J Ultrasound 2011;14:40–46.
Tendon in proximal position
Muscle belly in distal position
May cause carpal tunnel syndrome
Reversed palmaris longus
Transverse US of carpal tunnel
Normal palmaris longus
Anatomic drawing
Muscle belly in proximal
position
Tendon in distal position
Muscle belly of flexor digitorum superficialis
in carpal tunnel
Presazzi A et al. J Ultrasound 2011;14:40–46.
Transverse US of carpal tunnel in a healthy man
Muscle belly of flexor digitorum superficialis in carpal tunnel
Normally only flexor digitorum tendons travel in carpal tunnel
This variant can cause carpal tunnel syndrome
③ Ultrasound features of carpal tunnel syndrome
Indications of US in carpal tunnel syndrome
• Complementary to electrodiagnostic testing for diagnosis
Equally suited for diagnosis as electrodiagnostic testing
• Diagnosis of space occupying lesions in carpal tunnel syndrome
• Poor outcome after carpal tunnel release
Peer S et al. Imaging Med 2012;4(3):287–297.
• Patient comfortably seated across from examiner
• Wrist on table at comfortable height in slight extension (10-20)
• Generous gel throughout distal arm to wrist
• Staying perpendicular to structure
• Areas examined: - Distal forearm: pronator quadratus
- Carpal tunnel: inlet, tunnel, outlet
• Dynamic tests
US protocol for carpal tunnel syndrome
US protocol for carpal tunnel syndrome
① Transverse US of distal forearm: CSA of median nerve
② Transverse US of carpal tunnel inlet: CSA of median nerve
③ Transverse US from tunnel to outlet: space occupying lesions
④ Longitudinal US of carpal tunnel: deformation of median nerve
⑤ Dynamic tests: thenar flexion stress test, muscle intrusion tests
CSA: cross-sectional area
Chen YT et al. J Ultrasound Med 2016;35:e11–e24.
With practice, this protocol evaluates carpal tunnel in < 90 sec
Areas to examine
Ultrasound features of carpal tunnel syndrome
• CSA of median nerve at maximum swelling: ≥ 10 mm2
• Wrist-to-forearm ratio of median nerve CSA : ≥ 1.4
• Inlet-to-outlet ratio of median nerve CSA: ≥ 1.3
• Intraneural vascularity of median nerve on Doppler
Peer S et al. Imaging Med 2012;4(3):287–297.
Commonly evaluated features
• Longitudinal compression of median nerve
• Increased flattening ratio of median nerve at pisiform/hamate level
• Loss of fascicular discrimination of medial nerve
• Thickened outer epineurium of median nerve
• Bowing of flexor retinaculum: ≥ 0.14
• Thickening of flexor retinaculum
Other evaluated features
Cross-sectional area of median nerve
Normal: 7 – 9.5 mm2
• Site: Level of maximum swelling of median nerve (preferred)
Proximal edge of flexor retinaculum (carpal tunnel inlet)
Level of pisiform bone
• Method: Direct tracing around inner border of epineurium
Accurate and reproducible
Better than ellipsoid method (irregular median nerve)
Chen YT et al. J Ultrasound Med 2016;35:e11–e24.
Direct tracing of median nerve around inner border
of epineurium at level of maximum swelling
Cross-sectional area of median nerve
Sagittal and transverse US of median nerve
CSA: cross-sectional area
Peer S et al. Imaging Med 2012;4(3):287–297.
Median nerve compressed under thickened retinaculum (arrowheads)
Area to measure CSA is proximal to upper edge of retinaculum (arrows)
CSA: 23 mm2 (normal < 10 mm2)
Cross-sectional area of median nerve at inlet > 10 mm2
is sensitive and specific for diagnosis of CTS
CTS: carpal tunnel syndrome
1 Cartwright MS et al. Muscle Nerve 2012; 46:287–293.
2 Torres-Costoso A et al. Arch J Phys Med Rehabi 2018:99(4):758-765.
Most validated ultrasound parameter
As accurate as electrodiagnostic tests for diagnosis 1
Sensibility 81% & specificity 84% in a recent meta-analysis 2
Wrist-to-forearm ratio of median nerve CSA
CSA at tunnel inlet/CSA 12 cm proximally
Level of pronator quadratus
Transverse US of median nerve
Level of tunnel inlet
CSA: cross-sectional area – FCR: flexor carpi radialis
Kapuścińska K et al. J Ultrasonography 2015;15:283–291.
CSA of median nerve at pronator quadratus : 10 mm2
CSA of median nerve at tunnel inlet: 18 mm2
Wrist-to-forearm ratio: 1.8 (normal < 1.4)
Inlet-to-outlet ratio of median nerve CSA
CSA at tunnel inlet/CSA at tunnel outlet
CSA: cross-sectional area – CTS: carpal tunnel syndrome
Fu T et al. PLoS ONE 2015;10(1): e0116777.
CSA of median nerve at tunnel inlet: 17 mm2
CSA of median nerve at tunnel outlet: 10 mm2
Inlet-to-outlet ratio: 1.7 (normal < 1.3)
Carpet tunnel inlet Carpet tunnel outlet
Transverse US of median nerve
Intraneural vascularity of median nerve
Systematic review: 7 studies – methodological shortcomings
• Doppler techniques: color, power and spectral
Power Doppler detects slow flow: best to detect intraneural flow
• Intraneural blood flow not detected by Doppler in healthy subjects
• Median sensitivity: 72% (range 41–95%)
Median specificity: 88% (range 71– 100%)
Good specificity interpreted with caution because of spectrum bias
• Advantages of Doppler: better tolerated than electrodiagnostic study
• Limitations of Doppler: operator dependent
Vanderschueren GA et al. Muscle Nerve 2014;50:159–63.
67-year-old male with left carpal tunnel syndrome
proven by nerve conduction studies & surgical findings
Transverse & longitudinal color Doppler US of median nerve
Hypervascularity of median nerve
At least one vessel ˃ 1 mm in length in sagittal or axial plane
Intraneural vascularity of median nerve
Ooi CC et al. Skeletal Radiol 214;43(10):1387–94.
In: Carpal tunnel syndrome and related median neuropathies.
SFM Duncan & R Kakinoki (Eds), Springer International Publishing, 2017.
Intraneural vascularity of median nerve
Median nerve enlargement
Intraneural vascularity on power Doppler (arrow)
Transverse power Doppler US of carpal tunnel
Intraneural vascularity of median nerve
Joy V et al. J Neurol Sciences 2011;308:16–20.
Particular value of Doppler in cases
of negative nerve conduction studies
Longitudinal US of median nerve at wrist
Color and Doppler spectral analysis
Longitudinal compression sign of median nerve
Compression of median nerve as it passes under retinaculum
C: Capitate – L: Lunate – R: Radius
Peer S et al. Imaging Med 2012;4(3):287–297.
Increased flattening of left
median nerve (arrows)
Longitudinal US of median nerve along carpal tunnel
Normal tapering of right medial
nerve inside carpal tunnel (arrow)
Left median nerve Right median nerve
Flatening ratio of media nerve
Ratio between the largest & smallest diameters of the nerve
CTS: carpal tunnel syndrome
Mani B et al. J Med Imag Rad Oncol 2011;55:126–131.
Largest diameter: 6.3 mm – Smallest diameter: 1.9 mm
Flattening ration of median nerve: 3.16
Normal value: 2.55 ± 0.54 at mid carpal tunnel
Overlaps with values in carpal tunnel syndrome patients
Largest diameter Smallest diameter
Loss of fascicular discrimination of medial nerve
Patient with severe carpal tunnel syndrome
Transverse US of median nerve
Peer S et al. Imaging Med 2012;4(3):287–297.
Loss of fascicular discrimination
CSA of median nerve at proximal edge of retinaculum: 54 mm2
Thickened outer epineurium of median nerve
Median nerve massively swollen
Thickened echoic outer epineurium (arrowheads)
Peer S et al. Imaging Med 2012;4(3):287–297.
Patient with longstanding severe carpal tunnel syndrome
Transverse ultrasound of carpal tunnel
Flexor retinaculum bowing ratio
Transverse US of carpal tunnel at outlet
Distance of palmar displacement (arrow)
Divided by distance between trapezium & hook of hamate (line)
f: flexor tendons – h: hook of hamate – t: trapezium
Normal ratio: 0 to 0.15 – Ratio in CTS: 0.14 to 0.26
Altinok T et al. Surg Radiol Anat 2004;26:501–503.
In: Carpal tunnel syndrome and related median neuropathies.
SFM Duncan & R Kakinoki (Eds), Springer International Publishing, 2017.
Thickening of flexor retinaculum
FR: flexor retinaculum
In: Carpal tunnel syndrome and related median neuropathies.
SFM Duncan & R Kakinoki (Eds), Springer International Publishing, 2017.
Transverse US of carpal tunnel inlet
Thickening of FR (arrow)
Enlarged median nerve (arrowhead
Enlarged median nerve
Cross-sectional area: 22.9 mm2
Dynamic US tests of carpal tunnel syndrome
Dynamic US tests of carpal tunnel syndrome
Chen YT et al. J Ultrasound Med 2016;35:e11–e24.
• Thenar flexion stress test: transverse & longitudinal view
Dynamic changes of median nerve caliber
• Flexor digitorum superficialis intrusion test: transverse view
Intrusion of flexor digitorum superficialis into carpal tunnel
• Lumbrical intrusion test: transverse view
Intrusion of lumbricals into carpal tunnel
Thenar digital flexion stress test
Chen YT et al. J Ultrasound Med 2016;35:e11–e24.
An object is placed in the hand of the patient
Patient apply gentle squeeze between thumb, index & middle finger
Transducer over median nerve
in long axis
Transducer over carpal tunnel
in transverse axis
Thenar digital flexion stress test
Relaxed view Stressed view
Longitudinal US of median nerve along carpal tunnel
Thenar muscle bulging into MN
Diameter of median nerve 0.7 mm
Median nerve diameter: 2 mm
Takata SC et al. J Diagn Med Sonogr 2019;35(1):62–68.
Thenar digital flexion stress test
Transverse US of carpal tunnel
Stressed viewRelaxed view
Thickness of median nerve decreases from 2.2 mm
to 1.4 mm (0.14 cm) during stress
36% “flattening” compression
Takata SC et al. J Diagn Med Sonogr 2019;35(1):62–68.
Flexor digitorum superficialis intrusion test
Aboul-fotouh M et al. Egyptian J Radiol Nuclear Med 2018;49:1060–1067.
Combined wrist and digit extension
Flexor digitorum superficialis intrusion test
FDS: flexor digitorum superficialis
Chen YT et al. J Ultrasound Med 2016;35:e11–e24.
Wrist & fingers extension
Flexor digitorum superficialis (*)
enters carpal tunnel and appearing
as hypoechoic mass
Transverse US of carpal tunnel
Normal carpal tunnel at rest
Relaxed wrist & fingers
median n median n
FDS
Chen YT et al. J Ultrasound Med 2016;35:e11–e24.
Patient asked to make a fist
Lumbricals are intrinsic muscles of hand that flex
metacarpophalangeal joints & extend interphalangeal joints
Lumbrical intrusion test
Transverse US of carpal tunnel
relaxed fingers
Lumbrical intrusion test
Chen YT et al. J Ultrasound Med 2016;35:e11–e24.
Transverse US of carpal tunnel
patient asked to make a fist
Normal carpal tunnel at rest Hypoechoic lumbrical enters carpal
tunnel and displacing median nerve
Small portion of lumbrical muscle
(white arrow) next to median
nerve (asterisk)
Takata SC et al. J Diagn Med Sonogr 2019;35(1):62–68.
Lumbrical intrusion test
Transverse US of carpal tunnel
Relaxed fingers
Transverse US of carpal tunnel
Patient asked to make a fist
Structure becomes enlarged
along with additional muscles
(white arrows)
Ultrasound assessment of CTS severity
Systematic review and meta-analysis
• Mild carpal tunnel syndrome:
Mean CSA of median nerve: 11.64 mm2 (95% CI: 11.23–12.05 mm2)
• Moderate carpal tunnel syndrome:
Mean CSA of median nerve: 13.74 mm2 (95% CI: 12.59–14.89 mm2)
• Severe carpal tunnel syndrome:
Mean CSA of median nerve: 16.80 mm2 (95% CI: 14.50–19.1 mm2)
CSA: cross-sectional area – CTS: carpal tunnel syndrome
Roomizadeh P et al. Am J Phys Med Rehabil 2019;98:373–381.
Compared to electrodiagnostic classification of CTS severity
Ultrasound can assess severity of CTS
④ US of space occupying lesions in carpal tunnel
External compression of median nerve
Rare cause of carpal tunnel syndrome: 2 – 3.5%
Space occupying lesions & carpal tunnel syndrome
• Tenosynovitis
• Ganglion cyst
• Bifid median nerve
• Vascular anomalies: persistent median a. – thrombosed median a.
• Tumors: hematoma – lipoma – neuroma
• Rheumatoid arthritis: rheumatoid nodule
• Gouty tophus
• Calcified nodule
• Accessory muscles
Peer S et al. Imaging Med 2012;4(3):287–297.
External compression of median nerve
Tenosynovitis
Peer S et al. Imaging Med 2012;4(3):287–297.
Transverse ultrasound of carpal tunnel
Patient with carpal tunnel syndrome
Marked hypoechoic fluid collections (arrows) between
mildly swollen flexor tendons diagnostic of tenosynovitis
Flattened median nerve (arrowheads)
Peer S et al. Imaging Med 2012;4(3):287–297.
Ganglion cyst
Patient with mild carpal tunnel syndrome
Large eccentric space occupying ganglion cyst (arrowheads)
abutting flexor tendons & dislocating median nerve (arrow)
Transverse US of carpal tunnel
Bifid median nerve
Hypoechoic enlargement of median nerve trunks (arrows)
proximal to carpal tunnel with transition to normal size
within carpal tunnel (arrowheads)
79-year-old woman with carpal tunnel syndrome
Jacobson JA et al. J Ultrasound Med 2016;35:683–693.
Transverse US of carpal tunnel Sagittal US of median nerve
Persistent median artery
Deniel A et al. Diag Interv Imaging 2015;96:1261–1278.
Persistent medial artery with bifid median nerve
Cross- sectional of of 2 components: 12 mm2
Median artery situated between the two nerves
Identification can be facilitated by color-Doppler examination
Patient with carpal tunnel syndrome
Transverse US of carpal tunnel Correspondent power Doppler US
Peer S et al. Imaging Med 2012;4(3):287–297.
Thrombosed median artery (arrow)
between fascicles of bifid median nerve (arrowheads)
Resection of artery resulted in improvement of symptoms
Transverse ultrasound of carpal tunnel
Thrombosed persistent median artery
Bouton C et al. Presse Med 2016;45:707.
Thrombosed persistent median artery
Transverse color Doppler US of carpal tunnel
Thrombosed median artery (A)
in the middle of bifid median nerve (N)
Intraneural hematoma of median nerve
Median nerve with
intraneural hematoma
Transverse US
of carpal tunnel
Intraoperative
photograph
Longitudinal US
of median nerve
Intraneural hematoma
(arrows)
Intraneural hematoma
(arrows)
Unterholzner V et al. Ultraschall Med 2012 Nov 5. DOI: 10.1055/s-0032-1325459.
66-year-old woman, acute CTS, no trauma or anticoagulant medication
Takes pressure at left wrist up to 20 times/d by wrist-measuring device
https://theultrasoundsite.co.uk/ultrasound-case-studies/lipoma-compressing-median-nerve-wrist/
Lipoma
50-year-old man, lump of right volar wrist, right hand paraesthesia
Indentation of median nerveLipoma in carpal tunnel
Transverse US of carpal tunnel Longitudinal US of median nerve
Nerve sheath tumor
Nerve sheath tumor of median nerve (yellow arrow)
R: radius – L: lunate
In: Carpal tunnel syndrome and related median neuropathies.
SFM Duncan & R Kakinoki (Eds), Springer International Publishing, 2017.
Patient with carpal tunnel syndrome
Longitudinal and transverse US of carpal tunnel
Nerve sheath tumor
Patient with carpal tunnel syndrome
Longitudinal and transverse US of carpal tunnel
Oval-shaped homogenous hypoechoic tumor (arrows)
arising from median nerve (dashed arrows)
Rhumatoid nodule
Patient with long-standing rheumatoid arthritis & unilateral CTS
Transverse US of carpal tunnel Sagittal US of median nerve
Hypoechoic nodule (open arrows)
adjacent to and dislocating median nerve (dashed arrows)
Gouty tophus
Echogenic structures in radiocarpal joint in carpal tunnel floor (arrows)
Marked flattening of median nerve at distal tunnel (*)
Aggregates of pseudogout crystals at surgery
Ooi CC et al. Skeletal Radiol 2014;43(10):1387–94.
62-year-old male, fullness in right wrist, numbness of first 3 digits
Transverse US of carpal tunnel Sagittal US of carpal tunnel
Calcified nodule in carpal tunnel
Cheng TF et al. Frontiers Neurol 2019;10: article 224.
Transverse US of carpal tunnel Sagittal US of carpal tunnel
Hyperechoic ovoid lesion occupying the carpal tunnel
with obvious median nerve compression
Grayish calcified nodule on pathological findings
Usefulness of US to rule out space occupying lesions
in carpal tunnel is one of main reasons why we should
perform it in every patient suspected of having CTS
CTS: carpal tunnel syndrome
Peer S et al. Imaging Med 2012;4(3):287–297.
⑤ Advanced technique: median nerve elastography
Techniques of elastography
World federation of ultrasound in medicine & biology
• Strain elastography:
Qualitative: results in color map
Degree of strain converted into color map superimposed on US image
• Aacoustic radiation force impulse (ARFI):
Qualitative & quantitative
Point shear wave elastography (pSWE): results in m/sec
Two dimensions shear wave elastography (2D SWE): results in kPa
kPa: kilopascal
Ferraioli G et al. Ultrasound Med Biol 2018;44(12):2419–2440.
Strain elastography of median nerve
In: Carpal tunnel syndrome and related median neuropathies.
SFM Duncan & R Kakinoki (Eds), Springer International Publishing, 2017.
Healthy volunteer
Normal size median nerve (yellow arrowhead)
Color mapping on elastography indicating soft nerve (red)
Enlarged median nerve (yellow arrowhead)
Color mapping on elastography indicating stiff nerve (blue)
Strain elastography of median nerve
In: Carpal tunnel syndrome and related median neuropathies.
SFM Duncan & R Kakinoki (Eds), Springer International Publishing, 2017.
Patient with carpal tunnel syndrome
2D shear wave elastography of median nerve
Kantarci F et al. Eur Radiol 2014;24:434–440.
Color box in proximal carpal tunnel
Yellow to red stiff flexor tendons – Non-stiff blue median nerve
Region of interest for SWE measurement includes just the median nerve
Mean elasticity of median nerve: 35.1 kPa
Healthy volunteer
Longitudinal US of median nerve along carpal tunnel
2D shear wave elastography of median nerve
Kantarci F et al. Eur Radiol 2014;24:434–440.
Patient with moderate carpal tunnel syndrome
Longitudinal US of median nerve along carpal tunnel
Mean elasticity of median nerve: 54.3 kPa
R: distal radius – C: proximal carpal row (lunate)
2D shear wave elastography of median nerve
Kantarci F et al. Eur Radiol 2014;24:434–440.
Patient with severe carpal tunnel syndrome
Longitudinal US of median nerve along carpal tunnel
Mean elasticity of median nerve: 130.9 kPa
R: distal radius – C: lunate
• 17 studies: 820 wrists with CTS and 581 asymptomatic wrists
Strain elastography: 13 studies – 2D SWE (4 studies)
• Median nerve at wrist stiffer in CTS than those in healthy controls
• Shear wave elastography more sensitive than strain elastography
to discriminate between patients with CTS and those without
• Ultrasound elastography revealed its potential in differentiating
CTS of different severity
Elastography of medial nerve in CTS
Systematic review and meta-analysis
CTS: carpal tunnel syndrome – 2D SWE: two dimensions shear wave elastography
Lin CP et al. Ultrasound Med Biol 2019 Aug 9. doi: 10.1016/j.ultrasmedbio.2019.07.409.
⑥ Ultrasound after carpal tunnel release
Poor outcome after carpal tunnel release
Causes of unfavorable outcome
• Extension of flexor digitorum muscle bellies into carpal tunnel
• Incomplete dissection of flexor retinaculum
• Hematoma
• Soft tissue infection
• Scar formation
• Traumatic neuroma
Peer S et al. Imaging Med 2012;4(3):287–297.
Flexor digitorum muscle bellies in carpal tunnel
Castillo R et al. Arch plastic Surg 2018;45(5):474–478.
Aberrant distal extension of flexor
digitorum muscle belly into carpal
tunnel which can result in crowding
of carpal tunnel & recurrence of
symptoms of carpal tunnel
Castillo R et al. Arch plastic Surg 2018;45(5):474–478.
Flexor digitorum muscle bellies in carpal tunnel
Extension of second flexor muscle belly (arrow)
into carpal tunnel in proximity to median nerve (asterisk)
Recurrent carpal tunnel syndrome 20 years after release
Longitudinal & transverse US of carpal tunnel
Incomplete dissection of flexor retinaculum
Tan TC et al. Hand Surgery 2011;16(3):289–294.
Patient with poor outcome after carpal tunnel release
Longitudinal ultrasound of median nerve
Indentation onto the median nerve
Peer S et al. Imaging Med 2012;4(3):287–297.
Soft-tissue infection
Hypertrophic inflamed subcutaneous tissue (arrows)
invading the median nerve (arrowheads)
Patient with poor outcome after carpal tunnel release
Transverse US of carpal tunnel
Patient with poor outcome after carpal tunnel release
Transverse US of carpal tunnel
Peer S et al. Imaging Med 2012;4(3):287–297.
Compression of median nerve (arrowheads)
by hypertrophic scar formation (arrows)
Hypertrophic scar
Enlarged median nerve (arrowhead)
Surrounding scar tissue (arrow)
In: Carpal tunnel syndrome and related median neuropathies.
SFM Duncan & R Kakinoki (Eds), Springer International Publishing, 2017.
Hypertrophic scar
Patient with poor outcome after carpal tunnel release
Transverse US of carpal tunnel
Asymptomatic right wristSymptomatic left wrist
Normal median nerve
(arrowhead
Traumatic neuroma
Normal appearance of posterior fascicles (arrows)
Hypoechoic post-traumatic neuroma of anterior part of nerve (N)
In-continuity neuroma of median nerve
Patient with poor outcome after carpal tunnel release
Transverse US of carpal tunnel
Depaoli R et al. J Ultrasound 2015;18:83–85.
Traumatic neuroma
Patient with poor outcome after carpal tunnel release
Longitudinal and transverse US of median nerve
Focal hypoechoic swollen region
Continuous proximally & distally with normal median nerve
Located 2–3 cm proximal to wrist crease
Cross-sectional area: 20.3 mm2
N: nerve
Chen KH et al. Am J Phys Med Rehabil 2009;88;771–774.
Sonography should be performed in every patient with
poor outcome after surgery or conservative treatment
Conclusion
• State-of-the-art machine, high frequency transducer & good
operator experience are prerequisites for ultrasound in CTS
• US is cheap, noninvasive, accurate and reproducible imaging
modality for the diagnosis of CTS and its severity
• Space occupying lesions of carpal tunnel is one of the main
reasons to perform ultrasound in every patient with CTS
• Ultrasound elastography can assess severity of CTS
• Ultrasound is useful in poor outcome after carpal tunnel release
CTS: carpal tunnel syndrome
Thank You
• Sensibility: 81% (95% CI: 74–88)
• Specificity: 84% (95% CI: 78–90)
• Positive likelihood ratio: 6.22 (95% CI: 3.99–9.71)
• Negative likelihood ratio: 0.16 (95% CI: 0.11–0.26)
• Diagnostic odds ratio: 31.11 (95% CI: 20.42–47.40)
CSA of median nerve in carpal tunnel syndrome
Most commonly evaluated parameter
CSA: cross-sectional area
Torres-Costoso A et al. Arch Phys Med Rehabi 2018;99(4):758–765.
Diagnostic accuracy of CSA at inlet from 9 to 12.5 mm2
Systematic review and meta-analysis

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Ultrasound of carpal tunnel syndrome

  • 1. Ultrasound of carpal tunnel syndrome Samir Haffar MD Internal medicine – Ultrasound
  • 2. Ultrasound of carpal tunnel syndrome (CTS) ① Diagnosis of carpal tunnel syndrome ② Ultrasound of normal carpal tunnel ③ Ultrasound features of carpal tunnel syndrome ④ Ultrasound of space occupying lesions in carpal tunnel ⑤ Advanced technique: elastography of median nerve ⑥ Ultrasound for poor outcome after carpal tunnel release CTS: carpal tunnel syndrome
  • 3. ① Diagnosis of carpal tunnel syndrome
  • 4. Diagnosis of carpal tunnel syndrome Extremely common (3 – 5% of the general population) • Symptoms • Physical examination • Electrodiagnostic studies: nerve conduction study – EMG • Imaging modalities: high frequency US – MRI EMG: eletromyography – MRI: magnetic resonance imaging – US: ultrasound
  • 5. Symptoms of carpal tunnel syndrome • Intermittent pain & paresthesias in distribution of median nerve: Hallmarks of carpal tunnel syndrome 1st to 3rd finger & radial half of 4th finger Symptoms vary: localize to wrist/hand, radiate to forearm/shoulder Disappearance of pain is late finding: permanent sensory loss • Flick sign: Patients awaken with symptoms & shaking hand for relief • Provoking factors: Tasks requiring repetitive wrist flexion or hand elevation: driving, .. • Motor fibers affected in more severe cases: Difficulty in holding objects, opening jars, or buttoning a shirt Wipperman J et al. Am Fam Physician 2016;94(12):993–999.
  • 6. Median nerve palmar distribution Wipperman J et al. Am Fam Physician 2016;94(12):993–999. Thumb, index finger, middle finger & radial half of ring finger
  • 7. Physical examination in carpal tunnel syndrome Examination of entire upper extremity to exclude other causes • Mild to moderate cases: Most patients will not have physical examination findings • More severe disease: permanent sensory & motor deficits - Phalen test, Carpal compression test, Tinel test, Weber test - Hyoalgesia: decreased sensation to pain on palmar aspect of index Sensation over thenar eminence should be normal - Weakness of thumb abduction and opposition - Atrophy of thenar eminence in advanced cases Wipperman J et al. Am Fam Physician 2016;94(12):993–999.
  • 8. Phalen test Holding the wrist in maximal flexion for up to 60 sec Numbness & paresthesia on first three fingers is considered positive Sensibility: 57 to 68% – Specificity: 58 to 73% In: Carpal tunnel syndrome and related median neuropathies: Challenges and complications. S. Duncan & R. Kakinoki (Eds), Springer International Publishing, 2017.
  • 9. It is possible to test both sides by asking patient to place both hands back to back while flexing the wrists and dropping elbows to increase degree of wrist flexion Phalen test Middleton SD & Anakwe RE. BMJ 2014;349:g6437.
  • 10. Carpal compression test Durkan’s test Apply direct pressure with thumb on carpal tunnel for 1 min Paresthesia in median nerve distribution is considered positive Sensibility: 64% – Specificity: 83% In: Carpal tunnel syndrome and related median neuropathies: Challenges and complications. S. Duncan & R. Kakinoki (Eds), Springer International Publishing, 2017.
  • 11. Tinel’s test Repeated percussion over median nerve in a proximo-distal direction Paresthesias in median nerve distribution is considered positive Sensibility: 36 to 50% – Specificity: 77% In: Carpal tunnel syndrome. R. Luchetti & P. Amadio (Eds.), Springer-Verlag, 2007.
  • 12. Two-point discrimination test Weber test In: Carpal tunnel syndrome. R. Luchetti & P. Amadio (Eds), Springer-Verlag, 2007. Generally normal in mild or moderate cases
  • 13. Atrophy of thenar muscles Present in advanced cases
  • 14. Differential diagnoses of carpal tunnel syndrome Few disorders to be considered • Cervical radiculopathy: Neck pain radiated to upper limb, reflexes lost or diminished • Polyneuropathies (diabetes, hypothyroidism): Symptoms relate to both arms & legs, reflexes lost or diminished • Osteoarthritis of small joints of hand Painful & stiff small joints of hand • Inflammatory arthropathy of small joints of hand Features of systemic disease as well as joint specific symptoms • Motor neuron disease: usually no sensory component • Ulnar nerve compression: paresthesias of ring & little fingers Middleton SD & Anakwe RE. BMJ 2014;349:g6437. Padua L et al. Lancet Neurol 2016;15: 1273–84.
  • 15. These tests are considered to be more supportive for the diagnosis where two or more of them show abnormal results, but less reliable when used individually, with wide variation in reported sensitivity & specificity Middleton SD & Anakwe RE. BMJ 2014;349:g6437.
  • 16. With careful history taking and some simple clinical function tests, a neurologist or family physician may arrive at a definite diagnosis in > 80% of cases Seror P. Eur J Radiol 2008;67:146–152.
  • 17. Electrodiagnostic testing Definition of site and extent of damage along course of the nerve • Indications: Confirming carpal tunnel syndrome in atypical cases Excluding radiculopathy, poly- & mononeuropathies Before surgery: confirm diagnosis & assess severity More severe cases less likely to recover after surgery • Accuracy: Sensitivity: 56-85% – Specificity: 94-99% May be normal in up to one-third of mild cases • Limitations: Uncomfortable for patients and time consuming Wipperman J et al. Am Fam Physician 2016;94(12):993–999.
  • 18. Ultrasound in carpal tunnel syndrome • Prerequisites: High resolution state-of-the-art machine High frequency transducer Good operator experience • Advantages: Low cost, noninvasive, well tolerated by patients Assess median nerve: size, blood flow, mobility Accurate: high sensibility and specificity Reproducible: good intra- & inter-observer agreement Diagnosis of space occupying lesions in carpal tunnel Can assess severity • Limitations: Cannot rule out etiologies such as polyneuropathies Wipperman J et al. Am Fam Physician 2016;94(12):993–999.
  • 19. Two types of carpal tunnel syndrome • Idiopathic: Most cases • Secondary: Pregnancy: Edema & hormonal alterations Type 1 & 2 DM: Pooled odds ratio 1.97 Obesity: Increase risk by two times Hypothyroidism: Modest association Overuse of hand or wrist: Computer use (keyboard and mouse) Space occupying lesions: Tenosynovitis, ganglion cyst, lipoma, … Inflammatory arthropathy Renal failure Wrist trauma Middleton SD & Anakwe RE. BMJ 2014;349:g6437.
  • 20. Carpal tunnel syndrome is anything but simple It is a complex and diverse condition Peer S et al. Imaging Med 2012;4(3):287–297.
  • 21. ② Ultrasound of normal carpal tunnel
  • 22. Schematic drawing of carpal tunnel
  • 23. Transverse section of carpal tunnel Carpal tunnel contains median nerve and nine flexor tendons of forearm
  • 25. Anatomy of carpal tunnel • Floor: Carpal bones: Scaphoid & trapezium laterally Pisiform & hook of hamate medially • Contents: Flexor digitorum profundus tendons (FDP) Flexor digitorum superficialis tendons (FDS) Flexor pollicis longus tendon (FPL) Median nerve (superficial to FPL tendon) • Roof: Flexor retinaculum (carpal tunnel ligament) Attaching to scaphoid & Trapezium laterally Pisiform & hook of hamate medially Flexor carpi radialis tendon located outside carpal tunnel Brown JM et al. RadioGraphics 2016;36:452–463.
  • 26. Cross-section of a normal peripheral nerve Multiple axons grouped into fascicles Surrounded by dense perineurial sheath Multiple fascicles combine into individual nerve Surrounded by a sheath of epineurium
  • 27. Median nerve in distal forearm and wrist • Distal forearm: Between flexor digitorum superficialis & profundus • Carpal tunnel: Directly under flexor retinaculum Superficial to flexor pollicis longus tendon & flexor of 2nd digit tendon • Shape of median nerve in carpal tunnel: Oval in initial segment – more flat at hook of hamate level Olchowy C et al. J Ultrason 2017;17:123–128.
  • 28. Transverse US of median nerve at distal forearm Pronator quadratus (PQ) bridges radius (R) & ulna (U) longitudinally FDS & FDP constitute bulk of superficial & deep compartments Median nerve situated between these 2 compartments (triangle) Ulnar neurovascular bundle (UNA) seen at same layer medially FDS: flexor digitorum superficialis – FDP: flexor digitorum profundus Chen YT et al. J Ultrasound Med 2016;35:e11–e24.
  • 29. Carpal tunnel A: carpal tunnel inlet B: carpal tunnel outlet AB Scanning proximal & distal parts of carpal tunnel Guyon canal assessed using similar transducer position as carpal tunnel However, transducer should be slightly shifted to ulnar side Olchowy C et al. J Ultrason 2017;17:123–128.
  • 30. Sc: scaphoid Ps: pisiform Arrows: transverse carpal ligament Solid triangle: median nerve S: flexor digitorum superficialis tendons P: flexor digitorum profundus tendons FPL: flexor pollicis longus FCR: flexor carpi radialis Open triangle: ulnar nerve U a/v: ulnar artery and vein Chen YT et al. J Ultrasound Med 2016;35:e11–e24. Transverse US of normal carpal tunnel at inlet
  • 31. Transverse US of distal carpal tunnel at outlet Flexor retinaculum is about 3 – 4 cm wide (arrows) Inserts to trapezium radially & hook of hamate medially Presazzi A et al. J Ultrasound 2011;14:40–46.
  • 32. Transverse US of normal carpal tunnel at outlet Chen YT et al. J Ultrasound Med 2016;35:e11–e24. Floor of carpal tunnel: trapezium laterally & hook of hamate medially Thenar & hypothenar muscles seen on each side Ulnar artery slightly superficial & radial to hook of hamate Flexor retinaculum may be difficult to appreciate Median nerve (triangle) nearly entirely hypoechoic Hyperechoic regions deep to median nerve are flexor tendons
  • 33. Echotexture of normal median nerve Peer S et al. Imaging Med 2012;4(3):287–297. Transverse US of carpal tunnel in a healthy volunteer Honeycomb appearance Hypoechoic fascicles (short arrows) Tiny hyperechoic layers divide one fascicle from the other Surrounded by hyperechoic perineurium (long arrows)
  • 34. Distinction between nerves and tendons Transverse US of median nerve in a healthy volunteer Hyperechoic to hypoechoic tendon by transducer tilt position (T) Minimal change of median nerve (arrow) Signal change of tendon caused by anisotropy effect In: Atlas of peripheral nerve ultrasound with anatomic and MRI correlation. S Peer & H Gruber (Eds), Springer-Verlag, 2013.
  • 35. Normal median nerve proximal to and in carpal tunnel MN: median nerve T: flexor tendons in carpal tunnel Lawande AD et al. Indian J Radiol Imaging 2014;24(3):254–258. Longitudinal US of normal median nerve
  • 36. Longitudinal ultrasound of median nerve Chen YT et al. J Ultrasound Med 2016;35:e11–e24. Median nerve (triangles) deep to transverse carpal ligament (TCL) and superficial to flexor tendons (asterisks) Capitate (C) is most prominent carpal bone, distal to lunate (L) and proximal to third metacarpal (3MC)
  • 37. Normal flexor retinaculum Flexor retinaculum is flat or convex Flexor retinaculum situated at level of line drawn between trapezium (TR) and hook of hamate (H) Absence of palmar bowing Transverse US of carpal tunnel at outlet Ng AWH et al. Clin Radiol 2018;73(2):214.e11–214.e18.
  • 38. Transverse ultrasound of Guyon’s canal Guyon canal contains ulnar artery (A), ulnar vein(V) & ulnar nerve (U) Cross-sectional images of the nerve show sites of its division into two branches: deep motor and superficial sensory branch Olchowy C et al. J Ultrason 2017;17:123–128.
  • 39. Anatomic variants of carpal tunnel • Median nerve: Proximal bifurcation (3% of the general population) Proximal trifurcation (extremely rare) • Persistent median artery: 3% of the general population • Intrusion of flexor digitorum superficialis into carpal tunnel • Reversed palmaris longus • Accessory muscles Presazzi A et al. J Ultrasound 2011;14:40–46. Numerous variants involving nerves, artery, tendons and muscles
  • 40. Proximal bifurcation of median nerve CTS: carpal tunnel syndrome – CSA: criss-sectional area Peer S et al. Imaging Med 2012;4(3):287–297. Bifid median nerve (arrows) & hyperechoic epineurium (arrowheads) Diameters of 2 nerves vary considerably: generally they of same size Might predispose to carpal tunnel syndrome Transverse US of carpal tunnel in a healthy volunteer
  • 41. Proximal trifurcation of median nerve rare anatomic variant Median nerve divided into three branches Three nerves travelling in carpal tunnel just below the flexor retinaculum (arrows) Transverse US of carpal tunnel Presazzi A et al. J Ultrasound 2011;14:40–46.
  • 42. Persistent median artery Prevalence 3% – Might predispose to carpal tunnel syndrome Normal median nerve with eccentric PMA (37%) High division of median nerve with midline PMA (44%) Bifid median nerve with midline PMA (19%) PMA: persistent median artery Gassner EM et al. J Ultrasound Med 2002;21:455–461.
  • 43. Persistent median artery and veins Left image: bifid median nerve, persistent median A & V (arrowheads) Right image: collapsed veins with light probe compression Small image: color Doppler of artery and veins Ekiz T et al. Am J Phys Med Rehabil 2016; Transverse US of carpal tunnel in a healthy man
  • 44. Reversed palmaris longus Presazzi A et al. J Ultrasound 2011;14:40–46. Tendon in proximal position Muscle belly in distal position May cause carpal tunnel syndrome Reversed palmaris longus Transverse US of carpal tunnel Normal palmaris longus Anatomic drawing Muscle belly in proximal position Tendon in distal position
  • 45. Muscle belly of flexor digitorum superficialis in carpal tunnel Presazzi A et al. J Ultrasound 2011;14:40–46. Transverse US of carpal tunnel in a healthy man Muscle belly of flexor digitorum superficialis in carpal tunnel Normally only flexor digitorum tendons travel in carpal tunnel This variant can cause carpal tunnel syndrome
  • 46. ③ Ultrasound features of carpal tunnel syndrome
  • 47. Indications of US in carpal tunnel syndrome • Complementary to electrodiagnostic testing for diagnosis Equally suited for diagnosis as electrodiagnostic testing • Diagnosis of space occupying lesions in carpal tunnel syndrome • Poor outcome after carpal tunnel release Peer S et al. Imaging Med 2012;4(3):287–297.
  • 48. • Patient comfortably seated across from examiner • Wrist on table at comfortable height in slight extension (10-20) • Generous gel throughout distal arm to wrist • Staying perpendicular to structure • Areas examined: - Distal forearm: pronator quadratus - Carpal tunnel: inlet, tunnel, outlet • Dynamic tests US protocol for carpal tunnel syndrome
  • 49. US protocol for carpal tunnel syndrome ① Transverse US of distal forearm: CSA of median nerve ② Transverse US of carpal tunnel inlet: CSA of median nerve ③ Transverse US from tunnel to outlet: space occupying lesions ④ Longitudinal US of carpal tunnel: deformation of median nerve ⑤ Dynamic tests: thenar flexion stress test, muscle intrusion tests CSA: cross-sectional area Chen YT et al. J Ultrasound Med 2016;35:e11–e24. With practice, this protocol evaluates carpal tunnel in < 90 sec Areas to examine
  • 50. Ultrasound features of carpal tunnel syndrome • CSA of median nerve at maximum swelling: ≥ 10 mm2 • Wrist-to-forearm ratio of median nerve CSA : ≥ 1.4 • Inlet-to-outlet ratio of median nerve CSA: ≥ 1.3 • Intraneural vascularity of median nerve on Doppler Peer S et al. Imaging Med 2012;4(3):287–297. Commonly evaluated features • Longitudinal compression of median nerve • Increased flattening ratio of median nerve at pisiform/hamate level • Loss of fascicular discrimination of medial nerve • Thickened outer epineurium of median nerve • Bowing of flexor retinaculum: ≥ 0.14 • Thickening of flexor retinaculum Other evaluated features
  • 51. Cross-sectional area of median nerve Normal: 7 – 9.5 mm2 • Site: Level of maximum swelling of median nerve (preferred) Proximal edge of flexor retinaculum (carpal tunnel inlet) Level of pisiform bone • Method: Direct tracing around inner border of epineurium Accurate and reproducible Better than ellipsoid method (irregular median nerve) Chen YT et al. J Ultrasound Med 2016;35:e11–e24. Direct tracing of median nerve around inner border of epineurium at level of maximum swelling
  • 52. Cross-sectional area of median nerve Sagittal and transverse US of median nerve CSA: cross-sectional area Peer S et al. Imaging Med 2012;4(3):287–297. Median nerve compressed under thickened retinaculum (arrowheads) Area to measure CSA is proximal to upper edge of retinaculum (arrows) CSA: 23 mm2 (normal < 10 mm2)
  • 53. Cross-sectional area of median nerve at inlet > 10 mm2 is sensitive and specific for diagnosis of CTS CTS: carpal tunnel syndrome 1 Cartwright MS et al. Muscle Nerve 2012; 46:287–293. 2 Torres-Costoso A et al. Arch J Phys Med Rehabi 2018:99(4):758-765. Most validated ultrasound parameter As accurate as electrodiagnostic tests for diagnosis 1 Sensibility 81% & specificity 84% in a recent meta-analysis 2
  • 54. Wrist-to-forearm ratio of median nerve CSA CSA at tunnel inlet/CSA 12 cm proximally Level of pronator quadratus Transverse US of median nerve Level of tunnel inlet CSA: cross-sectional area – FCR: flexor carpi radialis Kapuścińska K et al. J Ultrasonography 2015;15:283–291. CSA of median nerve at pronator quadratus : 10 mm2 CSA of median nerve at tunnel inlet: 18 mm2 Wrist-to-forearm ratio: 1.8 (normal < 1.4)
  • 55. Inlet-to-outlet ratio of median nerve CSA CSA at tunnel inlet/CSA at tunnel outlet CSA: cross-sectional area – CTS: carpal tunnel syndrome Fu T et al. PLoS ONE 2015;10(1): e0116777. CSA of median nerve at tunnel inlet: 17 mm2 CSA of median nerve at tunnel outlet: 10 mm2 Inlet-to-outlet ratio: 1.7 (normal < 1.3) Carpet tunnel inlet Carpet tunnel outlet Transverse US of median nerve
  • 56. Intraneural vascularity of median nerve Systematic review: 7 studies – methodological shortcomings • Doppler techniques: color, power and spectral Power Doppler detects slow flow: best to detect intraneural flow • Intraneural blood flow not detected by Doppler in healthy subjects • Median sensitivity: 72% (range 41–95%) Median specificity: 88% (range 71– 100%) Good specificity interpreted with caution because of spectrum bias • Advantages of Doppler: better tolerated than electrodiagnostic study • Limitations of Doppler: operator dependent Vanderschueren GA et al. Muscle Nerve 2014;50:159–63.
  • 57. 67-year-old male with left carpal tunnel syndrome proven by nerve conduction studies & surgical findings Transverse & longitudinal color Doppler US of median nerve Hypervascularity of median nerve At least one vessel ˃ 1 mm in length in sagittal or axial plane Intraneural vascularity of median nerve Ooi CC et al. Skeletal Radiol 214;43(10):1387–94.
  • 58. In: Carpal tunnel syndrome and related median neuropathies. SFM Duncan & R Kakinoki (Eds), Springer International Publishing, 2017. Intraneural vascularity of median nerve Median nerve enlargement Intraneural vascularity on power Doppler (arrow) Transverse power Doppler US of carpal tunnel
  • 59. Intraneural vascularity of median nerve Joy V et al. J Neurol Sciences 2011;308:16–20. Particular value of Doppler in cases of negative nerve conduction studies Longitudinal US of median nerve at wrist Color and Doppler spectral analysis
  • 60. Longitudinal compression sign of median nerve Compression of median nerve as it passes under retinaculum C: Capitate – L: Lunate – R: Radius Peer S et al. Imaging Med 2012;4(3):287–297. Increased flattening of left median nerve (arrows) Longitudinal US of median nerve along carpal tunnel Normal tapering of right medial nerve inside carpal tunnel (arrow) Left median nerve Right median nerve
  • 61. Flatening ratio of media nerve Ratio between the largest & smallest diameters of the nerve CTS: carpal tunnel syndrome Mani B et al. J Med Imag Rad Oncol 2011;55:126–131. Largest diameter: 6.3 mm – Smallest diameter: 1.9 mm Flattening ration of median nerve: 3.16 Normal value: 2.55 ± 0.54 at mid carpal tunnel Overlaps with values in carpal tunnel syndrome patients Largest diameter Smallest diameter
  • 62. Loss of fascicular discrimination of medial nerve Patient with severe carpal tunnel syndrome Transverse US of median nerve Peer S et al. Imaging Med 2012;4(3):287–297. Loss of fascicular discrimination CSA of median nerve at proximal edge of retinaculum: 54 mm2
  • 63. Thickened outer epineurium of median nerve Median nerve massively swollen Thickened echoic outer epineurium (arrowheads) Peer S et al. Imaging Med 2012;4(3):287–297. Patient with longstanding severe carpal tunnel syndrome Transverse ultrasound of carpal tunnel
  • 64. Flexor retinaculum bowing ratio Transverse US of carpal tunnel at outlet Distance of palmar displacement (arrow) Divided by distance between trapezium & hook of hamate (line) f: flexor tendons – h: hook of hamate – t: trapezium Normal ratio: 0 to 0.15 – Ratio in CTS: 0.14 to 0.26 Altinok T et al. Surg Radiol Anat 2004;26:501–503. In: Carpal tunnel syndrome and related median neuropathies. SFM Duncan & R Kakinoki (Eds), Springer International Publishing, 2017.
  • 65. Thickening of flexor retinaculum FR: flexor retinaculum In: Carpal tunnel syndrome and related median neuropathies. SFM Duncan & R Kakinoki (Eds), Springer International Publishing, 2017. Transverse US of carpal tunnel inlet Thickening of FR (arrow) Enlarged median nerve (arrowhead Enlarged median nerve Cross-sectional area: 22.9 mm2
  • 66. Dynamic US tests of carpal tunnel syndrome
  • 67. Dynamic US tests of carpal tunnel syndrome Chen YT et al. J Ultrasound Med 2016;35:e11–e24. • Thenar flexion stress test: transverse & longitudinal view Dynamic changes of median nerve caliber • Flexor digitorum superficialis intrusion test: transverse view Intrusion of flexor digitorum superficialis into carpal tunnel • Lumbrical intrusion test: transverse view Intrusion of lumbricals into carpal tunnel
  • 68. Thenar digital flexion stress test Chen YT et al. J Ultrasound Med 2016;35:e11–e24. An object is placed in the hand of the patient Patient apply gentle squeeze between thumb, index & middle finger Transducer over median nerve in long axis Transducer over carpal tunnel in transverse axis
  • 69. Thenar digital flexion stress test Relaxed view Stressed view Longitudinal US of median nerve along carpal tunnel Thenar muscle bulging into MN Diameter of median nerve 0.7 mm Median nerve diameter: 2 mm Takata SC et al. J Diagn Med Sonogr 2019;35(1):62–68.
  • 70. Thenar digital flexion stress test Transverse US of carpal tunnel Stressed viewRelaxed view Thickness of median nerve decreases from 2.2 mm to 1.4 mm (0.14 cm) during stress 36% “flattening” compression Takata SC et al. J Diagn Med Sonogr 2019;35(1):62–68.
  • 71. Flexor digitorum superficialis intrusion test Aboul-fotouh M et al. Egyptian J Radiol Nuclear Med 2018;49:1060–1067. Combined wrist and digit extension
  • 72. Flexor digitorum superficialis intrusion test FDS: flexor digitorum superficialis Chen YT et al. J Ultrasound Med 2016;35:e11–e24. Wrist & fingers extension Flexor digitorum superficialis (*) enters carpal tunnel and appearing as hypoechoic mass Transverse US of carpal tunnel Normal carpal tunnel at rest Relaxed wrist & fingers median n median n FDS
  • 73. Chen YT et al. J Ultrasound Med 2016;35:e11–e24. Patient asked to make a fist Lumbricals are intrinsic muscles of hand that flex metacarpophalangeal joints & extend interphalangeal joints Lumbrical intrusion test
  • 74. Transverse US of carpal tunnel relaxed fingers Lumbrical intrusion test Chen YT et al. J Ultrasound Med 2016;35:e11–e24. Transverse US of carpal tunnel patient asked to make a fist Normal carpal tunnel at rest Hypoechoic lumbrical enters carpal tunnel and displacing median nerve
  • 75. Small portion of lumbrical muscle (white arrow) next to median nerve (asterisk) Takata SC et al. J Diagn Med Sonogr 2019;35(1):62–68. Lumbrical intrusion test Transverse US of carpal tunnel Relaxed fingers Transverse US of carpal tunnel Patient asked to make a fist Structure becomes enlarged along with additional muscles (white arrows)
  • 76. Ultrasound assessment of CTS severity Systematic review and meta-analysis • Mild carpal tunnel syndrome: Mean CSA of median nerve: 11.64 mm2 (95% CI: 11.23–12.05 mm2) • Moderate carpal tunnel syndrome: Mean CSA of median nerve: 13.74 mm2 (95% CI: 12.59–14.89 mm2) • Severe carpal tunnel syndrome: Mean CSA of median nerve: 16.80 mm2 (95% CI: 14.50–19.1 mm2) CSA: cross-sectional area – CTS: carpal tunnel syndrome Roomizadeh P et al. Am J Phys Med Rehabil 2019;98:373–381. Compared to electrodiagnostic classification of CTS severity
  • 77. Ultrasound can assess severity of CTS
  • 78. ④ US of space occupying lesions in carpal tunnel External compression of median nerve Rare cause of carpal tunnel syndrome: 2 – 3.5%
  • 79. Space occupying lesions & carpal tunnel syndrome • Tenosynovitis • Ganglion cyst • Bifid median nerve • Vascular anomalies: persistent median a. – thrombosed median a. • Tumors: hematoma – lipoma – neuroma • Rheumatoid arthritis: rheumatoid nodule • Gouty tophus • Calcified nodule • Accessory muscles Peer S et al. Imaging Med 2012;4(3):287–297. External compression of median nerve
  • 80. Tenosynovitis Peer S et al. Imaging Med 2012;4(3):287–297. Transverse ultrasound of carpal tunnel Patient with carpal tunnel syndrome Marked hypoechoic fluid collections (arrows) between mildly swollen flexor tendons diagnostic of tenosynovitis Flattened median nerve (arrowheads)
  • 81. Peer S et al. Imaging Med 2012;4(3):287–297. Ganglion cyst Patient with mild carpal tunnel syndrome Large eccentric space occupying ganglion cyst (arrowheads) abutting flexor tendons & dislocating median nerve (arrow) Transverse US of carpal tunnel
  • 82. Bifid median nerve Hypoechoic enlargement of median nerve trunks (arrows) proximal to carpal tunnel with transition to normal size within carpal tunnel (arrowheads) 79-year-old woman with carpal tunnel syndrome Jacobson JA et al. J Ultrasound Med 2016;35:683–693. Transverse US of carpal tunnel Sagittal US of median nerve
  • 83. Persistent median artery Deniel A et al. Diag Interv Imaging 2015;96:1261–1278. Persistent medial artery with bifid median nerve Cross- sectional of of 2 components: 12 mm2 Median artery situated between the two nerves Identification can be facilitated by color-Doppler examination Patient with carpal tunnel syndrome Transverse US of carpal tunnel Correspondent power Doppler US
  • 84. Peer S et al. Imaging Med 2012;4(3):287–297. Thrombosed median artery (arrow) between fascicles of bifid median nerve (arrowheads) Resection of artery resulted in improvement of symptoms Transverse ultrasound of carpal tunnel Thrombosed persistent median artery
  • 85. Bouton C et al. Presse Med 2016;45:707. Thrombosed persistent median artery Transverse color Doppler US of carpal tunnel Thrombosed median artery (A) in the middle of bifid median nerve (N)
  • 86. Intraneural hematoma of median nerve Median nerve with intraneural hematoma Transverse US of carpal tunnel Intraoperative photograph Longitudinal US of median nerve Intraneural hematoma (arrows) Intraneural hematoma (arrows) Unterholzner V et al. Ultraschall Med 2012 Nov 5. DOI: 10.1055/s-0032-1325459. 66-year-old woman, acute CTS, no trauma or anticoagulant medication Takes pressure at left wrist up to 20 times/d by wrist-measuring device
  • 87. https://theultrasoundsite.co.uk/ultrasound-case-studies/lipoma-compressing-median-nerve-wrist/ Lipoma 50-year-old man, lump of right volar wrist, right hand paraesthesia Indentation of median nerveLipoma in carpal tunnel Transverse US of carpal tunnel Longitudinal US of median nerve
  • 88. Nerve sheath tumor Nerve sheath tumor of median nerve (yellow arrow) R: radius – L: lunate In: Carpal tunnel syndrome and related median neuropathies. SFM Duncan & R Kakinoki (Eds), Springer International Publishing, 2017. Patient with carpal tunnel syndrome Longitudinal and transverse US of carpal tunnel
  • 89. Nerve sheath tumor Patient with carpal tunnel syndrome Longitudinal and transverse US of carpal tunnel Oval-shaped homogenous hypoechoic tumor (arrows) arising from median nerve (dashed arrows)
  • 90. Rhumatoid nodule Patient with long-standing rheumatoid arthritis & unilateral CTS Transverse US of carpal tunnel Sagittal US of median nerve Hypoechoic nodule (open arrows) adjacent to and dislocating median nerve (dashed arrows)
  • 91. Gouty tophus Echogenic structures in radiocarpal joint in carpal tunnel floor (arrows) Marked flattening of median nerve at distal tunnel (*) Aggregates of pseudogout crystals at surgery Ooi CC et al. Skeletal Radiol 2014;43(10):1387–94. 62-year-old male, fullness in right wrist, numbness of first 3 digits Transverse US of carpal tunnel Sagittal US of carpal tunnel
  • 92. Calcified nodule in carpal tunnel Cheng TF et al. Frontiers Neurol 2019;10: article 224. Transverse US of carpal tunnel Sagittal US of carpal tunnel Hyperechoic ovoid lesion occupying the carpal tunnel with obvious median nerve compression Grayish calcified nodule on pathological findings
  • 93. Usefulness of US to rule out space occupying lesions in carpal tunnel is one of main reasons why we should perform it in every patient suspected of having CTS CTS: carpal tunnel syndrome Peer S et al. Imaging Med 2012;4(3):287–297.
  • 94. ⑤ Advanced technique: median nerve elastography
  • 95. Techniques of elastography World federation of ultrasound in medicine & biology • Strain elastography: Qualitative: results in color map Degree of strain converted into color map superimposed on US image • Aacoustic radiation force impulse (ARFI): Qualitative & quantitative Point shear wave elastography (pSWE): results in m/sec Two dimensions shear wave elastography (2D SWE): results in kPa kPa: kilopascal Ferraioli G et al. Ultrasound Med Biol 2018;44(12):2419–2440.
  • 96. Strain elastography of median nerve In: Carpal tunnel syndrome and related median neuropathies. SFM Duncan & R Kakinoki (Eds), Springer International Publishing, 2017. Healthy volunteer Normal size median nerve (yellow arrowhead) Color mapping on elastography indicating soft nerve (red)
  • 97. Enlarged median nerve (yellow arrowhead) Color mapping on elastography indicating stiff nerve (blue) Strain elastography of median nerve In: Carpal tunnel syndrome and related median neuropathies. SFM Duncan & R Kakinoki (Eds), Springer International Publishing, 2017. Patient with carpal tunnel syndrome
  • 98. 2D shear wave elastography of median nerve Kantarci F et al. Eur Radiol 2014;24:434–440. Color box in proximal carpal tunnel Yellow to red stiff flexor tendons – Non-stiff blue median nerve Region of interest for SWE measurement includes just the median nerve Mean elasticity of median nerve: 35.1 kPa Healthy volunteer Longitudinal US of median nerve along carpal tunnel
  • 99. 2D shear wave elastography of median nerve Kantarci F et al. Eur Radiol 2014;24:434–440. Patient with moderate carpal tunnel syndrome Longitudinal US of median nerve along carpal tunnel Mean elasticity of median nerve: 54.3 kPa R: distal radius – C: proximal carpal row (lunate)
  • 100. 2D shear wave elastography of median nerve Kantarci F et al. Eur Radiol 2014;24:434–440. Patient with severe carpal tunnel syndrome Longitudinal US of median nerve along carpal tunnel Mean elasticity of median nerve: 130.9 kPa R: distal radius – C: lunate
  • 101. • 17 studies: 820 wrists with CTS and 581 asymptomatic wrists Strain elastography: 13 studies – 2D SWE (4 studies) • Median nerve at wrist stiffer in CTS than those in healthy controls • Shear wave elastography more sensitive than strain elastography to discriminate between patients with CTS and those without • Ultrasound elastography revealed its potential in differentiating CTS of different severity Elastography of medial nerve in CTS Systematic review and meta-analysis CTS: carpal tunnel syndrome – 2D SWE: two dimensions shear wave elastography Lin CP et al. Ultrasound Med Biol 2019 Aug 9. doi: 10.1016/j.ultrasmedbio.2019.07.409.
  • 102. ⑥ Ultrasound after carpal tunnel release
  • 103. Poor outcome after carpal tunnel release Causes of unfavorable outcome • Extension of flexor digitorum muscle bellies into carpal tunnel • Incomplete dissection of flexor retinaculum • Hematoma • Soft tissue infection • Scar formation • Traumatic neuroma Peer S et al. Imaging Med 2012;4(3):287–297.
  • 104. Flexor digitorum muscle bellies in carpal tunnel Castillo R et al. Arch plastic Surg 2018;45(5):474–478. Aberrant distal extension of flexor digitorum muscle belly into carpal tunnel which can result in crowding of carpal tunnel & recurrence of symptoms of carpal tunnel
  • 105. Castillo R et al. Arch plastic Surg 2018;45(5):474–478. Flexor digitorum muscle bellies in carpal tunnel Extension of second flexor muscle belly (arrow) into carpal tunnel in proximity to median nerve (asterisk) Recurrent carpal tunnel syndrome 20 years after release Longitudinal & transverse US of carpal tunnel
  • 106. Incomplete dissection of flexor retinaculum Tan TC et al. Hand Surgery 2011;16(3):289–294. Patient with poor outcome after carpal tunnel release Longitudinal ultrasound of median nerve Indentation onto the median nerve
  • 107. Peer S et al. Imaging Med 2012;4(3):287–297. Soft-tissue infection Hypertrophic inflamed subcutaneous tissue (arrows) invading the median nerve (arrowheads) Patient with poor outcome after carpal tunnel release Transverse US of carpal tunnel
  • 108. Patient with poor outcome after carpal tunnel release Transverse US of carpal tunnel Peer S et al. Imaging Med 2012;4(3):287–297. Compression of median nerve (arrowheads) by hypertrophic scar formation (arrows) Hypertrophic scar
  • 109. Enlarged median nerve (arrowhead) Surrounding scar tissue (arrow) In: Carpal tunnel syndrome and related median neuropathies. SFM Duncan & R Kakinoki (Eds), Springer International Publishing, 2017. Hypertrophic scar Patient with poor outcome after carpal tunnel release Transverse US of carpal tunnel Asymptomatic right wristSymptomatic left wrist Normal median nerve (arrowhead
  • 110. Traumatic neuroma Normal appearance of posterior fascicles (arrows) Hypoechoic post-traumatic neuroma of anterior part of nerve (N) In-continuity neuroma of median nerve Patient with poor outcome after carpal tunnel release Transverse US of carpal tunnel Depaoli R et al. J Ultrasound 2015;18:83–85.
  • 111. Traumatic neuroma Patient with poor outcome after carpal tunnel release Longitudinal and transverse US of median nerve Focal hypoechoic swollen region Continuous proximally & distally with normal median nerve Located 2–3 cm proximal to wrist crease Cross-sectional area: 20.3 mm2 N: nerve Chen KH et al. Am J Phys Med Rehabil 2009;88;771–774.
  • 112. Sonography should be performed in every patient with poor outcome after surgery or conservative treatment
  • 113. Conclusion • State-of-the-art machine, high frequency transducer & good operator experience are prerequisites for ultrasound in CTS • US is cheap, noninvasive, accurate and reproducible imaging modality for the diagnosis of CTS and its severity • Space occupying lesions of carpal tunnel is one of the main reasons to perform ultrasound in every patient with CTS • Ultrasound elastography can assess severity of CTS • Ultrasound is useful in poor outcome after carpal tunnel release CTS: carpal tunnel syndrome
  • 115. • Sensibility: 81% (95% CI: 74–88) • Specificity: 84% (95% CI: 78–90) • Positive likelihood ratio: 6.22 (95% CI: 3.99–9.71) • Negative likelihood ratio: 0.16 (95% CI: 0.11–0.26) • Diagnostic odds ratio: 31.11 (95% CI: 20.42–47.40) CSA of median nerve in carpal tunnel syndrome Most commonly evaluated parameter CSA: cross-sectional area Torres-Costoso A et al. Arch Phys Med Rehabi 2018;99(4):758–765. Diagnostic accuracy of CSA at inlet from 9 to 12.5 mm2 Systematic review and meta-analysis