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644 AJR:193, September 2009

Materials and Methods

Our institutional review board approved this

study, and oral inormed consent was obtained

rom all patients.

Patient Sample

We perormed a retrospective study o 47 wrists

o 47 patients (11 men, 36 women; mean age, 55

years; range, 27–81 years) consecutively reerred

or MRI by an orthopedic surgeon at our institu-

tion. Because they had upper extremity symptoms

ater open surgical release o the median nerve,

the 47 patients had been consecutively reerred to

and reexamined by the orthopedic surgeon or

electrophysiologic evidence o CTS. The previous

surgical release had been perormed by several or-

thopedic surgeons at other institutions. No patientreceived steroid injections or other treatments to

manage chronic pain syndromes beore the MRI

examination. During reexaminations, nerve con-

duction studies and needle EMG were used to de-

termine the presence or absence o recurrent CTS

ater surgery.

Thirty-ve patients had EMG evidence o recur-

rent CTS. The 12 patients without EMG evidence

o recurrent CTS were the control group. The con-

trol group was not a truly disease-ree group. The

MRI Assessment of Recurrent

Carpal Tunnel Syndrome AfterOpen Surgical Release of theMedian Nerve

Raphaël Campagna1

Eric Pessis1

Antoine Feydy1

Henri Guerini1

Dominique Le Viet2

Patrick Corlobé2

Jean-Luc Drapé1

Campagna R, Pessis E, Feydy A, et al.

1

Université Paris Descartes, Assistance Publique-Hôpitaux de Paris, Service de Radiologie B, Hôpital

Cochin, 27 rue du Faubourg Saint Jacques, 75679 Paris

Cedex 14, France. Address correspondence to

R. Campagna ([email protected]).

2Institut de la Main, Paris, France.

Musculoskeleta l Imaging • Orig ina l Research

AJR 2009; 193:644–650

0361–803X/09/1933–644

© American Roentgen Ray Society

The diagnosis o carpal tunnel syn-

drome (CTS) relies on clinical

eatures and electrophysiologic

data. Although imaging o the

median nerve in the carpal tunnel has received

attention in the literature, the technique has

limited value in the diagnosis o CTS in daily

practice [1, 2]. Surgical release o the median

nerve is requently needed when conservative

treatment has ailed. However, ater surgical

release, some patients continue to have symp-

toms. Because ailure o nerve decompression

has numerous causes [3–7], including teno-

synovitis o fexor tendons, nerve section, -

brosis, extrinsic nerve compression, nerve en-

trapment, and bone racture, these patients

pose a challenging clinical problem. In addi-tion, the occurrence o subjective pain ater

surgery is well known [8], and objective evi-

dence o nerve dysunction must be present

or urther surgical exploration. Imaging can

be helpul in the postoperative care o these

patients. We aimed to determine with MRI

the morphologic eatures o the median nerve

in patients with electrophysiologic (electro-

myographic [EMG]) evidence o recurrent

CTS ater surgical release.

Keywords: carpal tunnel, electromyography, MRI, wrist

DOI:10.2214/AJR.08.1433

Received June 24, 2008 ; accepted ater revision

February 3, 2009.

F O C U S O N :

OBJECTIVE. The purpose o this study was to retrospectively determine the accuracy o

MRI in identication o the morphologic eatures o median nerve dysunction ater surgical

release o the median nerve or carpal tunnel syndrome.

MATERIALS AND METHODS. Two blinded readers independently evaluated axial

1.5-T MR images or retinacular regrowth, morphologic characteristics o the median nerve,

and presence o mass eect, brosis, and carpal tunnel decompression. All 47 patients (11

men, 36 women; mean age, 55 years; range, 27–81 years) had undergone open surgical releaseo the median nerve or carpal tunnel syndrome. Thirty-ve patients had electromyographic

evidence o recurrent carpal tunnel syndrome. The other 12 patients did not have electrophys-

iologic evidence o recurrent carpal tunnel syndrome and were the control group.

RESULTS. A statistically signicant dierence between the recurrent carpal tunnel syn-

drome and control groups was ound or brosis ( p = 0.009), nerve enhancement ( p = 0.04),

and median nerve width ( p = 0.008) and ratio ( p = 0.01) at the pisiorm level.

CONCLUSION. MRI may be used in association with electromyography or accurate

postoperative evaluation o the carpal tunnel.

Campagna et al.MRI o Carpal Tunnel Syndrome

Musculoskeletal ImagingOriginal Research



AJR:193, September 2009 645

MRI of Carpal Tunnel Syndrome

patients had undergone MRI because o clinical

and electrophysiologic suspicion o ulnar nerve en-

trapment in Guyon’s tunnel (n = 1), clinical suspi-

cion o tenosynovitis (n = 3), and discrepancy be-

tween normal EMG results and clinical examination

ndings (loss o grip strength, scar discomort) (n =

8). To eliminate alse-positive results, we excluded

patients who had undergone EMG or MRI within 6

months ater surgery [9].

Imaging

MRI was perormed with a 1.5-T MRI unit

(Signa Excite, GE Healthcare) with a dedicated

quadrature wrist coil. All patients were placed in

the MR imager in the prone position with the el-

bow extended overhead and the pronated hand in

the center o the coil. The pulse sequences were an

axial spin-echo T1-weighted sequence (TR/TE,

400/14; section thickness, 4 mm; eld o view, 6

cm; acquisition time, 4 minutes 21 seconds; num-

ber o signals acquired, 4; matrix size, 256 × 160;

gap, 0.4 mm), an axial ast spin-echo STIR se-

quence (2,320/14; inversion time, 150 millisec-

onds; echo-train length, 9; section thickness, 4

mm; eld o view, 6 cm; acquisition time, 3 min-

utes 36 seconds; number o signals acquired, 4;

matrix size, 256 × 160; gap, 0.4 mm), and an axial

ast spin-echo T1-weighted sequence with at sup-

pression ater IV injection o 0.1 mmol/kg o body

weight o gadoterate dimeglumine (Dotarem,

Guerbet) (600/15; echo-train length, 3; section

thickness, 4 mm; eld o view, 6 cm; acquisition

time, 4 minutes 24 seconds; number o signals ac-

quired, 4; matrix, 256 × 160; gap, 0.4 mm). The

mean time between surgery and MRI was 28months (range, 6–193 months), and the mean time

between MRI and electrophysiologic testing was 3

months (range, 0–24 months).

Electrophysiologic Tests

Electrophysiologic studies included needle EMG

and routine motor and sensory nerve conduction

studies. All studies were perormed by the same

electrophysiologist beore MRI. The needle elec-

trode was connected to an EMG system (Viking,

Nicolet). The 12 patients in the control group had

normal results o EMG and nerve conduction stud-

ies with the ollowing data: no spontaneous muscu-

lar activity, distal motor latency less than 4.4 milli-seconds, sensitive conduction velocity greater than

44 m/s, and Kimura centimetric value less than 0.2

ms/cm. Patients with at least one abnormal EMG or

nerve conduction result were included in the recur-

rent CTS group (n = 35) according to previous de-

scriptions [10–13]. Results can vary over the time

owing to environmental and technical actors [14].

In our study, however, all tests were perormed by

the same electrophysiologist, and the temperature

o the room and the skin was monitored. All electro-

physiologic studies were perormed at least 6

months ater surgery.

Image Analysis

Two musculoskeletal radiologists (4 and 15

years o experience) blinded to electrophysiologic

results reviewed the images independently and

retrospectively at random using a PACS worksta-

tion (Carestream, Kodak). Discrepancies were re-

solved by consensus.

According to previous MRI descriptions o the

preoperative ndings o CTS and known operative

complications [3, 6, 15–19], the ollowing ndings

were reviewed. First, regrowth o the fexor reti-

naculum was dened as a continuous, linear area

o low signal intensity supercial to the nerve and

thickened in the area deep in relation to the subcu-

taneous scar (Figs. 1 and 2). Regrowth included

incomplete resection o the retinaculum, the pres-

ence o scar tissue that mimicked retinaculum,

and true regrowth o the retinaculum.

Second, median nerve analysis included the

presence o high signal intensity on ast STIR im-

ages in comparison with thenar muscle signal in-

tensity (Fig. 3). Median nerve measurements were

obtained with an electronic caliper at the proximal

(pisiorm) and distal (hook o the hamate) levels.

The cross-sectional area and ratio o width to

height (fattening ratio) were measured in milli-

meters at the two levels (Figs. 4 and 5). Nerve en-

hancement ater IV gadolinium injection was con-

sidered high i stronger than thenar muscle

enhancement (Fig. 6B). The shortest distance be-

tween the skin and the volar margin o the mediannerve was measured on axial images with an elec-

tronic caliper at the distal level (Fig. 7).

Third, analysis o mass eect in the carpal tun-

nel included the presence o bursitis (ocal fuid

collection > 1 cm in the carpal tunnel), a mass, ac-

cessory muscles or distal progression o the mus-

cle belly, bone racture or ragment, or fexor ten-

don tenosynovitis (excessive fuid within the

tendon sheath with gadolinium enhancement).

Fourth, the presence o brosis was dened by an

extensive area o low signal intensity with an ill-

dened nerve margin on T1-weighted images

(Figs. 6 and 8). Fith, to assess the quality o car-

pal tunnel decompression, we determined the po-

sition o the median nerve and leading fexor ten-

don. This position was compared with the line

joining the hook o the hamate to the ridge o the

trapezium, according to previous ndings [20].

Carpal release was considered successul i the

tendon or nerve was located above the line and i

no tendon or nerve was entirely located under this

line (Fig. 9). In the other cases, carpal tunnel re-

lease was considered insucient (Fig. 10).

Statistical Analysis

Quantitative variables were reported with the

mean and range (minimum to maximum). Cate-

goric variables were reported as count (percent-

age). Statistical analysis was perormed with a

nonparametric test (Mann-Whitney) or quantita-

tive variables and Fisher’s test or categoric vari-

ables. All tests were two sided. A value o p < 0.05

was considered signicant. Interrater agreement

was calculated or MRI ndings (kappa). All anal-

yses were perormed with statistical sotware

(MedCalc version 8.0, MedCalc Sotware).

Results

The sensitivity, specicity, and positive

and negative predictive values o MRI signs

are summarized in Table 1. The comparisons

o MRI signs or both groups are summa-rized in Tables 2 and 3. The ndings in the

recurrent CTS and control groups diered

statistically only or presence o brosis,

nerve enhancement, volar migration o nerve

and tendon (carpal decompression), and me-

dian nerve width and ratio at the pisiorm

level. For the ollowing items, there were no

TABLE 1: Sensitivity, Specificity, and Predictive Values of MRI Signs inDiagnosis of Recurrent Carpal Tunnel Syndrome

SignSensitivity

(%)Specicity

(%)Positive Predictive

Value (%)Negative Predictive

Value (%)

Retinacular regrowth 43 50 71 23Carpal tunnel mass eect 26 58 64 21

Fibrosis 60 83 92 42

Median nerve enhancement 40 92 94 34

Median nerve high signal intensity 74 33 77 31

Carpal tunnel decompression

Good 20 50 54 18

Insucient 80 50 82 46




Campagna et al.

statistically signicant dierences between

groups: regrowth o the fexor retinaculum;

cross-section area o the median nerve, nerve

ast STIR signal intensity, shortest distance

between skin and volar margin o the nerve,

and nerve measurement at the hamate level;

and mass eect in the carpal tunnel. Therewas no statistical dierence between groups

in time between surgery and MRI or between

surgery and EMG ( p > 0.05). According to

criteria commonly used or interpretation o

values [21], interobserver agreement or all

observed eatures was nearly perect, sub-

stantial, or moderate, except or direct visu-

alization o retinacular regrowth, which had

air agreement (Table 2).

Fig. 1—56-year-old woman with recurrent carpal tunnel syndrome and retinacularregrowth ater surgery. Axial T1-weighted spin-echo MR image (TR/ TE, 40 0/14)shows retinaculum as stripe o low signal intensity tightened rom hook o hamate

to ridge o trapezium (arrows ).

Fig. 2—61-year-old woman without electrophysiologic evidence o recurrentcarpal tunnel syndrome (control group) and retinacular section without regrowthater surgery. Axial T1-weighted spin-echo MR image (TR/ TE, 40 0/14) showsdiscontinuous stripe o low signal intensity. Arrows indicate persistent gap oretinaculum.

Fig. 3—46-year-old man with recurrent carpel tunnel syndrome. Axial T2-weighted STIR MR image (TR/TE, 2,320/14; inversion time, 150 milliseconds)shows high signal intensity o median nerve (asterisk ) relative to hypothenarmuscle signal intensity (arrowhead ). Arrows indicate site o retinacular regrowth.

Fig. 4—54-year-old woman without electrophysiologic evidence o recurrentcarpal tunnel syndrome (control group). Axial T1-weighted spin-echo MR image(TR/TE, 400/14) shows median nerve measurement at pisiorm level calculatedwith electronic caliper. Median nerve ratio is low (2.63/2.87 = 0.92).

Fig. 5—63-year-old manwith recurrent carpal

tunnel syndrome. AxialT1-weighted spin-echoMR image (TR/T E, 550/19)shows median nervemeasurement at pisiormlevel calculated withelectronic caliper. Medianwidth and nerve ratiois high (5.41/2.24 = 2.4).Flattened appearance onerve is evident.





Discussion

Our study showed that MRI is useul or

detecting signs o nerve dysunction: gado-

linium-enhanced areas, brosis, abnormal

nerve width and ratio, and insucient carpal

release. It also showed that MRI depicts signs

o nerve dysunction but cannot replace

electrophysiologic tests. MRI can be per-

ormed in association with EMG or patients

with pain ater carpal tunnel release.

Complications o carpal tunnel release oc-

cur in 3–19% o cases in large series and ne-

cessitates reexploration o the area or vari-

ous reasons in as many as 12% o cases [22].

In a previous meta-analysis [23], endoscopic

carpal tunnel release was comparable with

open release in rate o irreversible nerve

damage. Consequently, there likely was no

bias in our study sample, all o the patients

having undergone open surgical release. The

rate o recurrence o CTS ranges rom 1% to

25% [7]. The common causes o recurrent

CTS ater surgery are incomplete resection

or regrowth o the fexor retinaculum, brous

prolieration, fexor tenosynovitis, and ex-trinsic median nerve compression (accessory

muscle belly, cyst) [3–7]. We did not analyze

the ailure rate o carpal tunnel surgery be-

cause only patients who underwent postop-

erative EMG and MRI were included.

Physical examination o patients who have

undergone carpal tunnel surgery is especial-

ly dicult because o subjective pain and

scar discomort, which are requent ater

CTS surgery [8] and must be dierentiated

rom actual persistent median nerve injury.

We chose our patients only on the basis o

objective results o electrophysiologic tests,

although EMG results sometimes are abnor-

mal or several months. In our study, howev-

er, the mean time between surgery and EMG

was more than 2 years, probably reducing

the number o alse-positive cases.

To the best o our knowledge, this report is

the rst to describe MRI evidence o postop-

erative changes ater systematic IV gadolini-

um injection with a control group. In one

study [24], investigators compared postoper-

ative MRI eatures in patients with recurrent

CTS with those in controls but without gado-

linium injection. Another set o authors [25]

used gadolinium-enhanced MRI to evaluate

recurrent CTS but in only three patients.

Direct visualization o retinacular regrowth

had only air agreement and cannot be used to

assess carpal tunnel decompression. The oth-

er MRI eatures described had acceptable

interobserver agreement and thereore may be

used to assess decompression.

In our study, nerve enhancement was sta-

tistically correlated with recurrent CTS. The

cause o this enhancement remains unclear.

The nerve enhancement we observed might

have been the result o persistent nerve ede-

ma [26, 27] or partial nerve injury, as usually

is ound with posttraumatic neuroma [28].

A

Fig. 6—53-year-old woman with recurrent carpal tunnel syndrome and supercial brosis o carpal tunnel.A, Axial T1-weighted spin-echo MR image (TR/TE, 400/14) shows ill-dened area o low signal intensity ( asterisk ) between palmaris longus tendon (arrowhead ) and volaraspect o median nerve (arrow ). Loss o shape o volar margin o median nerve is eviden t.

B, Axial gadolinium-enhanced at-suppressed spin-echo T1-weighted MR image (400/14) shows strong enhancement o ill-dened area o low signal intensity (asterisk ).Arrow indicates strong enhancement o median nerve in comparison with hypothenar muscle enhancement (arrowhead ).

B

Fig. 7—72-year-oldwoman with recurrentcarpal tunnel syndrome.Axial spin-echo T1-weighted MR image (TR/TE, 40 0/14) at hamatelevel (10.45 mm) showsshortest distance(arrow ) between skinand volar margin omedian nerve.




Campagna et al.

Median nerve signal intensity has been

analyzed previously in patients who have un-

dergone surgery, and reduced median nerve

T2-weighted signal intensity has been ound

in patients with good clinical outcome [15,

17, 18, 29]. Our recurrent CTS group had

more median nerves with increased T2-

weighted signal intensity than did the control

group, as was ound previously [24]. This

dierence, however, was not signicant, and

the criteria or T2-weighted signal intensity

o the median nerve could not be used to di-

erentiate pathologic and healthy nerves ater

surgical release.

The cross-sectional area o the median nerve

at the pisiorm level has been described [10, 13]

as the most accurate criterion in the preopera-

tive diagnosis o CTS. We ound nerve height

and cross-sectional area at the pisiorm and

hamate levels to be not signicantly dierent

between the recurrent CTS and control groups.

These results suggest that these various mea-

surements have limited clinical utility in the

evaluation o postoperative CTS.

The median nerve width and fattening ra-

tio at the pisiorm level was higher in the re-

current CTS than in the control group, and

the dierence was statistically signicant.

This dierence has been previously reported

[24] and may be an indirect sign o persistent

nerve compression.

Because interobserver agreement was only

air or direct visualization o the retinacu-

A

Fig. 8—62-year-old woman with recurrent carpal tunnel syndrome and deep brosis o carpal tunnel.A, Axial spin-echo T1-weighted MR image (TR/TE, 400/14) shows area o low signal intensity ( arrowheads ) on dorsal aspect o median nerve with mass eect ondisplaced fexor tendon (asterisks ).B, Gadolinium-enhanced at-suppressed axial T1-weighted spin-echo MR image (400/14) shows strong enhancement o ill-dened area (arrowheads ). Asterisk indicates

nerve enhancement.

B

Fig. 9—49-year-old man without electrophysiologic evidence o recurrent carpal tunnel syndrome (control group) and with leading fexor tendon and mediannerve position in carpal tunnel ater surgical release o nerve. Axial T1-weightedspin-echo MR image (TR/TE , 400/14) shows nerve (arrowhead ) and fexor tendon(asterisk ) above line joining hook o hamate to ridge o trapez ium. Carpal tunnelrelease was considered successul.

Fig. 10—67-year-old woman with recurrent carpal tunnel syndrome and leadingfexor tendon and median nerve position in postoperative carpal tunnel. AxialT1-weighted spin-echo MR image (TR/ TE, 55 0/19) shows nerve (arrowhead ) andfexor tendon (asterisk ) under line joining hook o hamate to ridge o trapez ium.Carpal tunnel release was considered insucient.





lum, we considered this eature not relevant

in the assessment o carpal tunnel decom-

pression. To quantitatively assess decom-

pression, we determined the position o the

median nerve and leading fexor tendon rela-

tive to the line joining the hook o the hamate

to the ridge o the trapezium, as described

previously [20]. Insucient carpal release

was more requent in the recurrent CTS

group than in the control group ( p = 0.04).

Although abnormal nerve and tendon migra-

tion is related to median nerve dysunction,

the sensitivity and specicity (50%) o this

MRI nding are too low and cannot be used

in daily practice.

We ound nine cases o mass eect, in-

cluding abnormal muscle belly, synovial

cysts, and tenosynovitis, as described previ-

ously [6, 15, 16, 19, 22, 30]. Abnormal mus-

cle belly and tenosynovitis were rare but

were seen in both groups. Synovial cyst was

seen only in the recurrent CTS group and is

a well-known cause o compression. The low

rate o mass eect may explain the absence

o a signicant dierence o this eature be-

tween the recurrent CTS and control groups.

Presence o median nerve brosis was a

relevant sign o recurrent CTS. We ound a60% rate o brosis in the recurrent CTS

group versus 17% in the control group. This

nding is consistent with ndings ater sur-

gical revision [22]. The detection o brosis

is helpul or planning surgical reinterven-

tion, and interposition o a composite grat

around the median nerve has been proposed

[31]. Two patterns o brosis were observed

in previous surgical studies [22, 32]: super-

cial extensive brosis between the palmaris

longus tendon and the volar aspect o the

nerve and deep brosis on the dorsal aspect

o the median nerve with mass eect on the

adjacent fexor tendon. In our study, deep -

brosis was seen only in the recurrent CTS

group (28%) and was more requent in our

study than in previous surgical observations

[22, 32]. These results suggest that deep -

brosis may be more requent than previously

expected [22, 32]. Supercial brosis was

ound more oten in the recurrent CTS group

(46% versus 17% in control group). This

nding is consistent with the results o a sur-

gical study [32] showing a 34% rate o super-

cial scar tethering.

The mean distance between the skin and

the volar aspect o the median nerve was thesame in our groups. Wu et al. [24] described

a more palmar location o the median nerve

in their recurrent CTS group but without a

signicant dierence rom controls.

Fibrosis can be detected and median nerve

measurements made without gadolinium in-

jection. In our experience, however, in di-

cult cases, injection o gadolinium was help-

ul or detecting brosis and measuring the

median nerve in the presence o brosis.

Moreover, nerve enhancement was statisti-

cally correlated with EMG dysunction. Thus

we believe that use o gadolinium injection

leads to more accurate diagnosis, especiallyin dicult cases, and helps surgeons in the

planning o reintervention.

Our study had several limitations. The

rst was the retrospective design and the

small number o patients with ull electro-

physiologic recovery ater surgical treatment

(control group). Further prospective studies

with a larger number o patients are needed

to conrm our results. Second, our patients

TABLE 3: Quantitative MRI Values in Wrists With Recurrent Carpal TunnelSyndrome and in Control Group

ValueRecurrent Carpal Tunnel

Syndrome (n = 35)Control(n = 12) p a

Mean distance between skin and volarmargin o median nerve (mm)

8.8 (4–20) 8.6 (6–11) 0.9

Median nerve width (mm) at level o

Pisiorm 6.17 5.04 0.008

Hook o hamate 5.94 5.21 0.08

Median nerve height (mm) at level o

Pisiorm 2.63 2.75 0.5

Hook o hamate 2.84 3.08 0.5

Median nerve surace (mm2) at level o

Pisiorm 12.90 10.88 0.1

Hook o hamate 13.16 12.04 0.7

Median nerve ratio at level o

Pisiorm 2.42 1.90 0.01

Hook o hamate 2.28 1.87 0.1

aNonparametric test (Mann-WhitneyU test).

TABLE 2: Prevalence of MRI Signs in Wrists With Recurrent Carpal TunnelSyndrome and Controls

Sign

Recurrent CarpalTunnel Syndrome

(n = 35)Control(n = 12) p a

InterobserverAgreement (κ)

Retinacular regrowth 15 (43) 6 (50) 0.6 0.3

Carpal tunnel mass eect 9 (26) 5 (42) 0.4Flexor tendons tenosynovitis 3 (8.6) 4 (33.3) 0.92

Synovial cyst 3 (8.6) 0 1

Accessory muscles 3 (8.6) 1 (8.3) 0.66

Fibrosis 21 (60) 2 (16.6) 0.009 0.67

Deep 10 (28) 0

Supercial 11 (31) 2 (16.6)

Median nerve enhancement 14 (40) 1 (8.3) 0.04 0.63

Median nerve high signal intensity 26 (74) 8 (66.7) 0.19 0.46

Carpel tunnel decompression 0.04 1

Good 7 (20) 6 (50)

Insucient 28 (80) 6 (50)

Note—Data are numbers with percentage in parentheses.aFisher’s test.

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