Carpal tunnel syndrome: diagnosis with high-resolution sonography.

OBJECTIVE. Carpal tunnel syndrome is characterized by typical anatomic changes that can be shown with high-resolution sonography. To determine whether these findings are reliable and can be used to establish the diagnosis, sonograms of patients with the disease were compared with sonograms obtained in patients with normal wrists. Also compared were sonograms and MR images obtained in the patients with carpal tunnel syndrome. SUBJECTS AND METHODS. Twenty wrists in 18 consecutive patients with clinical symptoms of carpal tunnel syndrome and with abnormal nerve conduction studies were examined with real-time sonography and MR imaging. The sonograms and MR images were evaluated quantitatively by two unbiased observers with regard to the size and shape of the median nerve and the palmar bowing of the flexor retinaculum. A t test was used to compare these data with those from previous sonographic studies of 28 normal wrists. Correlation coefficients for the measurements obtained with sonography and with MR were calculated. The relative accuracies of different diagnostic criteria for the diagnosis of carpal tunnel syndrome were assessed by using receiver-operating-characteristic analytical techniques. RESULTS. Characteristic findings on both MR and CT scans of the 20 wrists with carpal tunnel syndrome included swelling of the median nerve in the proximal part of the carpal tunnel in 16 wrists, flattening of the median nerve in the distal part of the carpal tunnel in 13 wrists, and increased palmar bowing of the flexor retinaculum in nine wrists. Comparison with the data of 28 normal wrists proved that these findings were significant (p less than .01 to p less than .001). Receiver-operating-characteristic analysis showed that the discrimination between wrists in normal subjects and in patients with carpal tunnel syndrome achieved with each of the three diagnostic criteria was not significantly different. Measurements of the size and flattening of the median nerve obtained from sonograms were similar to those on MR images, whereas sonography was less accurate for measuring the palmar bowing of the flexor retinaculum. CONCLUSION. We conclude that the results of sonography are reliable, and that the diagnosis of carpal tunnel syndrome can be established on the basis of sonographic findings.     

The role of ultrasonographic measurements of the median nerve in the diagnosis of carpal tunnel syndrome

AIM: The aim of study was to assess the usefulness of ultrasonographic measurements of the median nerve in the diagnosis of carpal tunnel syndrome. MATERIALS AND METHODS: Eighty-six patients with carpal tunnel syndrome confirmed by electromyography and 45 asymptomatic controls were included in the study and underwent high-resolution ultrasonography of the wrists. The cross-sectional area and flattening ratio at the level of the pisiform bone of the proximal carpal tunnel were measured. Data from the patient group and control group were compared to determine the statistical significance. The accuracy of the ultrasonographic diagnostic criteria for carpal tunnel syndrome was evaluated using receiver-operating characteristic (ROC) analysis. RESULTS: One hundred and forty-eight wrists of 86 patients with carpal tunnel syndrome and 76 wrists of 45 control patients were examined. All measurements showed significant differences between patients and controls. Increased cross-sectional area of the median nerve was the most predictive measurement of carpal tunnel syndrome. Using the ROC curve, a cut-off value of >10.5 mm2 at the level of pisiform bone provided a diagnostic sensitivity of 89% and specificity of 94.7% CONCLUSION: The ultrasonographic measurement of the median nerve cross-sectional area is a sensitive, specific and useful non-invasive method for the diagnosis of carpal tunnel syndrome.     

MR imaging of the carpal tunnel: normal anatomy and preliminary findings in the carpal tunnel syndrome

MR imaging was performed through the carpal tunnel in 18 wrists of nine normal volunteers and compared with cryomicrotome sections from cadaver wrists. MR reliably imaged the flexor retinaculum and carpal bones and thus defined the borders of the carpal tunnel. In all cases the median nerve was seen as an ovoid structure of moderate signal intensity and was easily distinguished from the flexor tendons of the hands running in the carpal tunnel. The tendons were separated from each other by their tendon sheaths, and this allowed for identification of the various tendons. Anatomic variations encountered in the normal volunteers included anomalous positioning of the origin of the lumbrical muscles within the carpal tunnel in two, persistent median arteries in two, and interposition of the median nerve between the flexor pollicis longus and the superficial flexor tendon to the index finger in one. Preliminary observations in 10 wrists of patients with carpal tunnel syndrome include segmental and diffuse swelling of the median nerve in six, distortion of the nerve in one, and thickening of the tendon sheaths in one. We conclude that MR imaging accurately and reliably displays the normal anatomy of the carpal tunnel and can detect morphologic changes in patients with carpal tunnel syndrome.     

Quantitative MR imaging of carpal tunnel syndrome.

OBJECTIVE: Previous MR imaging studies have produced evidence of changes to structures within the wrist believed to be associated with carpal tunnel syndrome. In an attempt to resolve the conflicting and inconclusive results of these studies, we report here the results of an MR imaging study at a field strength of 3.0 T, which is higher than that previously reported. SUBJECTS AND METHODS: Patients with carpal tunnel syndrome and control groups of asymptomatic subjects were studied using MR imaging. We evaluated electrophysiologically the median nerve function of the affected wrists of all patients. A gradient-recalled echo pulse sequence was used to study 13 3-mm-thick slices within the wrist of each patient or asymptomatic subject. Spatial resolution was approximately 0.3 x 0.3 mm2. The median nerve and other structures associated with the carpal tunnel, which were clearly shown on the MR images, were analyzed to yield structural data. RESULTS: Analysis revealed that the cross-sectional area of the nerve within and proximal to the carpal tunnel was approximately 50% larger in patients with carpal tunnel syndrome than in asymptomatic subjects. We found no significant difference in the area of the nerve within the carpal tunnel compartment compared with the area of the nerve proximal to the carpal tunnel either in patients or in asymptomatic subjects. Also, flattening of the nerve on entering the carpal tunnel was not significantly different in patients than in asymptomatic subjects. In patients an increase in the palmar bowing of the flexor retinaculum was found only at the level of the hamate compared with that found in asymptomatic subjects. The cross-sectional area of the carpal tunnel was of a similar size in patients and in asymptomatic subjects. Comparison of electrodiagnostic results indicated no correlations between the MR parameters and electrophysiologic dysfunction of the median nerve for patients. CONCLUSION: The only statistically significant differences found between patients with carpal tunnel syndrome and asymptomatic subjects were that the median nerve was approximately 50% larger within and proximal to the carpal tunnel in patients with carpal tunnel syndrome and palmar bowing of the flexor retinaculum occurred in patients only at the level of the hamate.     

Carpal tunnel syndrome caused by tophaceous gout: CT and MR imaging features in 20 patients

OBJECTIVE: The objective of this study is to describe the CT and MR imaging findings of gouty tophi in the wrist and present this entity as a cause of carpal tunnel syndrome. MATERIALS AND METHODS: Retrospective review of the CT (n = 18) and MR imaging (n = 20) studies of the wrist in patients with a documented diagnosis of gout who presented with gout-related carpal tunnel syndrome was performed; images of 24 wrists were collected over a 5-year period. Patient population included 20 men, who ranged in age from 35 to 76 years. All images were reviewed by two musculoskeletal radiologists who reached a consensus opinion. Surgical correlation was available in 12 patients. RESULTS: Tophi were found in the floor of the carpal tunnel (n = 18), carpal bones (n = 17), radiocarpal joint (n = 17), and extensor tendons or tendon sheaths (n = 16) of the wrist. All tophi showed similar signal characteristics (from low to intermediate signal intensity on T1-weighted images with heterogeneous signal intensity on T2-weighted images) with the exception of tophi in the floor of the carpal tunnel (low signal intensity on T2-weighted images). Varying degrees of calcification were noted on CT and MR imaging studies. Gadolinium-enhanced MR studies showed heterogeneous enhancement. CONCLUSION: Gouty tophi should be entertained as a cause of carpal tunnel syndrome in the appropriate patient population. Familiarity with this entity and its imaging characteristics may prove helpful in diagnosis and preoperative planning.     

CT study of the carpal tunnel. The carpal tunnel syndrome

The authors describe the CT aspects of carpal tunnel syndrome. Seventy-seven patients with signs and symptoms of carpal tunnel syndrome were studied, together with 28 postoperative controls (8 with and 20 without recurrence of symptoms) and 10 normal subjects. CT studies were carried out according to the conventional technique employing 3 high-definition axial slices respectively at the proximal end, in the middle and at the distal end of carpal tunnel. The patients affected with carpal tunnel syndrome presented changes in median nerve volume, in synovial sheet thickness, and in shape and density of the flexor tendons. Postoperative CT patterns of asymptomatic patients were similar to those of normal subjects. In the group of patients presenting postoperative recurrence of symptoms, 3 main findings were observed: incomplete surgery, newly formed cysts on the volar surface of the tunnel, and abnormal soft tissue interposed between the tendons. All the above findings were histologically confirmed during a second surgery. The authors believe CT to be a very useful tool in the evaluation of carpal tunnel syndrome, for both the first diagnosis and the demonstration of the causes of postoperative recurrences.     

MR imaging of the carpal tunnel syndrome

Magnetic resonance (MR) imaging of the carpal tunnel was performed in 23 wrists of 13 patients who were suspected to have carpal tunnel syndrome (CTS). In ten out of 23 wrists, diagnostic images of the carpal tunnel could be obtained. MR images were analysed retrospectively as to swelling of the median nerve, signal intensity of the median nerve on T2 weighted image, and swelling of the tendon sheath. In 8 wrists the median nerve was significantly swollen at the inlet of the carpal tunnel. Four of them showed increased signal intensity of the median nerve on T2 weighed image at the inlet. Swelling of the tendon sheath was demonstrated in two cases. These finding seem to represent edematous change of the median nerve due to compression. Surgical correlation was obtained in two wrists. Since MR imaging is capable of demonstrating pathological changes of the median nerve in CTS, it can be a diagnostic tool in selected cases.     

Dynamic MR imaging of carpal tunnel syndrome

 Objective. To evaluate the diagnostic value of the MR imaging syndrome before and after performance of provocative exercises in patients with dynamic carpal tunnel syndrome. Design. Fat-suppressed proton-density and T2-weighted spin-echo images of the wrist were obtained prior to and after provocative, standardized exercises. Images were interpreted in masked fashion with regard to six MR criteria of carpal tunnel syndrome: (a) bowing of the transverse ligament, (b) and (c) deformation of the median nerve at the pisiform and hamate levels respectively, (d) signal abnormality of the median nerve, (e) presence of fluid in the wrist joints and/or carpal tunnel, and (f) presence of synovial swelling. Patients. Twenty-one wrists in 20 patients with subjective complaints of carpal tunnel syndrome and equivocal or negative clinical findings and negative electrodiagnostic examinations were included (age range 21–61 years, mean 37 years, 2 men and 18 women). The diagnosis of dynamic carpal tunnel syndrome was made and confirmed by surgery in 18 of the 21 symptomatic wrists. The control group consisted of 15 asymptomatic wrists in volunteers (age range 22–60 years, mean 35 years, 8 men and 7 women). Results and conclusions. Sensitivities and specificities of the six MR criteria were 90.5–100%, and 6.7–86.7%, respectively, both before and after exercise. Likelihood ratios proved statistically significant differences between the symptomatic and asymptomatic wrists (P<0.0001–0.0002) for the prevalence of all MR criteria with the exception of fluid within the carpal joints and/or carpal tunnel. Changes of the MR appearance after exercise had a low sensitivity (4.8–71.4%) but high specificity (86.7–100%) for dynamic carpal tunnel syndrome. In conclusion, MR imaging contributes to the diagnosis of carpal tunnel syndrome when clinical signs are confusing and electrodiagnostic studies are negative. Dynamic examinations improve specificity of MR imaging for such diagnosis.     

Median nerve stiffness measurement by shear wave elastography: a potential sonographic method in the diagnosis of carpal tunnel syndrome

Objectives

To measure the median nerve (MN) stiffness by quantitative shear wave elastography (SWE) at the carpal tunnel inlet and to determine whether SWE can be used in the diagnosis of carpal tunnel syndrome (CTS).

Methods

The study included 37 consecutive patients (60 wrists) with a definitive diagnosis of CTS and 18 healthy volunteers (36 wrists). The MN cross-sectional area (CSA) by ultrasound and stiffness by SWE were studied. The difference between CTS patients and controls, and the difference among subgroups based on electrodiagnostic tests were studied by the Student’s t test. Interobserver variability and ROC analysis were performed.

Results

The MN stiffness was significantly higher in the CTS group (66.7 kPa) when compared to controls (32.0 kPa) (P?<?0.001), and higher in the severe or extreme severity group (101.4 kPa) than the mild or moderate severity group (55.1 kPa) (P?<?0.001). A 40.4-kPa cut-off value on SWE revealed sensitivity, specificity, PPV, NPV and accuracy of 93.3 %, 88.9 %, 93.3 %, 88.9 % and 91.7 %, respectively. Interobserver agreement was excellent for SWE measurements.

Conclusions

Median nerve stiffness at the carpal tunnel inlet is significantly higher in patients with carpal tunnel syndrome, for whom shear wave elastography appears to be a highly reproducible diagnostic technique.

Key Points

? Clinical examination is important for diagnosis of carpal tunnel syndrome ? Shear wave elastography (SWE) offers new clinical opportunities within diagnostic ultrasound ? SWE is highly reproducible in evaluation of median nerve stiffness ? Median nerve stiffness is significantly increased in carpal tunnel syndrome ? Elastography could become useful in diagnosis of carpal tunnel syndrome     

High resolution ultrasonography in the diagnosis of the carpal tunnel syndrome

PURPOSE: Carpal tunnel syndrome (CTS) is a neuropathy caused by compression of the median nerve in the carpal tunnel. Our purpose was to evaluate the role of high-resolution ultrasonography (US), performed with a 10-13 MHz probe, in the detection of morphovolumetric changes of the median nerve to confirm the clinical diagnosis. MATERIALS AND METHODS: Fifty healthy volunteers were examined first by US; subsequently we studied 294 wrists in 186 symptomatic patients, calculating the cross-sectional area of the median nerve at three levels: before the median nerve enters the carpal tunnel, at the carpal tunnel inlet and at the outlet. US was considered diagnostic for CTS when the median nerve area increased at the inlet or flattening was present along the carpal tunnel. RESULTS: Ultrasonography showed pathologic findings in 267 wrists: in 261 cases morphovolumetric changes of the median nerve were found; in six cases anatomic variant of the median nerve was detected. Surgery was performed in 277 cases and all patients became symptom-free. The sensitivity of US was 96.3 % . CONCLUSIONS: Our study confirms that quantitative ultrasonographic assessment is a useful support in confirming the clinical diagnosis of CTS.     

Sonography in the diagnosis of carpal tunnel syndrome.

OBJECTIVE: The few papers published on the use of sonography in carpal tunnel syndrome suggest it may be a useful diagnostic test. This study aims to prospectively evaluate the use of sonographic measurements of the median nerve in the diagnosis of carpal tunnel syndrome. SUBJECTS AND METHODS: Patients with documented carpal tunnel syndrome and a group of asymptomatic control subjects were enrolled and underwent high-resolution sonography of the carpal tunnel. A small-footprint linear array transducer was used to scan and measure the median nerve cross-sectional area and the maximum transverse and anteroposterior diameters. Data from the patient group and the control group were compared to establish optimal diagnostic criteria for carpal tunnel syndrome. RESULTS: Sixty-eight carpal tunnel syndrome patients (50 women, 18 men) with 102 affected nerves and 68 nerves in 36 asymptomatic controls (23 women, 13 men) were examined. Qualitative assessment alone was found to be unreliable. All measurements showed significant differences between patients and controls. The most predictive measurement was swelling of the median nerve, which was significantly greater in carpal tunnel syndrome patients compared with controls (mean, 0.13 cm2 versus 0.07 cm2). Thus, quantitative assessment of the median nerve provides an accurate diagnostic test (sensitivity, 82%; specificity, 97%), with an area larger than 0.09 cm2 being highly predictive of carpal tunnel syndrome. CONCLUSION: We confirm that median nerve cross-sectional area measurement correlates well with the presence of carpal tunnel syndrome and is both sensitive and specific for the diagnosis.     

Ultrasonography Findings of the Carpal Tunnel after Endoscopic Carpal Tunnel Release for Carpal Tunnel Syndrome

ObjectiveTo investigate changes in the median nerve, retinaculum, and carpal tunnel on ultrasound after successful endoscopic carpal tunnel release (ECTR).Materials and MethodsThis prospective study involved 37 wrists in 35 patients (5 male, 30 female; mean age ± standard deviation [SD], 56.9 ± 6.7 years) with primary carpal tunnel syndrome (CTS). An in-house developed scoring system (0–3) was used to gauge the clinical improvement after ECTR. Ultrasound was performed before ECTR, and at 1, 3, and 12 months post-ECTR. Changes in the median nerve, flexor retinaculum, and carpal tunnel morphology on ultrasound after ECTR were analyzed. Ultrasound parameters for different clinical improvement groups were compared.ResultsAll patients improved clinically after ECTR. The average clinical improvement score ± SD at 12 months post-ECTR was 2.2 ± 0.7. The median nerve cross-sectional area proximal and distal to the tunnel decreased at all time intervals post-ECTR but remained swollen compared to normal values. Serial changes in the median nerve caliber and retinacular bowing after ECTR were more pronounced at the tunnel outlet than at the tunnel inlet. The flexor retinaculum had reformed in 25 (68%) of 37 wrists after 12 months.ConclusionPostoperative changes in median nerve and retinaculum parameters were most pronounced at the tunnel outlet. Even in patients with clinical improvement after ECTR, nearly all ultrasound parameters remain abnormal at one year post-ECTR. These ultrasound parameters should not necessarily be relied upon to diagnose persistent CTS after ECTR.     

Gray scale and color Doppler sonography in the diagnosis of carpal tunnel syndrome

Purpose

To determine the diagnostic accuracy of gray scale and color Doppler sonography in the diagnosis of patients with carpal tunnel syndrome.

Patients and methods

A total of 53 wrists in 41 consecutive patients with clinical suspicion of carpal tunnel syndrome, referred from the Department of Physical medicine, Rheumatology & Rehabilitation were examined with ultrasonography using a 12 MHz linear array transducer. The presence of median nerve edema, swelling, and bowing of the flexor retinaculum was evaluated by gray scale sonography, while intraneural hypervascularity was evaluated by color Doppler sonography. Sensitivity and specificity were calculated for each sonographic feature and compared with electrodiagnostic test (EDT) results.

Results

Electrodiagnostic tests confirmed carpal tunnel syndrome in 48 wrists. A median nerve cross sectional area (CSA) of 11 mm² was calculated as a definition of median nerve swelling. In comparison with electrodiagnostic tests, median nerve swelling showed the highest accuracy (89%) among the gray scale sonographic criteria, and the presence of median nerve hypervascularization showed the highest accuracy (94%) among all sonographic criteria. Median nerve edema and bowing of the flexor retinaculum showed accuracies of 81% and 77% respectively.

Conclusion

Median nerve intraneural hypervascularity detected by color Doppler sonography is more accurate in detection of median nerve involvement than gray scale sonography criteria in patients with suspected carpal tunnel syndrome.     

高频超声对腕管综合征断面面积的测量研究

目的:研究高频超声定量测量腕管断面面积与腕管内容物断面面积之比,从而提高超声诊断腕管综合征的敏感性、特异性。方法:对经电生理及临床症状确诊的26例35侧患者组及30例60侧健康志愿者,高频超声测量豌豆骨水平及钩骨钩水平腕横韧带厚度、腕管断面积与腕管内容物断面积之比,采用ROC曲线分析测定各测量指标的诊断阈值,计算敏感度与特异度;并分析腕横韧带厚度与断面积比值之间相关性。结果:豌豆骨水平腕管断面积与腕管内容物断面积比值取最佳截点值2.447时,灵敏度为61.7%,特异度为77.1%。钩骨钩水平腕管断面积与腕管内容物断面积比值取最佳截点值2.177,灵敏度为83.3%,特异度为62.9%。腕横韧带厚度与断面积比值呈负相关性。结论:高频超声测量腕管断面积比值是诊断腕管综合征的一种有价值的新方法。     

High-resolution MRI predicts steroid injection response in carpal tunnel syndrome patients

Objectives

To correlate median nerve T2 signal and shape at the carpal tunnel with steroid injection (SI) response in carpal tunnel syndrome (CTS) patients.

Methods

One hundred and sixty-three CTS wrists of 92 consecutive patients who were scheduled to undergo SI were prospectively evaluated with 3-T magnetic resonance imaging (MRI) and a nerve conduction study. All patients underwent axial high-resolution T2-weighted MRI (in-plane resolution of 0.25?×?0.25 mm). The CTS wrists were classified into three groups according to the nerve T2 signal and the flattening ratio at the hook of hamate level: group 1, high and oval; group 2, high and flat; group 3, low and flat. Clinical response to SI was evaluated at 6 months after injection.

Results

One hundred and thirteen of the 163 wrists (69.3 %) responded well to SI. The percentage of improvement was 81.7 % (49/60) in group 1, 69.9 % (51/73) in group 2, and 43.3 % (13/30) in group 3 (P?<?0.01). On stepwise logistic regression analysis high-resolution MRI was the only significant independent factor for SI response in CTS patients (P?<?0.01).

Conclusions

High-resolution MRI correlates well with SI response in CTS patients and seems useful for predicting SI response.

Key Points

? MRI may help determine appropriate care in carpal tunnel syndrome. ? MRI helps in therapeutic decision-making whenever steroid injection is considered. ? T2 signal decrease of the median nerve correlates with poor outcome. ? T2 signal decrease of median nerve may reflect fibrosis and amyloid deposition.     

腕管综合征的MRI诊断

研究腕管综合征（CTS）的MRI特征及应用价值。材料和方法：经临床及手术证实的CTS12例，行MRI检查，以横断面为主。结果：12例CTS的MRI表现为：正中神经进入腕管时肿胀增粗12例，正中神经肿胀率（MNSR）为2．25：1。正中神经腕管内受压变扁12冽，正中神经扁平率（MNFR）为3．4。腕横韧带向掌侧膨隆10例，腕横韧带膨隆率（BR）为15．8％。T2WI像正中神经信号增高12例。结论：MRI对CTS的诊断、治疗方式的选择及疗效观察有重要的价值。     

Ultrasound features of carpal tunnel syndrome: a prospective case-control study

Purpose The purpose of the study was to examine the most adequate cut-off point for median nerve cross-sectional area and additional ultrasound features supporting the diagnosis of carpal tunnel syndrome (CTS). Material and methods Forty wrists from 31 CTS patients and 63 wrists from 37 asymptomatic volunteers were evaluated by ultrasound. All patients were women. The mean age was 49.1 years (range: 29–78) in the symptomatic and 45.1 years (range 24–82) in the asymptomatic group. Median nerve cross-sectional area was obtained using direct (DT) and indirect (IT) techniques. Median nerve echogenicity, mobility, flexor retinaculum measurement and the anteroposterior (AP) carpal tunnel distance were assessed. This study was IRB-approved and all patients gave informed consent prior to examination. Results In CTS the median nerve cross-sectional area was increased compared with the control group. Median nerve cross-sectional area of 10 mm² (DT) and 9 mm² (IT) had high sensitivity (85% and 88.5%, respectively), specificity (92.1% and 82.5%) and accuracy (89.3% and 82.5%) in the diagnosis of CTS. CTS patients had an increased carpal tunnel AP diameter, flexor retinaculum thickening, reduced median nerve mobility and decreased median nerve echogenicity. Conclusion Ultrasound assists in the diagnosis of CTS using the median nerve diameter cut-off point of 10 mm² (DT) and 9 mm² (IT) and several additional findings.     

Clinical, electrophysiological and MRI correlations in carpal tunnel syndrome]

Even though diagnosis of carpal tunnel syndrome is mainly based on clinical findings, other examinations are often useful for confirmation and management. The most useful of these examinations is EMG. However, EMG may be inconclusive and MRI may then be helpful. The indications for MRI in patients with carpal tunnel syndrome will be reviewed. METHOD: 20 patients with a total of 33 clinically suspected cases of carpal tunnel syndrome (CTS) underwent EMG and MRI evaluation. Clinical and EMG findings identified three groups of patients based on degree of deficit: mild, moderate, and severe. The following structures were evaluated at MRI: median nerve, retinaculum, retrotendinous fat, flexor tendons, thenar space, and muscles and bones of the wrist. Surgery was performed for 19 wrists. RESULTS: Only retinacular bowing and increased T2W signal intensity within the median nerve were significantly related to the diagnosis of CTS (sensitivity of 70% and 57% respectively). Retinacular bowing indicates increased "pressure" within the compartment (mechanical compression of the nerve) and increased T2W signal of the median nerve indicates nerve suffering. These findings correlated well with more severe cases based on clinical and EMG findings. CONCLUSION: In cases where there is discordance between clinical and EMG findings, MRI is helpful to identify patients who would benefit from surgical intervention.     

Median nerve cross-sectional area and MRI diffusion characteristics: normative values at the carpal tunnel

Objective  Enlargement of the median nerve is an objective potential imaging sign of carpal tunnel syndrome. Diffusion tensor MRI (DTI) may provide additional structural information that may prove useful in characterizing median neuropathy. This study further examines normal values for median nerve cross-sectional area (CSA), apparent diffusion coefficient (ADC), and fractional anisotropy (FA). Materials and methods  Twenty-three wrists in 17 healthy volunteers underwent MRI of the wrist at 3 T. In 13 subjects, DTI was performed at a B value of 600 mm²/s. Median nerve CSA, ADC, and FA were analyzed at standardized anatomic levels. Results  Mean (SD) median nerve CSA within the proximal carpal tunnel was 10.0 (3.4) mm². The mean (SD) FA of the median nerve was 0.71 (0.06) and 0.70 (0.13) proximal to and within the carpal tunnel, respectively. There was a significant difference between nerve CSA and ADC, but not FA, at the distal forearm and proximal carpal tunnel. Nerve CSA, ADC, and FA did not differ between men and women or between dominant and non-dominant wrists. Nerve CSA at the proximal carpal tunnel was positively correlated with subject age and body mass index. Conclusion  Our results suggest a 90% upper confidence limit for normal median nerve CSA of 14.4 mm² at the proximal carpal tunnel, higher than normal limits reported by many ultrasound studies. We observed a difference between the CSA and ADC, but not the FA, of the median nerve at the distal forearm and proximal carpal tunnel levels.     

Technical advances in ultrasound and MR imaging of carpal tunnel syndrome

The aim of this study was to compare the latest ultrasound-array technology to a conventional “high-resolution” transducer, modified MRI technique, and nerve conduction studies (NCS), in the diagnosis of carpal tunnel syndrome (CTS). In 19 normal wrists and 15 wrists with CTS, US with two different transducers was performed: a conventional linear-array transducer (LA) and a newly developed Multi-D linear-array transducer (MDA) were used. The US images were evaluated determining the swelling and the flattening ratios of the median nerve and correlated to respective findings in MRI (1.5 T) and to NCS. The NCS confirmed CTS in all 15 wrists. Measures of median nerve compression (swelling and flattening ratios) were significantly different in patients with CTS and controls (p < 0.01) with both types of US transducers and MRI. The MDA yielded higher correlation to MRI than the LA. Using critical values of 1.3 for the swelling and 3.4 for the flattening ratio, MRI, and US with the MDA yielded a sensitivity of 100 % each. Modern imaging modalities allow for an exact diagnosis of CTS even in cases with only slight median nerve pathology. Received: 24 June 1999; Revised: 8 October 1999; Accepted: 25 February 2000