Ultrasonography in the diagnosis of peripheral nerve disease

Ultrasound of the Ulnar Nerve: A Pictorial Review: Part 2: Pathological Ultrasound Findings

This is the second part of a two-part article in which we focus on the ultrasound (US) appearance of the pathological ulnar nerve (UN) and its main branches. Findings in a wide range of our pathological cases are presented with high-resolution US images obtained with the latest-generation US machines and transducers.

Transformer-Based Automated Segmentation of the Median Nerve in Ultrasound Videos of Wrist-to-Elbow Region

Segmenting the median nerve is essential for identifying nerve entrapment syndromes, guiding surgical planning and interventions, and furthering understanding of nerve anatomy. This study aims to develop an automated tool that can assist clinicians in localizing and segmenting the median nerve from the wrist, mid-forearm, and elbow in ultrasound videos. This is the first fully automated single deep learning model for accurate segmentation of the median nerve from the wrist to the elbow in ultrasound videos, along with the computation of the cross-sectional area (CSA) of the nerve. The visual transformer architecture, which was originally proposed to detect and classify 41 classes in YouTube videos, was modified to predict the median nerve in every frame of ultrasound videos. This is achieved by modifying the bounding box sequence matching block of the visual transformer. The median nerve segmentation is a binary class prediction, and the entire bipartite matching sequence is eliminated, enabling a direct comparison of the prediction with expert annotation in a frame-by-frame fashion. Model training, validation, and testing were performed on a dataset comprising ultrasound videos collected from 100 subjects, which were partitioned into 80, ten, and ten subjects, respectively. The proposed model was compared with U-Net, U-Net++, Siam U-Net, Attention U-Net, LSTM U-Net, and Trans U-Net. The proposed transformer-based model effectively leveraged the temporal and spatial information present in ultrasound video frames and efficiently segmented the median nerve with an average dice similarity coefficient (DSC) of approximately 94% at the wrist and 84% in the entire forearm region.

Contrast-enhanced ultrasonography for evaluation of the blood perfusion of sciatic nerves in healthy dogs

Blood supply to the peripheral nerves is essential for fulfilling their structural and functional requirements. This prospective, experimental, exploratory study aimed to assess the feasibility of contrast-enhanced ultrasonography (CEUS) for evaluating blood perfusion of the sciatic nerve in normal dogs. Contrast-enhanced ultrasonography examinations were performed on the bilateral sciatic nerves after bolus injection of Sonazoid™ (0.015 mL/kg) in 12 healthy Beagles for 150 s. Then, qualitative assessment of the wash-in timing, degree and enhancement patterns, and quantitative measurement of the peak intensity and time to peak intensity were performed from the sciatic nerve. The results were compared to those obtained from the adductor muscle around the nerve and caudal gluteal artery. After contrast agent injection, the sciatic nerve was enhanced at approximately 13-14 s, immediately after wash-in of the caudal gluteal artery. The peak intensity of the sciatic nerve was significantly lower than that of the caudal gluteal artery and higher than that of the adductor muscle. The time to peak intensity was significantly slower than that of the caudal gluteal artery; but was not significantly different from that of the adductor muscle. There were no significant differences in the peak intensity and time to peak intensity between the left and right sciatic nerves. These results demonstrate the feasibility of CEUS to assess blood perfusion of the sciatic nerve in healthy dogs qualitatively and quantitatively. This result from healthy dogs could serve as a reference for further studies that evaluate the sciatic nerve under pathological conditions.

Use of diffusion tensor imaging as a prognostic biomarker after decompression surgery for carpal tunnel syndrome

BACKGROUND

Magnetic resonance diffusion tensor imaging (MR-DTI) has been increasingly applied for carpal tunnel syndrome (CTS) diagnosis, but relatively little is known about the effect of CTS treatment on median nerve (MN) integrity and functional outcome prediction.

PURPOSE

To assess how structural changes in MR-DTI of the MN correlates with symptom severity, functional status, and electrophysiological parameters in patients suffering from CTS before and after decompression surgery.

MATERIAL AND METHODS

Nine wrists were prospectively enrolled to perform MR-DTI pre- and postoperatively. The apparent diffusion coefficients (ADC) and fractional anisotropy (FA) of the MN were examined in three different regions-distal radioulnar joint, pisiform bone, and hamate bone-and correlated with clinical and electrophysiological parameters.

RESULTS

Postoperatively, mean Boston Carpal Tunnel Questionnaire scores decreased 1.55 points (range = 0.08-3; P = 0.0172) and 1.01 points (-0.13 to 1.88; P = 0.0381) in the symptomatic and functional domains, respectively. Postoperative clinical improvement was reflected in proximal FA elevation (P = 0.0078), but not in diffusivity in comparison to baseline examination. Preoperative electrophysiological parameters were correlated with a reduction in the pre- (sensory latencies [rho = -0.6826; P = 0.0312]) and postoperative (motor latencies [rho = -0.7488; P = 0.0325]) distal FA values. Higher sensory amplitudes indicated higher postoperative proximal FA values (rho = 0.7618; P = 0.0280) ​​and lower postoperative proximal ADC values (rho = -0.9047; P = 0.0020).

CONCLUSION

Our study demonstrated that pre- and postoperative proximal FA values are useful biomarkers for the structural evaluation of the MN in patients with CTS. Symptomatic improvement can be better predicted by analyzing FA changes.

High-resolution ultrasound of peripheral neuropathies in rheumatological patients: An overview of clinical applications and imaging findings

Peripheral neuropathies are surprisingly common and can be associated with a number of conditions, including rheumatological diseases. Whether the co-existence of peripheral neuropathies with rheumatological disorders is coincidental or related to a common pathogenic mechanism, these disabling conditions can affect the outcome of rheumatological patients and should be targeted with specific treatment. The clinical presentation of peripheral neuropathy can be multifaceted and difficult to recognize in polysymptomatic patients. However, physicians adopting state-of-art diagnostic strategies, including nerve imaging, may improve the detection rate and management of neuropathies. In particular, a diagnostic approach relying exclusively on clinical history and nerve conduction studies may not be sufficient to disclose the etiology of the nerve damage and its anatomical location and thus requires integration with morphological studies. High-Resolution Ultrasound (HRUS) is increasingly adopted to support the diagnosis and follow-up of both joint disorders in rheumatology and peripheral neuropathies of different etiologies. In this review, the different types of nerve disorders associated with the most common syndromes of rheumatological interest are discussed, focusing on the distinctive sonographic features.

Reference values for the cross-sectional area of normal radial nerve at two levels using high-resolution ultrasonography

Aim of the study

High-resolution ultrasound is less often used to evaluate the radial nerves. The radial nerve is often involved in entrapment syndromes. The aim of the study is to establish the reference values for the cross-sectional area of the normal radial nerve on high-resolution ultrasonography, and to identify relationships between the cross-sectional area and the subject’s age, gender, height, weight, body mass index, and hand dominance.

Material and methods

The study was conducted on 200 subjects of both sexes, between 18 and 75 years of age, who did not have history of peripheral neuropathy or trauma to the upper limb. High-resolution real-time sonographic examination of the radial nerves was performed in both arms at two different levels. Level 1 was taken just proximal to the nerve bifurcation, and level 2 just after the nerve exits the spiral grove.

Results

The mean cross-sectional area measured at level 2 (4.3 ± 0.4 mm²) was greater than that measured at level 1 (2.3 ± 0.3 mm²). No significant relationship was seen with age and hand dominance (p >0.05), but the cross-sectional area values at above mentioned levels were larger in males than in females (p <0.05). In addition, the cross-sectional areas of the radial nerves showed a positive correlation with height, weight, and body mass index (p <0.05).

Conclusion

The established ultrasonographic reference values along with basic clinical data will aid in the diagnosis, response to treatment, and prognostic evaluation of peripheral neuropathies.

Cross-sectional area reference values for peripheral nerve ultrasound in adults: a systematic review and meta-analysis-Part I: Upper extremity nerves

BACKGROUND AND PURPOSE

Measurement of the cross-sectional area (CSA) of peripheral nerves using ultrasound is useful in the evaluation of focal lesions like entrapment syndromes and inflammatory polyneuropathies. Here, a systematic review and meta-analysis of published CSA reference values for upper extremity nerves was performed.

METHODS

Available to date nerve ultrasound studies on healthy adults were included and a meta-analysis for CSA was provided of the following nerves: median nerve at the wrist, forearm, upper arm; ulnar nerve at the Guyon's canal, forearm, elbow, upper arm; radial nerve at the upper arm. Regression and correlation analyses for age, gender, height, weight, geographic continents and publication year are reported.

RESULTS

Seventy-four studies with 4186 healthy volunteers (mean age 42.7 years) and 18,226 examined nerve sites were included. The calculated mean pooled CSA of the median nerve at the wrist was 8.3 mm² (95% confidence interval [95% CI] 7.9-8.7, n = 4071), at the forearm 6.4 mm² (95% CI 5.9-6.9, n = 3021), at the upper arm 8.3 mm² (95% CI 7.5-9.0, n = 1388), of the ulnar nerve at the Guyon's canal 4.1 mm² (95% CI 3.6-4.6, n = 1688), at the forearm 5.2 mm² (95% CI 4.8-5.7, n = 1983), at the elbow 5.9 mm² (95% CI 5.4-6.5, n = 2551), at the upper arm 6.6 mm² (95% CI 5.1-6.1, n = 1737) and of the radial nerve 5.1 mm² (95% CI 4.0-6.2, n = 1787). Substantial heterogeneity across studies (I² > 50%) was found only for the radial nerve. Subgroup analysis revealed a positive effect of age for the median nerve at the wrist and for height and weight for different sites of the ulnar nerve.

CONCLUSION

The first meta-analysis on CSA reference values for the upper extremities with no or only low heterogeneity of reported CSA values in most nerve sites is provided. Our data facilitate the goal of an international standardized evaluation protocol.

Back to the roots of rheumatology - Imaging of regional pain syndromes

Musculoskeletal regional pain syndromes (RPS) often lead to patient referrals in general and rheumatological practice. Detailed history taking and clinical examination can, in most cases, reveal the cause for pain and direct the subsequent management of the conditions. Yet, when in doubt, imaging methods, such as ultrasound (US) may support the clinical assessment. This paper reviews the underlying pathologies of some of the most frequently encountered RPS and the role of musculoskeletal US imaging for their diagnosis and treatment. If available, data on diagnostic accuracy and comparisons with gold standards are reported. The article stresses the importance of anatomical and sonoanatomical knowledge for the proper interpretation of the US images, points out the advantages and disadvantages of this imaging tool, and suggests the future research agenda.

Sciatic endometriosis: A narrative review of an unusual neurogynecologic condition

Endometriosis is a condition in which there is an ectopic growth of endometrial tissue. Sciatic endometriosis, otherwise known as catamenial sciatica, is a rare but exceedingly significant presentation of endometriosis. Symptoms include cyclic sciatic pain that peaks during the menstrual period; additionally, paresthesia, paresis, and areflexia may occur with this condition. Sciatic endometriosis can be presumptively diagnosed in response to empiric treatment (e.g. gonadotropin-releasing hormone analogs) or imaging studies, but a definitive diagnosis of sciatic endometriosis may occur from examining tissue obtained during surgery. Surgical removal of endometriosis from the sciatic nerve root can potentially eliminate symptoms while maintaining normal reproductive function, though poses particular surgical risks. Familiarity with this rare condition is paramount to making this diagnosis and the initiation of earlier treatment.

High-Resolution Nerve Ultrasound to Assess Nerve Echogenicity, Fascicular Count, and Cross-Sectional Area Using Semiautomated Analysis

BACKGROUND AND PURPOSE

Little is known about echogenicity and fascicular structure observed in high-resolution nerve ultrasound (HRUS) in both healthy subjects and patients with peripheral nerve disease. The aim of this study was to evaluate the reliability of echogenicity, fascicle count, and fascicle size analysis, to create standard values and compare these parameters to patients with chronic inflammatory demyelinating polyneuropathy (CIDP).

METHODS

Median, ulnar, radial, tibial, and fibular nerve of 79 healthy subjects and patients were scanned by one examiner using HRUS. Image analysis regarding echogenicity, fascicle count, and fascicle cross-sectional area (CSA) was performed by two independent raters semiautomatically using ImageJ. Pearson correlation coefficient r reflected interrater reliability (IR), and intraclass correlation coefficient (ICC) determined intrarater reliability (IAR). Results of healthy subjects were compared to 20 patients with CIDP by analysis of variance.

RESULTS

IR was very good for echogenicity (r = .9) and good for fascicle count and size of the largest fascicle (r = .64/.56). IAR was very good for all three parameters (ICC = .9/.83/.74). Healthy subjects had a wide range of values. CIDP patients were in range of healthy subjects. Clinically progressive CIDP patients (defined as an increase in Overall Disability Sum Score by ≥1 point) had a lower fraction of black than healthy controls and stable CIDP patients (P < .001).

CONCLUSION

Semiautomated evaluation of echogenicity, fascicle count, and fascicle CSA is reliable. Cutoff values to differentiate between healthy persons and CIDP do not exist. Echogenicity is useful for detecting clinically progressive CIDP patients and should be used in clinical context or intraindividual course.

Nerve ultrasound: A reproducible diagnostic tool in peripheral neuropathy

OBJECTIVE

To determine interobserver variability of nerve ultrasound in peripheral neuropathy in a prospective, systematic, multicenter study.

METHODS

We enrolled 20 patients with an acquired chronic demyelinating or axonal polyneuropathy and 10 healthy controls in 3 different centers. All participants underwent an extensive nerve ultrasound protocol, including cross-sectional area measurements of median, ulnar, fibular, tibial, and sural nerves, and brachial plexus. Real-time image acquisition was performed blind by a local and a visiting investigator (reference). Five patients were investigated using different types of sonographic devices. Intraclass correlation coefficients were calculated, and a random-effects model was fitted to identify factors with significant effect on interobserver variability.

RESULTS

Systematic differences between measurements made by different investigators were small (mean difference 0.11 mm2 [95% confidence interval 0.00-0.23 mm2]). Intraclass correlation coefficients were generally higher in arm nerves (0.48-0.96) than leg nerves (0.46-0.61). The hospital site and sonographic device did not contribute significantly to interobserver variability in the random-effects model.

CONCLUSIONS

Interobserver variability of nerve ultrasound in peripheral neuropathy is generally limited, especially in arm nerves. Different devices and a multicenter setting have no effect on interobserver variability. Therefore, nerve ultrasound is a reproducible tool for diagnostics in routine clinical practice and (multicenter) research.

Ultrasonographic Reference Values for Assessing Normal Sciatic Nerve Ultrasonography in the Normal Population

Objective:

High-resolution ultrasonography (HRUS) has been used recently to characterize median and ulnar nerves but is seldom used to characterize the lower extremity nerves. The reference standard for normal the lower extremity nerves has not been established. Thus, this study measured the cross-sectional areas (CSAs) of the sciatic nerve of 200 healthy male or female volunteers, aged 18–80 using HRUS. These data provide basic clinical data for the use of high-resolution ultrasound for the future diagnosis, treatment, and prognostic evaluation of peripheral neuropathies.

Methods:

Two hundred healthy volunteers with 400 lower extremities were studied with HRUS. According to their age, the subjects were assigned to young group (18-30 years, n = 75), middle group. (31-60 years, n = 70), and old group(61-80 year, n = 55). Age, sex, height, weight were recorded and CSAs of sciatic nerve were obtained at every predetermined sites.

Results:

The mean CSAs of sciatic nerves at GS and MGPF were 0.527 ± 0.028 cm² and 0.444 ± 0.026 cm² respectively. Pearson's correlation analysis showed that the mean CSAs were correlated with height and weight. There was no difference in mean CSAs among the three groups (P > 0.05). Women had smaller CSAs of the normal Sciatic nerves than men in two measuring sites (GS, MGPF) (P < 0.05).

Conclusion:

Peripheral nerve ultrasonography is a reliable and reproducible diagnostic method in the hands of experienced examiners. Normal values for the sciatic nerve nerves are provided by our study. Thus, reference values of Sciatic nerve CSA of the lower extremity can facilitate the analysis of abnormal nerve conditions.

Electrophysiological examination and high frequency ultrasonography for diagnosis of radial nerve torsion and compression

This study aims to evaluate the value of electrophysiological examination and high frequency ultrasonography in the differential diagnosis of radial nerve torsion and radial nerve compression.Patients with radial nerve torsion (n = 14) and radial nerve compression (n = 14) were enrolled. The results of neurophysiological and high frequency ultrasonography were compared.Electrophysiological examination and high-frequency ultrasonography had a high diagnostic rate for both diseases with consistent results. Of the 28 patients, 23 were positive for electrophysiological examination, showing decreased amplitude and decreased conduction velocity of radial nerve; however, electrophysiological examination cannot distinguish torsion from compression. A total of 27 cases showed positive in ultrasound examinations among all 28 cases. On ultrasound images, the nerve was thinned at torsion site whereas thickened at the distal ends of torsion. The diameter and cross-sectional area of torsion or compression determined the nerve damage, and ultrasound could locate the nerve injury site and measure the length of the nerve.Electrophysiological examination and high-frequency ultrasonography can diagnose radial neuropathy, with electrophysiological examination reflecting the neurological function, and high-frequency ultrasound differentiating nerve torsion from compression.

Longitudinal Changes in Glucose Metabolism of Denervated Muscle after Complete Peripheral Nerve Injury

PURPOSE

Electrodiagnostic studies can obtain information 2 or 3 weeks after an acute nerve injury. Previous studies have shown increased glucose metabolism in denervated muscles 1 week after injury using 2-deoxy-2-[(18)F]fluoro-D-glucose ([(18)F]FDG) positron emission tomography (PET). Therefore, this study aimed to evaluate the changes in glucose metabolism in denervated muscles using serial monitoring by [(18)F]FDG PET scans.

PROCEDURES

Denervation was induced in eight male Sprague-Dawley rats (aged 7 weeks old) weighing 200-250 g. The right legs of the rats were denervated by resecting the sciatic nerve in the thigh after the initial skin incision. Two rats were sacrificed 1 and 10 weeks after denervation. Skeletal muscles (gastrocnemius and tibialis anterior) were excised from both the right and left legs of the rats. Staining with hematoxylin and eosin, glucose transporter (GLUT)-1, GLUT-4, and hexokinase II was undertaken. PET/computed tomography (CT) scans were performed on the six remaining rats a total of five times at 1, 2, 5, 8, and 10 weeks after denervation. Regions of interest were drawn on integrated PET/CT images to measure the degree of [(18)F]FDG uptake in the right and left lower leg muscles. Target-to-background ratios (TBRs) were calculated by dividing the FDG uptake of the lower leg muscles by that of the upper leg muscles.

RESULTS

The TBRs of the denervated muscles were higher than those of the control muscles at both 1 (6.84 ± 1.98 vs. 1.18 ± 0.11, p = 0.009) and 2 (4.10 ± 2.05 vs. 1.86 ± 0.73, p = 0.0374) weeks after denervation. After 5 (2.18 ± 0.78 vs. 1.35 ± 0.47, p = 0.1489), 8 (1.76 ± 0.18 vs. 1.69 ± 0.18, p = 0.5127), and 10 (1.76 ± 0.52 vs. 1.56 ± 0.37, p = 0.5637) weeks, the difference in the TBRs between the denervated and controls became non-significant.

CONCLUSIONS

[(18)F]FDG PET can visualize increased glucose metabolism in a denervated muscle early as 1 week after injury. Therefore, PET could be adopted as a noninvasive imaging modality for acute nerve injuries. In addition, [(18)F]FDG PET may help to understand the role of the nervous system in the control of peripheral tissues.

Role of sonography in the diagnosis and treatment of a ganglion cyst compressing the lateral branch of deep peroneal nerve

Selective compression neuropathy of the lateral branch of the deep peroneal nerve is rare. A 55-year-old woman with ankle instability and mild weakness of extension of the toes was examined with sonography (US), which revealed the presence of a ganglion cyst compressing selectively the lateral branch of the deep peroneal nerve. US-guided aspiration of the cyst resulted in nerve decompression and progressive resolution of symptoms. This case demonstrates the importance of examining the deep peroneal nerve and its branches when performing US in the clinical setting of ankle instability. © 2016 Wiley Periodicals, Inc. J Clin Ultrasound 45:108-111, 2017.

US of the Peripheral Nerves of the Upper Extremity: A Landmark Approach

Ultrasonography (US) has become a first-line modality for the evaluation of the peripheral nerves of the upper extremity. The benefits of US over magnetic resonance (MR) imaging include higher soft-tissue resolution, cost effectiveness, portability, real-time and dynamic imaging, and the ability to scan an entire extremity quickly and efficiently. US can be performed on patients who are not eligible for MR imaging. Metallic implant artifacts are usually not problematic. US has been shown to have equal specificity and greater sensitivity than MR imaging in the evaluation of peripheral nerves. Any abnormal findings can be easily compared with the contralateral side. The published literature has shown that US has demonstrated clinical utility in patients with suspected peripheral nerve disease by guiding diagnostic and therapeutic decisions as well as by confirming electrodiagnostic findings. Common indications for upper extremity peripheral nerve US are the evaluation for injury due to penetrating trauma, entrapment by scar tissue, and tumor. US of the upper extremity is most commonly performed to evaluate carpal and cubital tunnel syndrome. It is important for the radiologist or sonographer to have a detailed knowledge of anatomy and specific anatomic landmarks for each nerve to efficiently and accurately perform an examination. The goal of this article is to introduce readers to the basics of US of the peripheral nerves of the upper extremity with a focus on the median, ulnar, and radial nerves. Common sites of disease and the location of important anatomic landmarks will be reviewed.

Ultrasonographic Identification of Fibromuscular Bands Associated with Neurogenic Thoracic Outlet Syndrome: The "Wedge-Sickle" Sign

Thoracic outlet syndrome (TOS) is a disorder characterized by compression of the lower trunk of the brachial plexus, most often in association with anomalous congenital fibromuscular bands in the scalenic region. Early diagnosis is important, because the neurologic deficit associated with TOS may be irreversible. Using high-resolution ultrasound, we investigated 20 consecutive patients with clinical signs suggestive of TOS (all females, average age: 40.4 ± 14.9 y) and 25 control patients. In 19 patients, we identified a hyper-echoic fibromuscular structure at the medial edge of the middle scalene muscle, which indented the lower trunk of the brachial plexus ("wedge-sickle sign"). It was associated with the significant enlargement (p < 0.0001) and hypo-echogenicity of the lower trunk. This novel and distinctive ultrasonographic sign allows pre-surgical identification of anomalous fibromuscular bands causing TOS. It is especially useful in patients without neurologic deficit, in whom the diagnosis may not be as straightforward.

Peripheral nerve imaging: Not only cross-sectional area

Peripheral nerve imaging is recognized as a complement to clinical and neurophysiological assessment in the evaluation of peripheral nerves with the ability to impact patient management, even for small and difficult nerves. The European Society of Musculoskeletal Radiology, suggest to use ultrasound (US) for nerve evaluation due to the fact that, in sever anatomical area, magnetic resonance imaging is not able to give additional informations. US could be considered the first-choice approach for the assessment of peripheral nerves. The relative drawback of peripheral nerve US is the long learning curve and the deep anatomic competence to evaluate even small nerves. In the recent years, the role of US in peripheral nerve evaluation has been widened. In the past, nerve US was mainly used to assess nerve-cross sectional area, but now more advanced measurements and considerations are desirable and can boost the role of peripheral nerve US. Nerve echotexture evaluation was defined in 2010: The ratio between the hypoechoic and hyperechoic areas of peripheral nerves on US was called “nerve density”. For evaluation of patients who have peripheral neuropathies, the role of peripheral nerve is US wider than simple cross-sectional area evaluation. Quantitative measurements describing the internal fascicular echotexture of peripheral nerves introduce the concept of considering US as a possible quantitative imaging biomarker technique. The potential of nerve US has started to be uncovered. It seems clear that only cross-sectional area measurement is no more sufficient for a comprehensive US evaluation of peripheral nerves.

US of the Peripheral Nerves of the Lower Extremity: A Landmark Approach

Ultrasonography (US) is commonly used to assess the peripheral nerves of the lower extremity because of its many advantages over magnetic resonance (MR) imaging. The most obvious advantages over MR imaging are superior soft-tissue resolution, low cost, portability, lack of magnetic susceptibility artifact, and the ability to image patients who cannot undergo MR imaging. US has been shown to have equal specificity and greater sensitivity than MR imaging in the evaluation of peripheral nerves. Additional benefits are the capability of real-time and dynamic imaging, and the ability to scan an entire extremity quickly without the need for a patient to lie motionless for long periods of time, as with MR imaging. Any abnormal findings can be easily compared against the contralateral side. Published literature has shown that US has clinical utility in patients suspected of having peripheral nerve disease: US can be used to guide diagnostic and therapeutic decisions, as well as help confirm electrodiagnostic findings. Common indications for lower extremity peripheral nerve US are the evaluation for injury due to penetrating trauma, entrapment by scar tissue, or tumor. To confidently perform US of the peripheral nerves of the lower extremity, it is important to gain a thorough knowledge of anatomic landmarks and the course of each nerve. Readers who may not be familiar with US will be introduced to the basics of scanning the peripheral nerves of the lower extremity. Important anatomic landmarks and common sites of injury and entrapment will be reviewed.

High-resolution ultrasound of peripheral nerves in systemic sclerosis: a pilot study of computer-aided quantitative assessment of nerve density

OBJECTIVES

To quantitatively evaluate and compare nerve density in patients with limited cutaneous systemic sclerosis (lcSSc) and control subjects using high-resolution ultrasound (US) with a computer-aided assessment.

METHODS

Forty patients and 40 age- and sex-matched control subjects were prospectively enrolled. Ultrasound (US) examination (17-5 MHz probe) of the median nerve at the elbow was performed bilaterally by one radiologist. A software quantified the ratio between the hypoechoic and hyperechoic areas of peripheral nerves on ultrasound. Two observers set the threshold in the images acquired, and three observers performed the digital analysis of nerve density. Statistical analysis included Mann-Whitney U-test of patients versus control subjects and subgroup analysis of symptomatic and non-symptomatic patients. Intra and inter-observer agreement of the three observers were assessed with the kappa statistic.

RESULTS

In all, 160 median nerves were evaluated. According to the US, nerve density was significantly reduced in lcSSc patients compared to control subjects (mean and standard deviation: 41 ± 3 vs 56 ± 4, p < 0.01). Subgroup analysis showed that symptomatic patients (n = 15) had reduced nerve density compared to non-symptomatic (n = 25) patients (39 ± 5 vs 43 ± 4, p < 0.01). Intra-observer agreement was very good (K = 0.82). Inter-observer agreements were good: reader 1 vs reader 2: k = 0.78 (95% confidence interval 0.65 to 0.91); reader 2 vs reader 3: k = 0.72 (95% confidence interval 0.65 to 0.82); reader 3 vs reader 1: k = 0.71 (95% confidence interval 0.64-0.81).

CONCLUSIONS

In lcSSc patients, nerve density was reduced, especially in the symptomatic group, compared to control subjects.

Does the ratio of the carpal tunnel inlet and outlet cross-sectional areas in the median nerve reflect carpal tunnel syndrome severity?

Although ultrasound measurements have been used in previous studies on carpal tunnel syndrome to visualize injury to the median nerve, whether such ultrasound data can indicate the severity of carpal tunnel syndrome remains controversial. The cross-sectional areas of the median nerve at the tunnel inlet and outlet can show swelling and compression of the nerve at the carpal. We hypothesized that the ratio of the cross-sectional areas of the median nerve at the carpal tunnel inlet to outlet accurately reflects the severity of carpal tunnel syndrome. To test this, high-resolution ultrasound with a linear array transducer at 5-17 MHz was used to assess 77 patients with carpal tunnel syndrome. The results showed that the cut-off point for the inlet-to-outlet ratio was 1.14. Significant differences in the inlet-to-outlet ratio were found among patients with mild, moderate, and severe carpal tunnel syndrome. The cut-off point in the ratio of cross-sectional areas of the median nerve was 1.29 between mild and more severe (moderate and severe) carpal tunnel syndrome patients with 64.7% sensitivity and 72.7% specificity. The cut-off point in the ratio of cross-sectional areas of the median nerve was 1.52 between the moderate and severe carpal tunnel syndrome patients with 80.0% sensitivity and 64.7% specificity. These results suggest that the inlet-to-outlet ratio reflected the severity of carpal tunnel syndrome.

Age-related differences in the quantitative echo texture of the median nerve

OBJECTIVES

Currently, there are no quantitative data on the echo texture of a peripheral nerve. This study was designed to objectively compare the differences in the echo texture of the median nerve in the young and the elderly.

METHODS

The median nerves of 10 healthy young volunteers (<30 years old; group Y) and 10 elderly patients undergoing lower limb surgery (>60 years old; group E) were scanned at the mid forearm by a standardized protocol. The echo texture of a normalized median nerve image was analyzed for the echo intensity and spatial distribution of pixels. Noise in the image was reduced by using a median filter, and thresholding was performed thereafter. In the resultant binary image, the cross-sectional area, echo intensity, white area index, and black area index of the median nerve were determined by computerized texture analysis.

RESULTS

The mean cross-sectional area of the median nerve in group E was significantly smaller than that in group Y (P = .002). The mean echo intensity and white area index in group E were significantly higher than those in group Y (P= .002 and .012). The mean black area index in group E was correspondingly significantly lower than that in group Y (P = .012). In group Y, the mean white area index was significantly lower than the black area index (P = .006) but not in group E (P = .213).

CONCLUSIONS

There are significant differences in the echo texture of the median nerve between the young and the elderly. These differences may be due to age-related changes in the relative proportion of neural fascicles and connective tissue within the nerve.

Ultrasonographic reference values for assessing normal radial nerve ultrasonography in the normal population

High-resolution ultrasound has been used recently to characterize median and ulnar nerves, but is seldom used to characterize radial nerves. The radial nerve is more frequently involved in entrapment syndromes than the ulnar and median nerves. However, the reference standard for normal radial nerves has not been established. Thus, this study measured the cross-sectional areas of radial nerves of 200 healthy male or female volunteers, aged 18 to 75, using high-resolution ultrasound. The results showed that mean cross-sectional areas of radial nerves at 4 cm upon the lateral epicondyle of the humerus and mid-humerus (midpoint between the elbow crease and axilla) were 5.14 ± 1.24 and 5.08 ± 1.23 mm², respectively. The age and the dominant side did not affect the results, but the above-mentioned cross-sectional areas were larger in males (5.31 ± 1.25 and 5.19 ± 1.23 mm²) than in females (4.93 ± 1.21 and 4.93 ± 1.23 mm², respectively). In addition, the cross-sectional areas of radial nerves were positively correlated with height and weight (r = 0.38, 0.36, respectively, both P < 0.05). These data provide basic clinical data for the use of high-resolution ultrasound for the future diagnosis, treatment, and prognostic evaluation of peripheral neuropathies.

The effect of magnification on sonographically measured nerve cross-sectional area

INTRODUCTION

The primary aim of this investigation was to determine whether use of write-zoom magnification affects sonographically determined cross-sectional area (CSA) of peripheral nerves.

METHODS

CSAs of the median (MN) and posterior interosseous (PIN) nerves were measured in 22 limbs from 11 asymptomatic volunteers using both standard imaging and write-zoom magnification. CSA measurements were repeated on the same images 1 week later.

RESULTS

The average CSA of write-zoomed images for the MN was significantly larger at both measurement sessions (week 1: 11.1 mm(2) write-zoom vs. 10.0 mm(2) standard, P = 0.019; week 2: 11.8 mm(2) vs. 10.4 mm(2), P = 0.023). Similar differences were noted for the PIN (week 1: 2.3 mm(2) vs. 1.9 mm(2), P = 0.002; week 2: 2.5 mm(2) vs. 1.9 mm(2), P = 0.001).

CONCLUSIONS

Write-zoom magnification may significantly increase the measured CSA of peripheral nerves. These changes appear to be more substantial when smaller nerves are measured.

Cross-sectional area reference values of nerves in the lower extremities using ultrasonography

INTRODUCTION

Cross-sectional area (CSA) reference values of lower extremity nerves using ultrasonography have only been reported in a few studies and have been limited to white populations.

METHODS

For this study, 94 healthy Korean volunteers were recruited for measurement of the CSA at 7 sites of lower extremity nerves. The side-to-side difference in CSA was calculated for each nerve, and reference ranges were derived. External validity evaluation for the reference values was performed with 10 newly recruited volunteers at a different institution.

RESULTS

Nerve CSA was correlated significantly with body mass index, weight, and height; however, the absolute value of the side-to-side difference had no significant correlation with demographic factors. The external validity was adequate for all sites, ranging from 80% to 100%.

CONCLUSIONS

The lower extremity nerve CSA values obtained in this study may provide normal reference values for the Asian population.

A comparison of ultrasonographic and electrophysiologic 'inching' in ulnar neuropathy at the elbow

OBJECTIVE

The present study aimed to clarify the relationship between structural ulnar nerve changes and electrophysiological nerve dysfunction in patients with ulnar neuropathy at the elbow (UNE).

METHODS

High-resolution ultrasonography of the ulnar nerve was performed on 17 limbs with clinically and electrophysiologically confirmed UNE, and 52 control subjects at four standardised sites proximal and distal to the medial epicondyle (P2, P1, D1, D2), corresponding to segments of ulnar short-segment nerve conduction studies ("inching studies").

RESULTS

Ulnar nerve cross-sectional area (CSA) and hypoechoic fraction were significantly increased in patients with UNE immediately distal (D1) and proximal (P1) to the medial epicondyle (p<0.01). In patients with UNE, hypoechoic fraction was similar in asymptomatic and symptomatic limbs. Motor nerve conduction velocity across the elbow correlated with CSAmax and the maximum hypoechoic fraction (R=0.6, p<0.05). CSA and hypoechoic fraction of individual segments did not correlate with corresponding latencies on inching studies, but latencies across the D1 segment correlated with CSA at P1 (R=0.80, p<0.0001) and D2 (R=0.65, p<0.01).

CONCLUSIONS

Sonographic abnormalities in UNE may not be maximal at the site of electrophysiological nerve dysfunction.

SIGNIFICANCE

Sonographic abnormalities may reflect secondary pathophysiological changes in segments adjacent to regions of nerve compression.

Different patterns of nerve enlargement in polyneuropathy subtypes as detected by ultrasonography

The purpose of our study was to examine how the pathologic type of polyneuropathy affects nerve size as assessed by high-resolution ultrasonography with a 15 MHz transducer. Cross-sectional area (CSA) of the C5-C7 nerve roots and several upper and lower limb nerves at multiple sites was measured in 38 patients with acquired diffuse sensorimotor demyelinating or axonal polyneuropathy and in 34 healthy control subjects. Significant differences were found among the groups for all nerve and root segments: Both types of polyneuropathy are characterized by nerve enlargement in comparison to controls, but in different patterns. In demyelinating polyneuropathies, an additional degree of nerve thickening appears in proximal upper limb nerves and cervical nerve roots compared with axonal polyneuropathies. With respect to the other nerves, a similar degree of nerve enlargement was observed in both patient groups. These results highlight that ultrasonography may be a complementary tool in differentiating polyneuropathies.

[Rupture by attrition of the median nerve found during a carpal tunnel release procedure]

We report the finding of a subtotal rupture of the median nerve caused by a "bridge" or"easel" erosion due to a sequela of childhood wrist fracture. This unpublished observation was made during a carpal tunnel release procedure on an 80-year-old patient who was operated on for recurrence of a severe carpal tunnel syndrome 30 years after a previous neurolysis. If the flexor tendon ruptures are widely described, as well as nerve sections following high energy trauma, the median nerve rupture caused by its erosion over a bony projection has never been published at the best of our knowledge.

Sonographic visualization of the first branch of the lateral plantar nerve (baxter nerve): technique and validation using perineural injections in a cadaveric model

OBJECTIVES

The primary purpose of this investigation was to document the ability of high-resolution sonography to accurately identify the first branch of the lateral plantar nerve (FBLPN) using sonographically guided perineural injections in an unembalmed cadaveric model.

METHODS

single experienced operator completed sonographically guided perineural FBLPN injections in 12 unembalmed cadaveric specimens (6 right and 6 left) obtained from 10 donors (5 male and 5 female) aged 47 to 95 years (mean, 71 years) with an average body mass index of 24.2 kg/m(2) (range, 17.2-31.6 kg/m(2)). All injections were completed using 22-gauge, 38-mm stainless steel needles to deliver 1 mL of 50% diluted colored latex adjacent to the FBLPN in the abductor hallucis-quadratus plantae (AH-QP) interval. Six injections were completed using a cart-based ultrasound (US) machine and a 17-5-MHz transducer, and 6 were completed using a portable US machine and a 12-3-MHz transducer. Nerve conspicuity was graded on a 4-point scale (1, poor; 4, excellent). After a minimum of 24 hours, study coinvestigators dissected each specimen to assess injectate placement.

RESULTS

All 12 injections accurately placed latex onto the FBLPN within the AH-QP interval, with 11 of 12 (91%) resulting in complete nerve coverage. Proximal latex overflow to the lateral plantar nerve occurred in 82% of cases (10 of 12). The average distance between the plantar fascia and injected latex was 1.2 cm (range, 1.0-1.75 cm). No vascular injury was seen in any specimen. The average nerve conspicuities were 3.7 (range, 3-4) using the cart-based US machine and 1.8 (range, 1-4) using the portable US machine.

CONCLUSIONS

Sonographic visualization of the FBLPN in the AH-QP interval is feasible and should be considered for diagnostic and therapeutic purposes in patients presenting with chronic or atypical heel pain syndromes. Further clinical experience should refine the role of FBLPN sonography and explore the utility of sonographically guided diagnostic and therapeutic FBLPN perineural injections.

Entrapment syndrome of multiple nerves in graft-versus-host disease

INTRODUCTION

Peripheral nerve entrapment syndromes are associated with hereditary neuropathy with liability to pressure palsies and a variety of rheumatic and endocrinological diseases.

METHODS

We report a patient with entrapment syndromes of multiple nerves associated with chronic graft-versus-host-disease (GVHD) after allogeneic hematopoietic stem cell transplantation. Nerve ultrasound, histology, and ultrastructural changes were assessed.

RESULTS

The 51-year-old man had developed severe deep dermal sclerosis due to chronic GVHD with a progressive polyneuropathy and entrapment syndromes of multiple nerves. Pre-stenotic enlargement was shown by nerve ultrasound. Histology demonstrated fibrosis of the epineurium with scarce infiltration of macrophages. Electron microscopy demonstrated alterations of the myelin sheaths and marked depletion of normal-sized myelinated nerve fibers.

CONCLUSIONS

In addition to polyneuropathy, chronic GVHD can be associated with peripheral nerve entrapment syndromes and should be added to the differential diagnosis of compressive neuropathies.