Cross-sectional area reference values for nerve ultrasonography

Ultrasound allows for a non-invasive structural assessment of nerves, muscles, and surrounding tissues, and therefore it is increasingly being used as a supplement to traditional electrodiagnostic studies. As investigators have begun to use ultrasound to explore peripheral nerves, it has become clear that conditions such as entrapment, hereditary neuropathies, acquired neuropathies, trauma, and nerve tumors result in an increase in nerve cross-sectional area. Reference values have not been published for the cross-sectional area of many nerves commonly studied in diseases of the peripheral nervous system, so our goal was to obtain reference values for the nerve cross-sectional area at the following sites: radial at antecubital fossa; radial at distal spiral groove; musculocutaneous in upper arm; trunks of the brachial plexus; vagus at carotid bifurcation; sciatic in distal thigh; tibial in popliteal fossa; tibial in proximal calf; tibial at ankle; peroneal in popliteal fossa; peroneal at fibular head; and sural in distal calf. Mean cross-sectional area, as well as side-to-side differences, are reported for each site, and qualitative data are provided to guide imaging at each site. The information provided in this study should serve as the starting point for quantitatively evaluating these nerve sites with ultrasound.     

Influence of body mass index on median nerve function, carpal canal pressure, and cross-sectional area of the median nerve

Obese individuals have slowed conduction in the median nerve across the wrist, but the mechanism for this is not established. This case-control study of 27 obese subjects and 16 thin subjects was designed to test the hypothesis that obese individuals have higher carpal canal pressures and more median nerve swelling than thin individuals. All subjects were asymptomatic for hand symptoms, and had measurements of median and ulnar sensory nerve conduction in the nondominant hand, ultrasound measurement of the median nerve cross-sectional area proximal to the carpal canal, and carpal canal pressure measurement. There was no difference in age or gender ratio between the obese and thin groups. The median nerve cross-sectional area was equal in the obese and thin groups (9.3 mm2 vs. 9.4 mm2), as was the carpal canal pressure (16.2 mmHg vs. 15.5 mmHg, respectively). There was a strong correlation between median nerve conduction slowing across the wrist and median nerve cross-sectional area at the wrist (r = 0.55, P = 0.002). Obesity does not influence carpal canal pressure or the size of the median nerve at the wrist. However, there is a strong association between slowed median nerve conduction and increased nerve size which suggests endoneurial edema as a metabolic mechanism; the conduction slowing does not appear to be related to mechanical stress.     

Repeatability of ultrasonographic median nerve measures

In this study we investigated the reliability of ultrasound in measuring median nerve characteristics including cross‐sectional area (CSA), flattening ratio (FR), swelling ratio (SR), and mean grayscale. Generalizability theory was used to assess inter‐ and intrarater reliability using the dependability coefficient (?), normalized standard error of measurement, and normalized minimum detectable change (MDC_NORM) for multiple study design protocols. Interrater reliability was generally moderate. Intrarater reliability was mostly good (? > 0.876) when using a single image, captured on one occasion, and being read once. Intrarater MDC_NORM ranged from 3.8% to 6.2% for all CSA measures and SR. Using multiple images and/or readings at multiple occasions did not appreciably improve reliability measures. Ultrasound is a reliable tool for measuring median nerve characteristics. We recommend that a single evaluator capture all images for protocols aimed at quantifying median nerve ultrasound measures. We believe an appropriately designed protocol can utilize ultrasound to accurately assess changes in median nerve characteristics after activity. Muscle Nerve, 2010     

Median nerve ultrasound as a screening tool in carpal tunnel syndrome: Correlation of cross‐sectional area measures with electrodiagnostic abnormality

Introduction: Sonographically measured median nerve cross‐sectional area (CSA) at the wrist is increased in patients with carpal tunnel syndrome (CTS). Ultrasound of the median nerve may be useful in screening for electrodiagnostic (EDx) abnormalities. Methods: EDx studies were performed on all participants. Sonographic evaluation of median nerve CSA at the wrist and in the forearm was performed by a physician blinded to the EDx results. Multivariate and receiver operating characteristic (ROC) analysis were used to assess the data. Results: Fifty control wrists and 192 symptomatic wrists were analyzed. Sensitivity of ultrasound in excluding EDx abnormality was 99% for CSA of 9 mm² and 97% for a wrist–forearm ratio (WFR) of 1.4. There was no clinically significant correlation between ultrasound parameters and EDx severity. Conclusions: Median nerve ultrasound is a highly sensitive screening tool for EDx abnormality, but it cannot determine severity. This may lead to changes in the current standards for evaluating CTS. Muscle Nerve, 2012     

Median nerve penetration by a persistent median artery and vein mimicking carpal tunnel syndrome

Introduction: Carpal tunnel syndrome (CTS) is a common clinical syndrome seen in the outpatient setting that is easily confirmed by electrodiagnostic testing. Methods: We describe the case of a patient who presented with the classic symptoms and neurological examination for CTS, but had a normal nerve conduction study and electromyogram. Results: Neuromuscular ultrasound of the median nerve on the symptomatic side revealed penetration of the nerve by a persistent median artery and vein in the mid‐forearm, with a positive sonographic Tinel sign over this spot. This finding is an anatomical variation that has been described sparingly in the literature, mostly in cadavers. It has not been reported previously to be a mimic of CTS. Conclusions: This case demonstrates the diagnostic utility of neuromuscular ultrasound and the importance of considering an anatomical variation involving the median nerve in the differential diagnosis of CTS. Muscle Nerve 53: 485–487, 2016     

Transient forearm conduction block in the median nerve

We present two cases referred for electrophysiological confirmation of carpal tunnel syndrome (CTS). Initial nerve conduction studies were normal. Approximately 20 min into the examination, both patients developed sensory symptoms and weakness in the distal median nerve territory while the elbow was extended and forearm supinated. Further studies demonstrated complete conduction block across the forearm in the median motor and sensory nerve fibers. When measurable, conduction velocities remained normal or were modestly slow. Complete clinical and electrophysiological recovery occurred within 2 min following forearm pronation, suggesting that dysfunction was probably due to focal transient ischemia. Patients describing increased sensory symptoms during routine electrophysiological assessments for CTS should be investigated to rule out the possibility of a more proximal abnormality.     

高频超声对上肢桡神经检测正常参考值的研究

目的测量正常人上肢桡神经在高频超声(HUS)下神经形态、声像学特点及横截面积(CSA)的正常值并探讨神经与周围组织的关系;为高频超声检侧外周神经疾病提供正常参考值。方法对临床检查正常的200例健康志愿者沿桡神经在神经预定的测量点上依次获取超声声像图及测量各点神经的横截面积,每个测量点重复测量三次取其平均值,并做神经CSA与身高、体重的相关性分析。结论高频超声下正常人上肢神经呈筛网状低回声图像,横截面呈圆形、卵圆形或三角形。测量桡神经各测量点处的神经横截面积,桡神经在肱骨外髁上4cm、桡神经沟处2点面积依次为(x珋±S)5.14±1.24 mm2、5.08±1.23mm2。左右上肢之间同一测量点比较神经横截面积P>0.05,桡神经的CSAs同年龄组男女之间比较P<0.05,桡神经在青、中、老三组CSA相比P>0.05。桡神经横截面积与身高、体重呈正相关性。桡神经横截面积与体重的最大相关系数是0.36(P<0.01),与身高的最大相关性系数是0.38(P<0.01)。结论桡神经在不同测量点其正常值不同,CSAs在性别对比中存在差异,青、中、老三组对比CSAs无差异,身高、体重与神经的大小呈正相关性。     

Median and ulnar nerve conduction studies among workers: Normative values

To determine normative values for nerve conduction studies among workers, we selected a subset of 326 workers from 955 subjects who participated in medical surveys in the workplace. The reference cohort was composed exclusively of active workers, in contrast to the typical convenience samples. Nerve conduction measures included bilateral median and ulnar sensory amplitude and latency (onset and peak). Workers with upper extremity symptoms, medical conditions that could adversely affect peripheral nerve function, low hand temperature, or highly repetitive jobs were excluded from the “normal” cohort. Linear regression models explained between 21% and 51% of the variance in nerve function, with covariates of age, sex, hand temperature, and anthropometric factors. The most robust models were fitted for sensory amplitudes in the median and ulnar nerves for dominant and nondominant hands. The median–ulnar difference was least sensitive to adjustment, indicating it is the best measure to use if corrections are not made to account for relevant covariates. A key point was that the magnitude of variance increased with age and anthropometric factors. These findings provide strong evidence that to improve diagnostic accuracy, electrodiagnostic testing should control for relevant covariates, particularly age, sex, hand temperature, and anthropometric factors. © 1998 John Wiley & Sons, Inc. Muscle Nerve 21:999–1005, 1998.     

Ultrasonographic measurement of median nerve cross-sectional area in idiopathic carpal tunnel syndrome: Diagnostic accuracy

Severity-correlated enlargement of the median nerve occurs in idiopathic carpal tunnel syndrome (CTS). We determined whether measurement of the nerve cross-sectional area was useful in making the diagnosis of CTS. In 414 wrists of 275 patients with clinically diagnosed idiopathic CTS and 408 wrists of 408 controls, we made ultrasonographic measurements of the nerve area at the distal (distal edge of the flexor retinaculum), mid (hook of the hamate), and proximal carpal tunnel (wrist crease). Criteria based on the area at a single level yielded sensitivities of 43-57% and specificities of 96-97%. Use of the mean carpal nerve area (average of the areas at the three levels) improved the results (sensitivity, 67%; specificity, 97%), which was as sensitive as the nerve conduction studies (NCS). In the NCS, we obtained sensitivities of 66% for the distal motor nerve latency and 67% for the distal sensory nerve latency, with specificities of 97% for each. A combination of the mean carpal nerve area and NCS criteria yielded a sensitivity of 84% and a specificity of 94%. The clinical implications of these findings for the diagnosis of CTS are discussed.     

Evidence-based guideline: neuromuscular ultrasound for the diagnosis of carpal tunnel syndrome

Introduction: The purpose of this study was to develop an evidence‐based guideline for the use of neuromuscular ultrasound in the diagnosis of carpal tunnel syndrome (CTS). Methods: Two questions were asked: (1) What is the accuracy of median nerve cross‐sectional area enlargement as measured with ultrasound for the diagnosis of CTS? (2) What added value, if any, does neuromuscular ultrasound provide over electrodiagnostic studies alone for the diagnosis of CTS? A systematic review was performed, and studies were classified according to American Academy of Neurology criteria for rating articles of diagnostic accuracy (question 1) and for screening articles (question 2). Results: Neuromuscular ultrasound measurement of median nerve cross‐sectional area at the wrist is accurate and may be offered as a diagnostic test for CTS (Level A). Neuromuscular ultrasound probably adds value to electrodiagnostic studies when diagnosing CTS and should be considered in screening for structural abnormalities at the wrist in those with CTS (Level B). Muscle Nerve 46: 287–293, 2012     

Ultrasound therapy facilitates the recovery of acute pressure-induced conduction block of the median nerve in rabbits

Though the use of ultrasound for the treatment of carpal tunnel syndrome (CTS) or compression neuropathy has been described, its effect remains controversial. A test model of acute CTS was developed using rabbits. Acute median nerve compression was induced by the infusion of saline into the carpal tunnel under general anesthesia to elevate the intracarpal pressure. A reduction in the compound muscle action potential (CMAP) amplitude of the abductor pollicis was noted after intracarpal pressure increased. To investigate the efficacy of ultrasound in acute CTS, rabbits with acute median nerve compression were divided into 3 groups (10 each) and ultrasound was applied at different intensities to each group as follows: 1.5 W/cm(2) to group 1; 0.2 W/cm(2) to group 2; 0.0 W/cm(2) (sham) to group 3. A total of 10 treatment sessions were given over a period of 2 weeks. Following ultrasound application, the CMAP amplitudes showed significant improvement in group 1 compared to the other two groups (P < 0.05), indicating facilitated recovery from acute CTS in this pressure-induced median nerve compression rabbit model. The benefits of ultrasound application in a clinical setting must be verified by further clinical trials.     

Relating applied strain to the type and severity of structural damage in the rat median nerve using second harmonic generation microscopy

Introduction: The objective of this study was to determine if the presence or absence of a palmaris longis tendon influenced the function of the median nerve across the wrist. The primary hypothesis was that the presence of a palmaris longus tendon would be associated with more median nerve entrapment at the wrist. Methods: This was a cross‐sectional study. Subjects were recruited at a screening of dental professionals. The median and ulnar sensory nerve latencies across the wrist (relative prolongation of the median compared with the ulnar) and the presence or absence of the palmaris longus tendon were the primary outcome measures. Results: A total of 462 subjects were recruited into the study of which 16.2% lacked a palmaris longus tendon. There was no difference in the median nerve function or the percentage with a 0.5 ms prolongation of the median sensory latency when comparing subjects with and without a palmaris longus tendon. Conclusions: The presence of a palmaris longus tendon does not influence the median nerve function across the wrist. Muscle Nerve 45: 895–896, 2012     

A very large Schwannoma originating from the median nerve in carpal tunnel

Schwannomas are common benign nerve tumors occurring in the peripheral nerves. A very large schwannoma of more than 5 years duration, originating from the median nerve in the carpal tunnel in a 38-year-old woman, is reported. There was a painful mass, 60 mm in length and 42 mm in diameter, on the palm without signs of sensory disturbance or atrophy on the thenar muscles. Surgical removal was performed under high-power magnification by separating the sensory and motor fascicles from the tumor. Histological examination resulted in a Schwannoma. At 4-year follow-up, the patient was asymptomatic with excellent relief of symptoms. The tumor did not recur. Although cases have been reported in the literature, this is one of the largest ever described without any neurologic deficit.     

Median nerve changes following steroid injection for carpal tunnel syndrome

Introduction: Neuromuscular ultrasound is a painless, radiation‐free, high‐resolution imaging modality for assessment of the peripheral nervous system. The purpose of this study was to use neuromuscular ultrasound to assess the changes that occur in the median nerve after steroid injection for carpal tunnel syndrome (CTS). Methods: Ultrasound and nerve conduction studies were performed at baseline and 1 week, 1 month, and 6 months after steroid injection in 19 individuals (29 wrists) with CTS. Results: Significant changes were noted in median nerve cross‐sectional area (P < 0.001), mobility (P = 0.001), and vascularity (P = 0.042) at the distal wrist crease after steroid injection, and the nerve cross‐sectional area correlated with symptom score and electrodiagnostic parameters. Changes in the ultrasonographic parameters were seen within 1 week of injection. Conclusions: These findings suggest neuromuscular ultrasound is potentially helpful for the assessment of individuals undergoing treatment for CTS, as typical changes can be expected after successful treatment injection. Muscle Nerve 44: 25–29, 2011