Clinical and electrodiagnostic evaluations of peripheral nerves are widely used nowadays to assess the severity of trauma to the peripheral nerves. However, a major limitation is that these approaches are not able to determine the extent of damage to the nerve fibers in the first 6 weeks post trauma(1). Another disadvantage is that CT and MRI scans for neurographic studies are not always readily available and prove to be costly. High-resolution ultrasonography, on the other hand, is a dynamic, portable and cost-effective modality for the assessment of the peripheral nerves.
On ultrasound, the peripheral nerves show a tape-like fibrillar pattern on longitudinal scans and an ovoid fibrillar pattern on transverse scans. These specific patterns with a characteristic echotexture on sonography can be well correlated with the normal histology of the nerves(2).
The radial nerve is more commonly involved in entrapment syndromes compared to other peripheral nerves of the upper limb, such as the median or ulnar nerve. Common sites of nerve entrapment are the junction of the middle and distal third of the arm (post traumatic), just distal to the elbow (arcade of Frohse), and proximal to the wrist between the brachioradialis and the extensor carpi radialis longus(3). Generally, it is difficult to diagnose the condition clinically, and the final diagnosis is mostly obtained by excluding other differentials. This can lead to a delay in the initiation of effective treatment(3).
Studies show that high-resolution ultrasonography is useful for the localization of trauma, entrapment neuropathies, and infectious conditions and neoplasms involving the peripheral nerves(4–6).
The present study seeks to obtain high-resolution sonographic images of normal radial nerves to assess potential relationships between the CSA and the age, gender, height, weight, body mass index (BMI), and hand dominance of the subjects.
The study was conducted on 200 subjects. Individuals of both sexes, between 18 and 75 years of age, not having any history of peripheral neuropathy or trauma to the upper limb, and referred to the department of radiodiagnosis and imaging of the Sri Guru Ram Das Institute of Medical Sciences and Research, Sri Amritsar, for other medical or surgical conditions, were included in the study. Ethical clearance for the study was granted by the ethics committee at the Sri Guru Ram Das Institute of Medical Sciences and Research (reference number: Patho190/19).
Patients showing features of peripheral neuropathy as a result of trauma, pregnancy, diabetes mellitus, hypothyroidism or alcoholism were excluded from the study. After obtaining informed written consent from each subject, detailed clinical history was recorded, and high-resolution ultrasonography of the radial nerve was performed in both arms.
High-resolution sonography was performed using Philips Affiniti 50 ultrasound unit with a linear transducer having a frequency range of 5–18 Mhz. The depth, gain, and dynamic range were adjusted for better characterization between the radial nerve and adjacent soft tissues. The sonographic images were obtained with the subject in supine position. The sonographic images were recorded by placing the transducer probe perpendicular to the normal radial nerve. The reference values for the CSA of the nerve at two levels were measured by the ultrasonographer in 200 subjects. At each level, the CSA of the radial nerve was calculated by circumferentially tracing the inner side of the peripheral hyperechoic rim of the nerve. The pressure of the transducer on the skin was kept to a minimum to reduce as far as possible the deformation of the underlying structures. A few studies have demonstrated the use of standard imaging as well as write-zoom magnification methods for measurement of the CSA. In the present study, we used only standard imaging.
The CSA were measured in the following locations: the radial nerve 2 cm proximal to its bifurcation into the superficial sensory nerve and the posterior interosseous nerve (level 1) (Fig. 1, Fig. 2), and the radial nerve in the anterior compartment just after it exits the spiral groove (level 2) (Fig. 3, Fig. 4).The CSA value was measured three times at the same level, and the mean was then calculated at each level (Fig. 5, Fig. 6, Fig. 7, Fig. 8, Fig. 9, Fig. 10, Fig. 11, Fig. 12). Age, gender, height, weight body mass index and hand dominance obtained from each subject were documented. The correlation coefficients were calculated by statistically correlating these parameters with the cross-sectional area of the radial nerve at both levels.
The data was analyzed using SPSS 24.0 software. Qualitative variables (sex, hand dominance) as well as quantitative variables (CSA, BMI, age, height, weight) were evaluated in the study. The means as well as standard deviations for the CSA of the radial nerves were calculated at two levels in bilateral upper arms in both men and women. Independent sample t-test was used to evaluate the association between the qualitative (gender and hand dominance) and quantitative (CSA) variables. The correlation of the mean CSA of the radial nerves with age, height, weight, and body mass index (BMI) was done using Pearson’s correlation analysis (‘r’ value).
The mean CSA of the radial nerves calculated at level 1 and level were 2.3 ± 0.3 mm2 and 4.3 ± 0.4 mm2, respectively. There was a considerable difference in the mean CSA calculated at both these levels (
Mean cross-sectional area (cm2) of the radial nerves at levels 1 and 2
Level | CSA | |
---|---|---|
Mean | SD | |
|
0.023 | 0.003 |
|
0.043 | 0.004 |
|
0.001 |
CSA – cross-sectional area, SD – standard deviation
Men had a significantly larger mean CSA than women (
Mean cross-sectional area (cm2) of both radial nerves at two levels, and their relationship with patient sex
Sex | No. of cases | CSA level 1 | |||||
---|---|---|---|---|---|---|---|
Right |
|
Left |
|
||||
Mean | SD | Mean | SD | ||||
|
105 | 0.02443 | 0.003037 |
|
0.02494 | 0.008413 |
|
|
95 | 0.02104 | 0.003058 | 0.02142 | 0.005664 |
Gender | No. of cases | CSA level 2 | |||||
---|---|---|---|---|---|---|---|
Right |
|
Left |
|
||||
Mean | SD | Mean | SD | ||||
|
105 | 0.04496 | 0.003611 |
|
0.04538 | 0.013641 |
|
|
95 | 0.04095 | 0.003512 | 0.04072 | 0.003102 |
CSA – cross-sectional area, SD – standard deviation
Cross-sectional area (cm2) of the radial nerve at two levels, and its relationship with the dominant and non-dominant sides
Dominant side | No. of cases | CSA level 1 | |||||
---|---|---|---|---|---|---|---|
Right |
|
Left |
|
||||
Mean | SD | Mean | SD | ||||
|
11 | 0.02342 | 0.002244 |
|
0.02389 | 0.002424 |
|
|
189 | 0.02279 | 0.003535 | 0.02324 | 0.007624 |
Dominant side | No. of cases | CSA level 1 | |||||
---|---|---|---|---|---|---|---|
Right |
|
Left |
|
||||
Mean | SD | Mean | SD | ||||
|
11 | 0.04400 | 0.002324 |
|
0.04376 | 0.002237 |
|
|
189 | 0.04297 | 0.004165 | 0.04313 | 0.010640 |
CSA – cross-sectional area, SD – standard deviation
The mean CSA of the radial nerves at both levels in bilateral arms showed a significant (
Cross-sectional area (cm2) of the radial nerve at two levels, and its relationship with height
Height | No. of cases | CSA level 1 | |||||
---|---|---|---|---|---|---|---|
Right |
|
Left |
|
||||
Mean | SD | Mean | SD | ||||
|
54 | 0.01935 | 0.002298 |
|
0.02017 | 0.006965 |
|
|
110 | 0.02315 | 0.002379 | 0.02310 | 0.002869 | ||
|
36 | 0.02705 | 0.002451 | 0.02844 | 0.013136 |
Height | No. of cases | CSA level 1 | |||||
---|---|---|---|---|---|---|---|
Right |
|
Left |
|
||||
Mean | SD | Mean | SD | ||||
|
54 | 0.03917 | 0.002684 |
|
0.03914 | 0.002340 |
|
|
110 | 0.04489 | 0.013782 | 0.04419 | 0.013138 | ||
|
36 | 0.04714 | 0.004031 | 0.04606 | 0.005176 |
CSA – cross-sectional area, SD – standard deviation
Cross-sectional area (cm2) of the radial nerve at two levels, and its relationship with weight
Weight (kg) | No. of cases | CSA level 1 | |||||
---|---|---|---|---|---|---|---|
Right |
|
Left |
|
||||
Mean | SD | Mean | SD | ||||
|
49 | 0.01931 | 0.002597 |
|
0.02025 | 0.007380 |
|
|
90 | 0.02251 | 0.002163 | 0.02335 | 0.009055 | ||
|
61 | 0.02610 | 0.002596 | 0.02557 | 0.002272 |
Weight (kg) | No. of cases | CSA level 1 | |||||
---|---|---|---|---|---|---|---|
Right |
|
Left |
|
||||
Mean | SD | Mean | SD | ||||
|
49 | 0.03916 | 0.003223 |
|
0.03913 | 0.002741 |
|
|
90 | 0.04451 | 0.015217 | 0.04359 | 0.014653 | ||
|
61 | 0.04632 | 0.003528 | 0.04578 | 0.003263 |
CSA – cross-sectional area, SD – standard deviation
Cross-sectional area (cm2) of the radial nerve at two levels, and its relationship with body mass index
BMI | No. of cases | CSA level 1 | |||||
---|---|---|---|---|---|---|---|
Right |
|
Left |
|
||||
Mean | SD | Mean | SD | ||||
|
63 | 0.02108 | 0.003902 |
|
0.02289 | 0.012558 |
|
|
61 | 0.02294 | 0.002996 | 0.02286 | 0.003150 | ||
|
76 | 0.02417 | 0.002830 | 0.02392 | 0.002755 |
BMI | No. of cases | CSA level 1 | |||||
---|---|---|---|---|---|---|---|
Right |
|
Left |
|
||||
Mean | SD | Mean | SD | ||||
|
63 | 0.04348 | 0.018645 |
|
0.04087 | 0.003869 |
|
|
61 | 0.04311 | 0.003775 | 0.04450 | 0.017814 | ||
|
76 | 0.04450 | 0.003392 | 0.04400 | 0.003420 |
CSA – cross-sectional area, SD – standard deviation
Cross-sectional area (cm2) of the radial nerve at two levels, and its relationship with age
Age group (years) | No. of cases | CSA level 1 | |||||
---|---|---|---|---|---|---|---|
Right |
|
Left |
|
||||
Mean | SD | Mean | SD | ||||
|
51 | 0.02214 | 0.003787 |
|
0.02257 | 0.012087 |
|
|
79 | 0.02237 | 0.002928 | 0.02271 | 0.003159 | ||
|
70 | 0.02317 | 0.003633 | 0.02410 | 0.006411 |
Age group (years) | No. of cases | CSA level 1 | |||||
---|---|---|---|---|---|---|---|
Right |
|
Left |
|
||||
Mean | SD | Mean | SD | ||||
|
51 | 0.04179 | 0.004172 |
|
0.04158 | 0.003892 |
|
|
79 | 0.04409 | 0.004461 | 0.04350 | 0.004013 | ||
|
70 | 0.04473 | 0.016338 | 0.04390 | 0.015726 |
CSA – cross-sectional area, SD – standard deviation
High-resolution ultrasonography is a newly evolving tool to evaluate disorders of the peripheral nervous system(7). The ultrasound appearance of a normal peripheral nerve shows multiple hypoechoic longitudinal nerve fascicles which are separated by discontinuous echogenic bands corresponding to the epineurium(8–11). A previous study done by Alshami
The mean CSA values in our present study were 2.3 ± 0.3 mm2 and 4.3 ± 0.4 mm2 at levels 1 and 2, respectively (Tab. 1). The CSA of the nerve varies along its course in the arm, with the nerve being thicker in the proximal part and having a greater CSA. In a study conducted by Chen
Bedewi
Chen
High-resolution ultrasonographic evaluation of the peripheral nerves allows good depiction of nerve morphology and can identify pathological changes such as nerve enlargement and alterations in the echopattern(24–26). Ultrasound also provides useful information about the morphology, precise location, and anatomical course of the nerve(27). The CSA values of the radial nerve obtained in this study will establish the normal range of values, which can facilitate the diagnosis of abnormal nerve disorders such as neuropathies, trauma, tumors, and entrapment involving the nerve. All these disorders will cause a significant alteration in the CSA of the radial nerve from the normal range of values(28,29).
There are a few limitations associated with the present study. The sample population was restricted to one demographic area, and the CSA measurements were done only at two levels. Including a population from different demographic strata and taking CSA measurements at more levels could be performed to avoid these limitations.
The mean CSA in our present study was 2.3 ± 0.3 mm2 and 4.3 ± 0.4 mm2 at levels 1 and 2, respectively. Healthy subjects showed a strong correlation between the CSA of the radial nerve and height, weight, BMI, and but no correlation with age. Males had larger CSA values of the radial nerve than females. We can practically compare both dominant and non-dominant hands, as there was no statistical difference between the CSA of the radial nerves in the dominant and non-dominant hands. These normal reference values of the radial nerve can facilitate the study of sex-specific differences, and provide information on side to side variations along with abnormal nerve conditions. Hence, these ultrasonographic reference values along with basic clinical data will aid in the diagnosis, response to treatment, and prognostic evaluation of peripheral neuropathies.