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Clinical Observations |
1 Department of Pediatrics, University of Tuebingen, Hoppe-Seyler-Str. 1,
D-72076 Tuebingen, Germany.
2 Department of Hand-, Plastic-, and Reconstructive Surgery with Burn Unit,
BG-Trauma Centre, University of Tuebingen, Tuebingen, Germany.
Received December 7, 2004;
accepted after revision May 19, 2005.
Address correspondence to H. P. Haber
(peter.haber{at}med.uni-tuebingen.de).
Abstract
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CONCLUSION. Sonography of the brachial plexus was technically feasible, although the entire brachial plexus could not be evaluated. Sonography appears to be a useful bedside imaging technique for assessing brachial plexus injury. The potential of sonography as a complementary diagnostic tool in the evaluation of these patients warrants further investigation.
Keywords: emergency radiology • head and neck imaging • injury • neuroimaging • sonography • trauma
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Improvements in sonographic technology have enabled visualization of the brachial plexus in healthy subjects [5-7]. Although sonography has been used for imaging of peripheral nerve abnormalities [8, 9], to our knowledge only one report of its use in the evaluation of patients with a brachial plexus lesion [10] has been published. The authors described the sonographic findings of a brachial plexus injury after extirpation of a suspected enlarged supraclavicular lymph node. We present four patients with traction injury of the brachial plexus for whom sonography contributed useful information toward establishing the extent of the lesion.
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Sonographic imaging was performed before the operation using a Sonoline Elegra Advanced scanner (Siemens Medical Solutions) with a 13-MHz linear array transducer.
The patients were examined in a semilateral decubitus position without specific preparation. Coronal oblique planes (Fig. 1A) were used to identify the transverse processes of the vertebrae as hyperechoic bone prominences with posterior acoustic shadowing. In the groove between the transverse processes, the hypoechoic nerve roots were visualized as they left the intervertebral foramina in a downward direction (Fig. 1B). When the hypoechoic roots between the transverse processes were absent, the lesion was classified as an avulsion.
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The level of individual roots was identified on the basis of the different morphology of the cervical transverse processes of the vertebrae: The anterior tubercle of the transverse process is selectively absent in the C7 vertebra [11]. The root levels of the upper vertebrae could be identified by counting the number of transverse processes encountered while sweeping the transducer cranially from C7.
All sonographic images were obtained and interpreted by one sonologist, who has more than 15 years of experience in diagnostic sonography. The investigator was unaware of the clinical findings. The sonographic findings and the level of abnormality were recorded in a medical report. The sonographic examination took 30-45 min for each patient.
Three senior staff surgeons with added qualifications in traumatic nerve injury surgery performed the surgery using standard areas of exploration. The surgeons were aware of the sonographic findings before exploration. The results of the sonographic imaging were compared with the operative findings for each nerve root.
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In our experience, the cervical part of the brachial plexus was best visualized on coronal oblique planes showing the hypoechoic roots in longitudinal sections as they exit the neural foramina (Fig. 1A, 1B). In the supra- and infraclavicular regions, we found that an axial oblique plane running parallel to the subclavian artery was the most reliable for an accurate depiction of the pathologic lesions.
Table 1 summarizes both the sonographic and operative findings. Sonographic examination allowed visualization of C5-C7 levels in all patients. However, C8 level was not detected in three patients. Sonography depicted all avulsions of nerve roots C5-C7 (Fig. 2A, 2B and 2C).
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In one patient, the nerves appeared as hyperechoic structures, in contrast to the healthy hypoechoic fascicular pattern (Fig. 3). In these patients, it was difficult to follow the roots in a longitudinal plane because of the relatively echogenic surrounding structures. On subsequent surgery, extensive scar tissue formation was seen and, at the level of the scar itself, the nerve roots were indistinguishable from the scar tissue.
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MRI is currently the technique of choice for imaging the brachial plexus [3, 4], but the complexity of the brachial plexus and changing orientation of the nerves as they descend make identification of individual structures difficult [4]. In addition, MRI is expensive, time consuming, and not readily available.
Sonography overcomes these limitations. This imaging technique in experienced hands is noninvasive, relatively inexpensive, and quick to perform, giving it distinct advantages over MRI.
This study specifically focused on the feasibility of imaging the brachial plexus with sonography in patients with traction injury. Using a high-resolution 13-MHz transducer, this technique allowed us to visualize healthy nerve structures and root avulsion or nerve injury in the form of neuroma and scar tissue formation. However, a careful technique must be used to differentiate nerve structures from surrounding organs and structures. Many structures of similar echoic appearance, such as muscle fascicles and vessels, course in the same plane, and correct differentiation among them can be difficult. Thus, sonography of the brachial plexus requires experienced hands and a good grounding in anatomy.
In our experience, a coronal oblique plane was the most reliable for the accurate depiction of the avulsion of the cervical nerve roots. In this region, the healthy nerve roots appeared as well-delineated hypoechoic structures as they left the intervertebral foramina in a caudal and lateral direction. Using this coronal oblique plane, all avulsions were correctly identified by showing empty neural foramina. However, the technique was limited by the fact that we could not show the attachment of the nerve rootlets to the spinal cord because of shadowing from bone. As a result, isolated intradural damage was not immediately obvious on sonographic imaging of the plexus, as reported with MRI [4].
Sonographic examination of the brachial plexus may reveal scarring, providing clear evidence of injury at this level. In our patient, the nerve was surrounded by echogenic soft tissue, and at the level of the scar itself, the nerve was indistinguishable from the scar tissue. Therefore, it may be difficult to show the continuity of the nerve at this level, as reported by Peer et al. [9].
On the sonographic scans, the neuroma appeared as a discrete hypoechoic fusiform mass consisting of multiple longitudinal hypoechoic bands separated by hyperechoic tissue. The operative finding showed formation of the neuroma involving the three intact cords of the brachial plexus. This finding resembles the description of spindle neuroma occurring in intact nerves caused by chronic irritation [8]. By contrast, peripheral nerve lesions after surgery are described as being more hypoechoic, and fascicular structure is not as well shown [9]. These terminal neuromas arise in the course of surgery at the proximal nerve end of the nerve itself, such as complete transection of a nerve in the limb after surgical amputation. Further studies are necessary to establish the exact morphologic correlate of posttraumatic neuroma of the brachial plexus on sonography.
Another limitation of this technique is the difficulty of visualizing the C8 and T1 nerve roots. These levels are too caudal and deep, especially in subjects with thick, short necks, and therefore are harder to scan. The difficulty in assessing the C8 and T1 nerve roots has also been reported with MRI [3]. Because the entire brachial plexus cannot be visualized with sonography, each study needs to be tailored on the basis of the clinical and prior imaging findings.
Several additional limitations apply to our study. These include the small sample size (n = 4) and institutional patient-selection bias. Further work in series of patients with brachial plexus injury is necessary to determine the sensitivity and specificity of this method.
Advances in sonographic imaging technology have enabled acquisition of 3D sonography data sets [12]. Multiplanar reconstruction of the data may help delineate the complex morphology of the brachial plexus at several levels. This should be particularly useful in the evaluation of the lower trunk, to improve accuracy in diagnosing lesions of nerve roots C8 and T1. The technique of 3D sonographic imaging appears to be a promising development, but we have so far been unable to perform this type of imaging.
Despite these limitations, sonography appears to be a readily available bedside imaging technique for assessing brachial plexus injury, particularly for use in critically ill patients unable to undergo MRI. This technique may provide additional information for patients whose clinical and neurophysiologic features are inconclusive. Finally, a precise assessment of nerve lesions in neonatal brachial plexus palsy or in primary or secondary tumors may also represent a potential clinical application.
We conclude that sonography of the brachial plexus is technically feasible, although it requires experienced hands and a good grounding in anatomy. Undoubtedly, many features of sonography of the brachial plexus will require further testing before it can become a complementary diagnostic tool. We hope that the results of this preliminary report will motivate others to explore the potential of this technique as an imaging method for this purpose.
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