The Utility of Ultrasound in the Assessment of Traumatic Peripheral Nerve Lesions: Report of 4 Cases

Joshua Zeidenberg, MD; S. Shelby Burks, MD; Jean Jose, DO; Ty K. Subhawong, MD; Allan D. Levi, MD, PhD

Disclosures

Neurosurg Focus. 2015;39(3):e3 

In This Article

Discussion

Over half of all peripheral nerve injuries in the setting of trauma require surgical intervention.[20] The precise localization of the site and extent of injury may remain uncertain after physical examination and EMG testing.[24] Ultrasound has been shown to be an efficient, noninvasive, and low-cost method of imaging traumatic peripheral nerve pathologies.[9,10,16,21,22,24,26] After trauma, HRU can differentiate between rupture of a nerve bundle and fibroblast infiltration, which results in the formation of a traumatic neuroma.[24] Padua et al.[21] showed that ultrasound was able to aid in the diagnosis or modification of the therapeutic path in 60% of patients with traumatic nerve lesions and, most importantly, in the diagnosis of axonotmesis/neurotmesis when neurophysiological evaluation could not.

In Case 1, we were able to accurately diagnose both tibial and, previously unrecognized, peroneal nerve transections with end-bulb neuromas using HRU in a patient who suffered a devastating leg injury. In addition, HRU showed the precise level of injury at the bifurcation of the sciatic nerve. The anatomical detail and extent of injury shown on HRU images matched the findings from MRI, but HRU showed the anatomy of individual fascicles and demonstrated a clear border between normal and abnormal tissue when MRI could not (Fig. 2). In a prospective study of 22 patients with lower-extremity nerve injuries, Cokluk and Aydin[10] concluded that visualization of lowerextremity peripheral nerves using ultrasound was good or excellent in 95% of the cases.[10] In addition, these authors were able to visualize and diagnosis stump neuromas in nearly 80% of the cases with only a 5-MHz probe.[10]

Case 2 showed iatrogenic pseudoaneurysm formation in a patient after a cardiac catheterization procedure, which displaced and dissected into the left femoral nerve. Although MRI accurately showed the femoral nerve involvement and the adjacent signal abnormality from the pseudoaneurysm, the femoral profunda pseudoaneurysm was shown more clearly on ultrasound using color Doppler imaging, and the displacement and dissection of the femoral nerve were clearly displayed. Although there are case reports in the literature describing peripheral nerve injury caused by pseudoaneurysms, there have been no large-scale studies evaluating the ability of ultrasound to identify and assess these lesions accurately.[7,17] We believe that neuronal damage secondary to vascular malformations can be well assessed with HRU, and further study is warranted.

Case 3 describes an ulnar nerve lesion for which ultrasound was used not only to confirm failure of the original graft but also to follow-up the integrity of the subsequent sural nerve-grafting procedure (Fig. 7C). Although ultrasound cannot detect peripheral nerve regeneration physiologically, the anatomical continuity of the nerve-grafting procedure can be confirmed. To our knowledge, no studies to date have critically evaluated the ability of ultrasound to assess graft integrity after surgical repair of a nerve gap. In general, ultrasound has been very effective in characterizing ulnar nerve pathology. In a prospective study of 91 patients with ulnar neuropathy, Filippou et al.[11] showed HRU to successfully reveal detailed anatomy of the ulnar nerve. They also demonstrated the ability of HRU to distinguish several etiologies of ulnar neuropathy such as subluxation and the presence of osteophytes and osseous lesions, articular ganglia, and posttraumatic lesions.[11] A separate study by Ng et al.[19] found that HRU is of greater use than nerve-conduction studies in the localization of ulnar neuropathy both at the elbow and outside the elbow in cases of traumatic ulnar neuropathy. Thus, HRU can accurately evaluate the relationship of the ulnar nerve with the adjacent soft tissues and osseous structures by using dynamic maneuvers without sacrificing excellent definition of the nerve and surrounding structures.[11] In our case, the ultrasound images clearly showed contiguous and well-positioned sural grafts after nerve-gap repair (Fig. 7C). We believe that HRU would be a valuable tool in the postoperative stage, and this is an interesting topic for further research.

Case 4 describes the case of a woman who suffered a Sunderland Grade 5 injury to her spinal accessory nerve after surgical excision of a schwannoma. HRU clearly showed the accessory nerve transection and an end-bulb neuroma (Fig. 8). Bodner et al.[6] described 4 cases of patients with accessory nerve palsy diagnosed directly or indirectly by trapezius muscle atrophy. Accessory nerve palsy causes dysfunction, weakness, and pain of the muscle, and the patient may present with a dropping shoulder or winged scapula on examination.[6] The most common cause of accessory nerve injury is iatrogenic, for example with tumor resection or biopsy (as seen in our case), lymph node biopsy, or carotid endarterectomy.[13,25] A review of the literature revealed that the use of HRU in diagnosing accessory nerve injuries has not been well studied.

Ordering physicians should be aware of the limitations inherent to the sonographic assessment of peripheral nerves. Ultrasound is operator dependent and requires knowledge of anatomy and subtle sonographic findings that involve structures that are only a few millimeters in size. With a linear-array transducer of < 7 MHz, the resolution is inherently limited in deeper tissues, particularly when the nerve lies deeper than 3 cm.[24] This limitation can be overcome in areas such as the supraclavicular brachial plexus, as demonstrated by Gruber et al.,[12] by using more powerful broadband linear-array transducers. Subtle abnormalities in deeper nerves may be harder to assess than with MRI, in which there is only signal abnormality but no change in nerve caliber. Finally, in our experience, changes in the surrounding muscle, such as subtle denervation edema or fatty atrophy, may be more difficult to appreciate with ultrasound than with MRI.

Ultrasound is becoming an increasingly important part of the diagnostic evaluation of peripheral nerve injuries despite the aforementioned limitations, and there are several well-described examples in the literature indicating that ultrasound may be the preferred imaging modality for assessing peripheral nerve lesions. High-frequency ultrasound can detect tiny abnormalities that simply cannot be shown by standard clinical MRI techniques, because the axial resolution is much better than is currently achievable with clinical MRI scanners. The axial resolution of a 10-MHz probe is approximately 150 μm, much better than is currently achievable with clinical MRI scanners.[18] In our experience, ultrasound is better able to delineate the tiny fascicles in the ulnar (Fig. 7C) spinal accessory nerves (Fig. 8A), which are difficult to discern on MRI. MRI is relatively contraindicated in patients with cardiac pacemakers and certain metal implants, and many patients find long MRI examinations uncomfortable because of claustrophobia or pain caused by immobilization.[2] There are no contraindications for ultrasound examination. HRU also offers the benefit of dynamic imaging, which can show real-time changes, such as ulnar nerve subluxation during elbow flexion.[14] Ultrasound also offers a more flexible field of view, an advantage over MRI when evaluating structures that have a long course in the body, such as peripheral nerves.[18] Sonography also may be preferred over MRI when there is surgical hardware adjacent to the site of nerve injury, because it is not hampered by metallic artifacts.[18]

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