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St. Elisabeth Hospital 5000 LC Tilburg, The Netherlands
In the August 2001 issue of the American Journal of Roentgenology, we read with interest an article by Peer et al. [1] about high-resolution sonography in patients with postoperative peripheral nerve lesions. At our department of neurology, we are becoming increasingly interested in this mode of investigation of the peripheral nervous system, especially because advances in sonographic technology such as higher spatial resolution have made it possible to depict the nerve itself.
Peer et al. [1] have described sonographic findings in 18 patients with postoperative peripheral nerve damage. In eight patients, the nerve lesion was primarily caused by direct nerve surgery, including exploration, nerve repair, and decompression. In 10 patients, the lesion developed as a result of operations that did not directly involve the nerve (i.e., orthopedic surgery or open biopsy). Aside from possible compressive structures, nerve thickening was one of the major sonopathologic features the authors found in their patients.
We agree that nerve thickening found at sonography may have a localizing value in peripheral nerve lesions, but we would emphasize that this feature is not found exclusively in postoperative patients. Nerve thickening may also be seen in patients with neuropathies that are not operated on. In fact, several studies (some of which were already cited by the authors in their article) have shown that nerve thickening found at sonography may be diagnostic for an entrapment neuropathy, as in carpal tunnel syndrome [2] or ulnar neuropathy at the elbow [3, 4]. In a pilot study we conducted in 24 patients with ulnar neuropathy at the elbow, thickening of the nerve appeared to be a highly sensitive and specific sonographic sign for the diagnosis of ulnar neuropathy at the elbow [4].
From the information presented [1] on the eight patients whose injury was related to nerve surgery, it is not known whether nerve thickening already existed before the operation. The patients were not sonographically examined before the operation. In other words, it is not certain—and may even be unlikely—that the nerve thickening found after surgery was caused by the operation itself. This point is particularly important when, as stated by the authors in their introduction, medical—legal questions and decisions about possible treatment are related to the sonographic test result. However, to our knowledge, no systematic follow-up studies are available yet in which the preoperative and postoperative sonographic features are compared in patients with entrapment neuropathies.
References
University Hospital Innsbruck A-6020 Innsbruck, Austria
We appreciate the interest in our work by Beekman et al. They correctly state that thickening of a peripheral nerve is not an exclusive feature of postoperative nerve lesions, and we certainly did not state that in our article [1]. They add (and relate the statement to our description of eight patients with nerve injury after having nerve surgery) that the decision about possible treatment in patients with injury related to nerve surgery may not, therefore, be based on sonographic findings, because one cannot be sure that postoperative swelling of a nerve is caused by the surgical procedure.
Not all eight, but only four of our patients with injury related to nerve surgery merely had thickening of the nerve after the operation. In the detailed description of our results [1], we stated that two patients had undergone primary nerve repair after trauma; in these patients, insufficient repair with only partly adapted fascicles was shown. An encasing scar was shown in two patients: in one patient, it was seen after decompression of Guyons canal (figure 7 in our article) and in the other, after decompression of the ulnar sulcus (figure 2B in our article).
The finding of a thickened nerve after nerve surgery alone is a notable finding but, per se, does not imply anything except a thickened nerve. The importance of the sonographic examination lies in the search for an underlying reason this thickening exists, such as scar formation or compression by a hematoma. Although nobody would advocate surgical exploration of a nerve that merely appears to be thickened after an operation (and neither did we), exploration may often be recommended in the case of coexisting abnormality, as shown in our data.
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