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Examination of Postoperative Peripheral Nerve Lesions with High-Resolution Sonography

¹ Department of Radiology, University Hospital Innsbruck, Anichstraße 35, A-6020 Innsbruck, Austria.
² Department of Plastic and Reconstructive Surgery, University Hospital Innsbruck and Ludwig Boltzmann Institute of Quality Control in Plastic Surgery, A-6020 Innsbruck, Austria.
³ Department of Neurology, University Hospital Innsbruck, A-6020 Innsbruck, Austria.

Received September 25, 2000; accepted after revision February 9, 2001.

 
Address correspondence to S. Peer.

Abstract

Top Abstract Introduction Subjects and Methods Results Discussion References

 
OBJECTIVE. Peripheral nerve lesions after surgery are common and are related either to direct compromise of the nerve by the surgical procedure (iatrogenic lesions) or to postoperative events such as scar formation. Despite a high sensitivity, electrodiagnosis may not reveal the exact location and cause of a nerve lesion. We hypothesized that high-resolution sonography could be helpful in diagnosing postoperative peripheral nerve lesions by direct visualization of the nerve and surrounding tissues.

SUBJECTS AND METHODS. Eighteen patients with postoperative peripheral nerve lesions that were confirmed with clinical examination and electrodiagnosis were examined on sonography. Eight patients had lesions caused by direct nerve surgery, and 10 patients had undergone a previous orthopedic operation or open biopsy. Sonographic diagnoses were correlated with neurologic examinations and surgical findings.

RESULTS. Reliable visualization of injured nerves on sonography was feasible in all patients. Axonal swelling of a nerve was diagnosed in three patients, direct compromise of a nerve by surrounding scar tissue or surgical implants was diagnosed in 10 patients, a neuroma was diagnosed in three, and insufficient surgical repair, in two. Sonographic findings were confirmed during surgery in all except one patient.

CONCLUSION. In contrast to electrophysiologic tests, high-resolution sonography can show the exact location, extent, and type of a postoperative peripheral nerve lesion and the concurrent disease of surrounding tissues. Because the latter can often be the causative agent for the development of a lesion or the lack of improvement with conservative treatment, sonography yields important information that may not be obtained with other diagnostic modalities.

Introduction

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Peripheral nerve lesions caused by various surgical procedures are common [1,2,3,4]. Some of these lesions may occur during surgical procedures that are not primarily directed towards the nerve itself. Dissection of the nerve, traction, insertion of retractors, or heat are the most common causative agents for this type of injury [4, 5]. Another large group of patients sustains peripheral nerve lesions in the course of surgery of the nerve itself, such as release of a nerve encased in a narrow osteofibrous tunnel or nerve suture after traumatic dissection. In addition, secondary neural damage due to excessive scar formation or compression by hematomas has to be considered. Whereas the former nerve injury is truly iatrogenic, the latter is an unfavorable postoperative result due to naturally occurring complications.

True iatrogenic peripheral nerve lesions are a clinical and medicolegal problem because the causal relationship between medical intervention and the nerve lesion is not easily established. Furthermore, detailed information about the type and extent of neural damage is crucial for the selection of adequate treatment.

The diagnosis of peripheral nerve lesions and the decision regarding surgical or conservative treatment are normally achieved with the aid of clinical and electrodiagnostic tests. Electrodiagnosis may precisely differentiate low-grade lesions without axonal loss (neurapraxia, according to the Sedon and Sunderland classification [6, 7]) from higher grade lesions that have axonal loss and some damage to one or more of the nerve sheath elements (axonotmesis and neurotmesis). Concerning localization of lesions, electromyography and nerve conduction studies are affected by a variety of pitfalls and, therefore, may often not yield reliable information about the precise site of nerve involvement. In the same way, electrodiagnostic tests do not give concise information to aid in making a decision for conservative or surgical therapy. Often a trial of conservative treatment is instituted. If the nerve does not show recovery on follow-up examinations, surgery is performed. Nevertheless, early surgery would be more appropriate even in purely neurapraxic lesions if the nerve is encased by scar tissue, in which case it may not recover with conservative treatment [8]. This diagnosis, however, is beyond the scope of electrodiagnosis and may be accomplished only with direct imaging of the nerve itself. In this regard, high-resolution sonography, which has proven to be efficient in the diagnosis of different types of nerve lesions such as nerve entrapment, nerve tumors, and traumatic nerve lesions [9,10,11,12,13], promises to be a suitable tool for the diagnostic workup of postoperative nerve lesions. The purpose of this study was to assess the value of sonography in determining the presence, localization, and extent of neural damage in patients with clinically suspected postoperative peripheral nerve lesions.

Subjects and Methods

Top Abstract Introduction Subjects and Methods Results Discussion References

 
High-resolution sonography was performed in 18 patients (eight men, 10 women; 21-82 years old) with postoperative peripheral nerve lesions confirmed by clinical examinations and electrodiagnostic tests. Eight patients had nerve lesions caused by direct nerve surgery. An orthopedic operation or open biopsy was performed in 10 patients. Sonography is part of the routine workup in our department and is primarily tailored to look for hematoma at the site of the operation. In a prospective study, this examination was extended to direct investigation of the nerve itself with a high-frequency linear transducer. Eight patients underwent previous surgery with direct exploration of a nerve to perform primary repair of traumatic nerve damage or decompression of a nerve impinged by ligaments or within osteofibrous tunnels. Nine patients underwent orthopedic operations (total hip arthroplasty, arthrodesis, or fracture repair) without direct involvement of a peripheral nerve, but with a possible indirect compromise. In one patient, a percutaneous lymph node biopsy was performed.

High-resolution sonography was performed with an ATL HDI 5000 (Advanced Technology Laboratories, Bothell, WA) with a 5- to 12-MHz broadband linear array probe. Patients were positioned according to the region to be examined. Special care was taken to obtain a stable position of the limb by using supportive cushions, and for the examination of superficial nerves, a gel pad was positioned between the probe and the skin surface. We localized the nerve by using known anatomic landmarks. The examination included the level of suspected damage (in the region of superficial scars) and at least 10 cm above and below this level. The shape, echotexture, diameter, and overall integrity of the nerve and its outer sheath were assessed in the longitudinal and transverse planes and were compared with the nonaffected side. The surrounding soft tissues were screened for the presence of postoperative hematoma or scar tissue. All examinations were performed by two senior staff radiologists with a minimum of 3 years expertise in sonography of small parts. These radiologists diagnosed lesions independently in a prospective manner and were blinded to the results of electrodiagnostic tests. The time to complete the examination of the affected and nonaffected sides was recorded.

In all except one patient who presented with a femoral nerve lesion after total hip arthroplasty and showed good recovery of nerve function with conservative treatment, sonographic findings could be compared with findings at surgical exploration.

Results

Top Abstract Introduction Subjects and Methods Results Discussion References

 
In all 18 patients, transcutaneous high-resolution sonography visualized the involved nerve. In four patients, sonography revealed a thickened nerve with swollen hypoechogenic fascicles suggesting diffuse axonal swelling (Fig. 1A,1B). The outer lining of the nerve was unimpaired, without evidence of discontinuity. Surrounding soft tissues were normal, and no direct impaction of the nerve by scar tissue or hematoma was shown. In seven patients, axonal swelling of the nerve was associated with direct compression of the nerve by encasing scar tissue (Fig. 2A,2B,2C). In one patient who had undergone osteosynthesis of a humeral shaft fracture, direct compression of the radial nerve by the compression plate was shown; the nerve was stretched and diffusely swollen (Fig. 3A,3B). In another patient with humeral fracture repair, a direct compression of the radial nerve by the dislocated fracture and hypertrophic callus formation were seen (Fig. 4). In three patients, a stump neuroma was detected (Fig. 5). In two patients who had received primary repair after traumatic dissection of the ulnar nerve, insufficient repair was shown (Fig. 6). In two patients with a lesion of the accessory nerve, a lymph node biopsy had been performed. On sonography, a neuroma of the accessory nerve was shown in the first patient, and a hypertrophied scar encasing the nerve was shown in the second patient.

View larger version (96K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1A. —57-year-old man after ulnar nerve decompression. Longitudinal sonogram through ulnar nerve shows thickening and markedly edematous swelling of single nerve fascicles but unimpaired perineurium and surrounding soft tissues (arrows).

View larger version (96K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1B. —57-year-old man after ulnar nerve decompression. Longitudinal sonogram of unaffected side shows normal fascicular pattern (arrows).

View larger version (115K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2A. —79-year-old man with persistent pain after ulnar nerve decompression. Longitudinal sonogram through ulnar nerve at level of elbow shows marked edematous swelling of nerve, with hypoechoic fascicles (arrows).

View larger version (120K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2B. —79-year-old man with persistent pain after ulnar nerve decompression. Transverse sonogram shows enlarged diameter of nerve (short arrow) and encasing scar (long arrows).

View larger version (140K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2C. —79-year-old man with persistent pain after ulnar nerve decompression. Operative photograph confirms marked edematous swelling of nerve.

View larger version (136K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3A. —70-year-old woman after repair of humeral shaft fracture. Longitudinal sonogram shows radial nerve stretched across compression plate (short arrow) and markedly swollen (long arrows).

View larger version (137K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3B. —70-year-old woman after repair of humeral shaft fracture. Operative photograph with surgical correlation confirms radial nerve (arrows) stretched alongside compression plate.

View larger version (150K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 4. —20-year-old woman with radial nerve palsy after repair of humeral shaft fracture. Longitudinal sonogram reveals swollen fascicles of radial nerve (short thin arrows) traversing under encasing hypertrophic callus with posterior acoustic shadowing (thick arrow).

View larger version (131K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 5. —55-year-old man after lower leg amputation due to severe arteriosclerotic disease. Longitudinal sonogram shows nerve with globular mass on one end and distal discontinuity consistent with stump neuroma.

View larger version (105K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 6. —18-year-old woman with primary nerve suture after traumatic dissection of ulnar nerve at level of forearm. Longitudinal sonogram shows part of nerve fascicles in normal continuity (long arrows), but gap at surface of nerve, with discontinuity of some nerve fibers. Although continuous fascicles appear normal, there is marked edematous swelling of discontinuous elements (short arrow).

In one patient who had received a release of the distal portion of the ulnar nerve in Guyon's canal, high-resolution sonography showed a small neuroma adjacent to a small overlying scar (Fig. 7A,7B,7C). On subsequent surgical exploration, diffuse swelling of the nerve and compression by the scar was shown, but no neuroma could be found.

View larger version (105K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7A. —Decompression of ulnar nerve at level of Guyon's canal compared with normal nerve. Transverse sonogram of affected side in 27-year-old man reveals that decompressed nerve is markedly swollen and surrounded by scar tissue (arrows). Internal architecture of nerve is disorganized; therefore, neuroma was suspected. On subsequent surgery, only swollen fascicles and tight scar formation, but no neuroma, were seen.

View larger version (101K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7B. —Decompression of ulnar nerve at level of Guyon's canal compared with normal nerve. Transverse sonogram of unaffected side in 27-year-old man (same patient as in A) shows normal nerve diameter and internal structure (arrow) and normal surrounding soft tissues.

View larger version (108K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 7C. —Decompression of ulnar nerve at level of Guyon's canal compared with normal nerve. Transverse sonogram of surgically proven neuroma (arrow) in 40-year-old man who underwent tbial correction osteotomy is shown for comparison.

In one patient, only mild axonal swelling of the femoral nerve was revealed on sonography, but no compression could be seen. With conservative treatment, subsequent electrodiagnostic studies showed good functional recovery in 6 months, and no surgical exploration was performed.

Mean examination time (one examiner) was 25-30 min for examination of the injured nerve compared with the normal side.

Discussion

Top Abstract Introduction Subjects and Methods Results Discussion References

 
According to the literature, iatrogenic and postoperative nerve lesions are common [1,2,3,4]. The decision to treat surgically or conservatively is usually based on clinical examination and electrodiagnosis. These methods may reliably indicate which nerve is affected and differentiate between axonal loss with subsequent Wallerian degeneration and minor nerve lesions without axonal damage. In higher degree nerve lesions, complete recovery of nerve function will certainly not occur without surgical intervention; thus, the decision for surgery is straightforward.

If findings of neurology and electrophysiologic testing imply a smaller nerve lesion, a trial of conservative treatment will generally be recommended. Mere axonal swelling of a nerve without further compromise by surrounding structures will lead to complete recovery with conservative treatment. In nerves compressed by scars, hematomas, or bony spurs, however, complete recovery is unlikely, and in some patients, ongoing scar formation or organization and calcification of hematomas may even worsen the clinical situation. Consequently in many of these patients, recovery of nerve function is not achieved, and delayed surgical exploration is necessary. There is general agreement that early surgery may lead to shorter recovery times and better overall restitution of nerve function [8]. Therefore in these patients, conservative treatment may not only be useless but may even be associated with an increased risk of delayed recovery, with unfavorable outcome. In contrast to electrodiagnostic tests and clinical examination, high-resolution sonography has been shown to provide valuable information about the condition of the injured nerve in our patients. Hematomas and nerve compression by exuberant callus formation or surgical implants, and especially scar formation, could easily be shown.

On the other hand, surgery is associated with a certain risk of further nerve damage due to the surgical procedure itself, especially when a nerve that may be tightly packed within surrounding tissue is decompressed. Precise information about the condition of the nerve to be explored and the surrounding tissues gained with the use of high-resolution sonography is of great importance for the surgeon.

In all patients, the injured nerve could be visualized, and the level of injury could be determined. A thorough understanding of soft-tissue planes and anatomic guidelines is a prerequisite for quick and reliable identification of peripheral nerves. Nevertheless, it was quite troublesome to identify the nerve directly at the site of operation in patients in whom the nerve was surrounded by scar tissue or hematoma, and in these patients, direct visualization was impaired. As a general rule, it proved more feasible to identify the nerve proximal to the affected region according to known anatomic landmarks and to follow its course to the periphery. With this technique, the nerve could be identified in all patients, even when impacted by surrounding tissue.

The interpretation of local findings depends on a radiologist's knowledge of the normal sonographic appearance of peripheral nerves and their internal fascicular structure. On longitudinal scans, the rather distinct echotexture of peripheral nerves, which is detailed elsewhere [14], is normally composed of multiple hypoechoic and parallel, but discontinuous, linear areas separated by hyperechoic bands. Transverse scans show rounded hypoechoic structures that correspond to the neural fascicles embedded in a hyperechoic background of neural interstitium. A comparison of the injured side and the nerve at the unaffected side is especially important for the diagnosis of minor injuries, such as diffuse axonal swelling, because the sonographic findings in these patients may be subtle. Minor postoperative lesions are often caused by temporary compression or traction of the nerve during surgery. Thus, their pathologic correlate is a localized disturbance of the intraneural microvascular supply and subsequent inflammatory reaction. Ensuing venous congestion and internal edema results in a loss of the fascicular nerve structure and a thickened uniformly hypoechoic appearance. The same is true for a nerve proximal to the level of compression by a scar, whereas at the level of the scar itself, the nerve is generally flattened and may even be indistinguishable from the scar tissue. The differentiation of axonal swelling adjacent to a scar and a neuroma may, therefore, sometimes be difficult if the continuity of the nerve cannot be shown at the site of the scar. This problem was shown in one of our patients in whom a suspected neuroma could not be confirmed at surgery. If continuous nerve fascicles can be shown, axonal swelling is more likely, but sometimes when the nerve is markedly thickened and edematous, this differentiation may be impossible. However, we do not think that this problem should be important for the therapeutic decision because a trial of conservative treatment will be appropriate for both conditions.

We conclude that high-resolution sonography can compensate for the limitations of electrodiagnosis in the assessment of postoperative peripheral nerve lesions and may be especially helpful in deciding if early surgical treatment is to be instituted. We do not recommend sonography as the only tool for identification and localization of lesions, but we believe that it may serve as an important adjunct in patients with these lesions by revealing important diagnostic information that is beyond the scope of other diagnostic modalities.

References

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