Assessment of the utility of ultrasonography with high-frequency transducers in the diagnosis of postoperative neuropathies

Abstract

The primary aim of this paper was to assess the relevance of high-frequency ultrasound examination in qualifying patients for either surgical or conservative treatment of postoperative peripheral neuropathies. The study was conducted in a group of 71 patients who in 2009–2011 were referred to ultrasound examinations due to a clinical suspicion of peripheral neuropathies. For the purposes of this analysis, the suspected postoperative neuropathies were divided into three groups: after surgical treatment of the median nerve (1), after surgical treatment of the ulnar nerve (2) and other postoperative neuropathies (3). All patients underwent the interview, physical examination and ultrasound examination. The ultrasound examinations were performed with Esaote MyLab 50 and MyLab 60 systems. Based on the clinical and US examinations, the patients were qualified for either surgical (51 cases) or conservative treatment (20 cases). An EMG examination was also performed in certain patients (60 cases). Mean values of cross-sectional areas and diameters of the nerve trunks were calculated in individual pathology groups. The ultrasound features of the peripheral nerves analyzed in the study, such as echostructure, notch sign, hyperemia and continuity of the transverse ligament, were divided into subgroups. Moreover, the frequency of adhesions between the nerve trunks and adjacent tissues, occurrence of pain on compression with a transducer and instability of the ulnar nerve as well as angulation of the posterior interosseous nerve in a dynamic examination was calculated. The analyses of the collected material were performed by means of descriptive statistics. The results of clinical and surgical verification were consistent with ultrasound findings in 100% of cases. The results indicate that high-frequency ultrasonography is a valuable method in qualifying patients for various types of treatment of peripheral postoperative neuropathies.

Introduction

Ultrasound nerve evaluation after surgical procedures requires extensive experience and knowledge of surgical techniques⁽¹⁾. The image of the nerve is frequently permanently altered, which results from the healing physiology of soft tissues with scar formation.

Following decompression procedures of entrapment neuropathies, US assessment involves not only the structure of the nerve, but also the radicality of the procedure. One should pay attention to even slight remaining fibrous bands which may cause persistent compression of the nerve, e.g. incompletely cut transverse ligament of the carpal tunnel in CTS⁽²⁾.

In the cases of ulnar nerve compression, the aim of the procedure is to remove the cause of neuropathy, i.e. to cut the arcuate ligament, to cut the fibers of the medial intermuscular septum of the arm or to remove a pathological mass (accessory anconeus muscle, lipoma, angioma). In the past, it was common to translocate the nerve trunk to the anterior surface of the epicondyle of the humerus following decompression. Currently, this technique is being departed from and replaced with so-called simple release.

A similar surgical procedure involves the PIN and AIN and consists in cutting or removing fascial thickening and fibrous bands, removing pathological tissue masses or ligating the vascular bundles crossing the nerve trunk.

The main aim of ultrasound postoperative assessment of posttraumatic changes is to answer the question whether the nerve continuity has been restored and whether a neuroma or adhesions between the adjacent tissues formed at the site of suturing.

Other reasons for postoperative complications are iatrogenic disruption of the nerve trunk continuity (direct action of a scalpel), nerve entrapment under a bone plate and irritation by a protruding screw thread.

A surgical procedure for a peripheral nerve tumor depends on its type. In the case of schwannoma, a surgery consists in the separation of the tumor from adjacent nerve bundles in the least traumatic way possible. This is performed after opening the epineurium.

In the case of neurofibroma, the procedure is much more mutilating and associated with the removal of a fragment of the nerve trunk together with the tumor.

As for lipomas or fibromas of the nerve sheaths, they are removed without compromising the nerve structure (as in schwannoma).

In order to rule out adhesions between the nerve trunk and adjacent tissues, dynamic assessment is a permanent element of postoperative examinations.

Material and methods

The primary aim of this paper was to assess the relevance of high-frequency US examination in qualifying patients for either surgical or conservative treatment of postoperative peripheral neuropathies.

The specific objectives were:

• to specify ultrasound features of peripheral neuropathies in terms of their qualification for surgical or conservative treatment;

• to determine the diagnostic value of ultrasonography in the assessment of peripheral postoperative neuropathies with respect to clinical and surgical verification as well as results of functional examinations.

The material for the study consisted of 71 patients aged 22–82 (mean age 55.5) who in 2009–2011 were referred to ultrasound examinations due to a clinical suspicion of peripheral postoperative neuropathies.

For the purposes of the analysis, the patients were divided into three groups:

1. patients after surgical treatment involving the median nerve (50 cases);

2. patients after surgical treatment involving the ulnar nerve (11 cases);

3. patients with other peripheral postoperative neuropathies (10 cases).

The group included 21 males aged 22–80 (mean age 47) and 50 females aged 24–82 (mean age 59) (Fig. 1).

Fig. 1.

Mean age in individual categories of postoperative neuropathies

The patients were referred to a US examination by orthopedists, neurologists and physiotherapists. All patients gave written consent to the participation in the study. The examinations were conducted in two health care facilities in Krakow: Intermed and TLK Med.

The US examinations were performed with Esaote MyLab 50 and MyLab 60 systems using high-frequency broadband linear transducers: 6–18 MHz (mainly of 12–18 MHz).

The nerves were evaluated in the gray-scale and in the power Doppler mode in longitudinal and transverse planes in terms of:

• localization, morphology and the grade of neuropathy;

• possible anatomic variants of the nerve trunk and pathologies of the adjacent tissues.

Furthermore:

• a dynamic examination was performed to observe the sliding of the nerve trunk in relation to the adjacent tissues in the maximal movement range of the nearest joints;

• the motor and sensory-motor nerves were assessed indirectly based on images of the skeletal muscles innervated by these nerves.

The US images were analyzed with clinical signs (all patients) and EMG results (60 patients) in mind.

The analyses of the collected material were performed by means of descriptive statistics. Mean values of cross-sectional areas and diameters for individual pathology groups were calculated. The ultrasound features of the peripheral nerves evaluated in the study, such as echostructure, notch sign, hyperemia and the continuity of the transverse ligament, were divided into subgroups to determine the most common features of a US image of the nerves analyzed in the individual neuropathy groups. Moreover, the frequency of adhesions between the nerve trunks and adjacent tissues, occurrence of pain upon compression with a transducer, instability of the ulnar nerve as well as angulation of the nerve trunk in a dynamic examination was calculated. The agreement of the US examinations with EMG tests, clinical examination and surgical verification was also checked. The values obtained were presented in the figures.

The article is the third part of a series of publications prepared on the basis of the author's doctoral dissertation entitled: Usefulness of ultrasonography with high-frequency transducers in the diagnosis of peripheral neuropathies (supervised by: Prof. Iwona Sudoł-Szopińska, defended on November 4, 2014 in Warsaw).

Results

In the patients with symptoms of peripheral neuropathies, 71 pathologies were diagnosed in a US examination.

The following ultrasound features were analyzed:

• nerve trunk continuity;

• echostructure of the peripheral nerves;

• vascularization of the peripheral nerves;

• measurement results;

• notch sign in the nerve;

• continuity of the transverse ligament in the carpal tunnel.

The examination involved longitudinal footprint application at the level of the carpal tunnel. The retained continuity of even single bands of the transverse ligament was considered a pathological sign (Fig. 2 A, B).

• stability of the ulnar nerve at the level of the humeral groove;

• adhesions.

Fig. 2.

Incomplete cutting of the transverse ligament: A. US image – area of compression (arrow), nerve (arrow heads); B. intraoperative image

The aforementioned terms were explained in the articles entitled: Assessment of the utility of ultrasonography with high-frequency transducers in the diagnosis of entrapment neuropathies⁽⁴⁾ and in Assessment of the utility of ultrasonography with high-frequency transducers in the diagnosis of posttraumatic neuropathies⁽⁵⁾.

Based on the clinical and US examinations, the patients were qualified for either surgical or conservative treatment. Fifty-one patients were operated, and 20 received conservative treatment.

The analysis of the usefulness of ultrasonography in qualifying patients for either surgical or conservative treatment of peripheral neuropathies was based on the comparison of the elements of US nerve assessment with the result of the clinical examination, EMG test and intraoperative verification.

Postoperative nerve assessment requires knowledge of the pathologies operated and surgical techniques applied.

After decompression procedures in entrapment syndromes, the US examination involved the assessment of echostructure, epineurium continuity, bundle structure continuity, degree of peripheral nerve vascularization, radicality of the procedure and presence of adhesions between the adjacent tissues.

In the case of entrapment syndromes which had persisted for many years, the return of the correct bundle echostructure following the release procedure was not always observed despite clinical improvement (Fig. 3).

Fig. 3.

Persistent degenerative changes in the median nerve despite correct surgical procedure

In certain cases, hyperemia and edema of the nerve persisted for many weeks. In an early postoperative period, any fluid collection in the direct surroundings of the nerve and inflammatory granulation were considered a pathology.

A persisting effect of an hourglass-like narrowing of the nerve (viewed with the transducer applied longitudinally) was always considered an unfavorable phenomenon and attested to the lack of the radicality of the procedure. This resulted from leaving a part of fibers or one of the fibrous structures that had caused preoperative compression (transverse ligament of the carpal tunnel, Osborne's ligament, Struthers’ ligament, fascial band compressing the PIN etc.).

In a late postoperative period, a frequent reason of recurring symptoms were adhesions that reduced or even prevented nerve sliding against adjacent tissues.

In postoperative assessment of ulnar nerve entrapment, the technique of nerve transposition to the anterior surface of the condyle of the humerus was included (Fig. 4). During a US examination, the nerve was clearly visible on the border of the subcutaneous tissue and fascia, on the anterior outline of the epicondyle. Particular attention was then paid to the potential bending site of the proximal fragment of the transposed nerve at the level of the arcuate ligament in relation to the fragment located between the heads of the flexor carpi ulnaris muscle. A large degree of bending caused secondary neuropathic syndromes.

Fig. 4.

A, B, C. Ulnar nerve transposition and D. an ultrasound image – nerve (arrow) on the anterior outline of the epicondyle (asterisk)

Following surgical repair of posttraumatic changes – complete injury – the most important parameter was the restoration of the nerve trunk continuity. When the end-to-end technique had been used to suture the nerve, a one-level scar was visible (Fig. 5). When, however, a graft or neurotube had been used, scars were present at two levels (Fig. 6).

Fig. 5.

Normal image of the healed suturing site of a peripheral nerve (sutures are marked with arrows): A. longitudinal plane; B. transverse plane

Fig. 6.

A. Intraoperative image of a neurotube; B. ultrasound image (arrows)

A slight spindle-like thickening of the nerve trunk outlines at the site of the sutures was a normal postoperative presentation. When high-frequency transducers were used, slight, hyperechoic points were clearly visible at the level of suturing. They corresponded to microsurgical sutures. A neuroma at the site of suturing caused considerable dilatation of the nerve trunk outlines, sometimes irregular, and disordered echostructure (Fig. 7).

Fig. 7.

Neuroma at the suturing site of a peripheral nerve

Not always did it involve the entire section of the nerve; sometimes it affected only single bundles. It showed enhanced vascularization in the Doppler mode.

A permanent and significant element of postoperative assessment was a dynamic examination during which a slide of the nerve in relation to the adjacent tissues was observed in a longitudinal plane. So called “tightening” of the tissues or, in extreme cases, “wrinkling” of the nerve attested to the presence of adhesions.

Following surgical treatment of peripheral nerve tumors and tumor-like lesions, a US examination mainly involved the radicality of lesion removal and possible iatrogenic injury. The following were analyzed: continuity of the epineurium and perineurium, vascularization of the nerve at the site which was operated and nerve sliding in relation to the adjacent tissues as evidence of the absence of adhesions.

Comparison of EMG and US findings

An EMG examination was conducted in 60 patients (90% in group 1, 80% in group 2 and 63.6% in group 3). In 55 patients, the result was consistent with ultrasound findings and intraoperative assessment. In 5 patients, the EMG result was not confirmed either in ultrasonography or intraoperatively.

Discussion

The group of analyzed peripheral nerve changes consisted of 71 cases of postoperative complications. Complications after surgical treatment of CTS were the most frequent (50 patients). The remaining complications followed surgeries involving the ulnar nerve (11) and other peripheral nerves (10).

Postoperative median nerve pathologies (50 patients)

The most common causes due to which the symptoms recurred or failed to subside following primary surgical treatment of CTS were incompletely cut flexor retinaculum (37 cases – 74%) or adhesions between the adjacent tissues (29 cases – 58%). Blurred nerve echostructure or its absence were the dominant features of the US image (28 and 19 cases, respectively). Hyperemia was observed in 27 patients (54%), and notch sign – in 22 patients (44%). EMG was conducted in 45 patients (90%) and confirmed the clinical diagnosis in 43 cases (95.56% of patients examined with this method) (Tab. 1). Thirty-eight of 50 patients (76%) were operated; the remaining patients received conservative treatment. The necessity of a repeated surgery was determined by an ultrasound examination based on the transverse ligament image or a result of a dynamic examination involving nerve entrapment in adhesions.

Tab. 1.

Frequency in which individual ultrasound elements occurred in patients with symptoms of CTS remission

The problem of incomplete sectioning of the transverse ligament was also noticed by Turkish authors⁽²⁾. They conducted an experiment that involved using ultrasonography to check the completeness of transverse ligament sectioning intraoperatively during procedures with socalled limited incisions in 32 women. The intraoperative assessment confirmed the radicality of the procedure in all patients.

Postoperative ulnar nerve pathologies (10 patients)

Based on a US examination, 7 of 10 patents with clinically suspected recurrence of neuropathy were qualified to a repeated surgery involving the ulnar nerve. Three patients received conservative treatment and were monitored. Disordered echostructure and hyperemia were observed in 80% of cases. An EMG examination was performed in 8 patients – the clinical and ultrasound diagnosis was confirmed in 60% of patients. Adhesions were found in 60% of patients (Tab. 2). In 5 cases, simple nerve release was performed, and in 2 – ulnar nerve transposition was conducted.

Tab. 2.

Frequency in which individual ultrasound elements occurred in patients with symptoms of CubTS remission

A particular case was that of a 32-year-old male patient who sustained multiple internal injuries. Apart from lifesaving procedures, ulnar nerve “Z-plasty” was conducted which consists in the multiple bending of the nerve trunk that had lengthened due to stretch injury. Based on a US examination, which confirmed the type of the procedure, the patient was qualified to a repeated surgery – removing a fragment of the damaged nerve and “end-to-end” suturing of normal nervous tissue.

Postoperative pathologies of other nerves (11 patients)

The following peripheral neuropathies were assessed in this group: median, ulnar, radial, peroneal, of slight cutaneous nerves in the region of postoperative scars and of the posterior interosseous nerve.

A postoperative US examination is conducted in patients with persisting symptoms or with their recurrence. The examination requires knowledge of not only the US presentation of the nerve, but also surgical techniques, which are carefully discussed in one of American books⁽¹⁾. Moreover the publication on postoperative complication imaging in 18 patients (verified intraoperatively in 8 cases and with diagnostic biopsy in 10 cases) published in 2001 is also of educational value⁽⁶⁾. The most common causative factors of iatrogenic injuries were, according to the authors: nerve transection, its traction, and electrocoagulation heat. In the author's own paper, conflict with the suturing material (5 patients) and traction (3 patients) were the prevailing causes. Moreover, attention was also paid to iatrogenic injuries independent of the surgeon – resulting from the presence of a hematoma or a scar that forms later. The authors emphasized that a US examination is frequently a decisive tool in qualifying patients to revision procedures, particularly because the remaining diagnostic tools, mainly EMG, are not reliable. These conclusions are in line with the author's own observations; in the group of patients who underwent an EMG examination, the result was surgically confirmed in 93% of cases whereas a US image was confirmed in all the patients. Postoperative scars that encased the nerves were observed in merely 7 patients (39%) in the aforementioned publication. In this study, there were more such complications: adhesions between the nerve and the surrounding tissues were observed in as many as 58% of cases following carpal tunnel release, 60% of patients following ulnar nerve surgery, and 72.7% of patients who underwent other procedures (Tab. 3). The difference may result from the technique of a dynamic examination and the profile of the procedures (conducted by surgeons that cooperated with the author) which usually were entrapped nerve release and treatment of postoperative and posttraumatic complications rather than emergency procedures. The Austrian authors claimed that the main criterion of postoperative pathology was nerve outline thickening. It is, however, questioned by other authors⁽⁷⁾ as non-specific and occurring in various neuropathies, which is consistent with the author's own observations.

Tab. 3.

Frequency in which individual ultrasound elements occurred in patients with remission symptoms of peripheral neuropathies other than CTS or CubTS

In 2003, Peer et al. presented an analysis of 19 patients after primary repair of peripheral nerve injuries (10 median nerves, 10 ulnar nerves, 5 digital nerves and 1 radial nerve)⁽⁸⁾. The authors assessed the following during ultrasonography: the level of repair, continuity of the epineurium, continuity of the perineurium, nerve echostructure, its relation to the adjacent tissues (adhesions), size of nerve scar (neuroma) and the presence of sutures. In 22 patients, they visualized neuromas, in 4 – scars of the nerve and surrounding tissues, and in 11 – disordered echostructure or discontinuity of the nerve at the site of suturing. The authors’ techniques of the examination and conclusions are consistent with those applied and obtained by the author of this study.

The most common iatrogenic injuries of peripheral nerves involve the radial nerve. In the author's own study, there was a case of a 22-year-old man after multiple organ trauma with humeral bone fracture fixed with intramedullary nailing. A US examination revealed a complete, unrepaired injury of the radial nerve with both stumps encased between the fragments of the fractured bone. The second patient was a 27-year-old man with fractured humerus fixed with a plate, in whom the radial nerve was entrapped under the plate. A team of French authors presented 30 similar cases of iatrogenic radial nerve injuries⁽⁹⁾.

A particularly interesting case in the author's own material was median nerve irritation by a long protruding screw after humerus fixation. There are no reports of such cases in the literature. The US image was confirmed intraoperatively.

In another patient, transient PIN palsy developed after radial bone fixation with the use of a bone plate. Thanks to ultrasonography, which visualized the nerve with unimpaired continuity in the direct vicinity of the plate with no signs of entrapment, revision surgery was not conducted. The nerve returned to its full function, and the injury mechanism was probably neuropraxia. Other reports present similar cases^{(8, 9)}. The same mechanism caused transient palsy of the right common peroneal nerve in a 55-year-old female patient after knee joint replacement. The EMG examination revealed severe injury to this nerve. The patient underwent four ultrasound examinations. Consecutive US scans showed a gradual reduction of nerve trunk edema, which was observed as decreasing cross-sectional diameter, return of the bundle presentation and reduced hyperemia. After 6 months, a complete return of superficial and deep sensation as well as a partial return of muscle strength were observed. The author has not found any reports concerning ultrasound presentation of similar complications. The attention is drawn to the role of EMG and, of course, to the clinical examination. Thanks to using high-frequency transducers, a US examination helps determine the grade of structural nerve damage (extent, percent of damaged fascicles) and the presence of e.g. a hematoma that needs evacuation.

Conclusions

High-frequency ultrasonography is a valuable modality in qualifying patients to surgical procedures or conservative treatment of postoperative peripheral neuropathies.

1. The ultrasound features of peripheral nerve injuries which in the author's own studies occurred to be the most relevant in terms of qualifying patients for surgical or conservative neuropathy treatment were:

   • diameter or cross-sectional area of the nerve at the site of the visualized pathology;
   • nerve echostructure, hyperemia;
   • presence of adhesions or instability in a dynamic US examination;
   • abnormalities of the adjacent tissues (including muscles, bone surfaces and tendon sheaths);
   • pain reaction to nerve compression with the transducer.

2. The results of the clinical and surgical verification were consistent with the ultrasound findings in all cases.

Conflict of interest

The author does not report any financial or personal links with other persons or organizations, which might negatively affect the content of this publication and claim authorship rights to this publication