High-resolution ultrasound of the sural nerve

Transcription

1 High-resolution ultrasound of the sural nerve Poster No.: C-2084 Congress: ECR 2012 Type: Educational Exhibit Authors: D. Belsack, T. Jager, M. De Maeseneer, K. Vanderdood, S Marcelis ; Brussel/BE, Aalst/BE, Brussels/BE, Sittard/NL, 5 Tielt/BE Keywords: Neuroradiology peripheral nerve, Musculoskeletal soft tissue, Extremities, Ultrasound, Observer performance, Pathology DOI: /ecr2012/C-2084 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 15

2 Learning objectives 1. To demonstrate the normal sural nerve, as seen on ultrasound, correlated with anatomical dissection. 2. To present a pictorial overview of pathologic conditions that affect the sural nerve. Page 2 of 15

3 Background Advances in ultrasound technology have resulted in improved spatial and contrast resolution, allowing visualisation of small peripheral nerves. To the best of our knowledge, little has been published regarding ultrasound of the sural nerve. Sural nerve pathology is uncommon and patients usually present with nonspecific findings, most commonly lateral ankle pain or numbness. Page 3 of 15

4 Imaging findings OR Procedure details 1. The sural nerve is a sensory peripheral nerve supplying the cutaneous part of the dorsolateral aspect of the heel and the foot. The nerve is composed of branches derived from the spinal nerve roots S1 and S2. The lesser saphenous vein is an important landmark, the sural nerve runs along with the vein superficially to the gastrocnemius muscle at the posterior side of the lower leg. Its terminal branches consist of the lateral dorsal cutaneous nerve and the lateral calcaneal branches (Fig. 1). Essentially, the internal architecture of the sural nerve does not differ from that of other peripheral nerves. On US, the sural nerve presents as an ovoid slightly hypoechoic structure, in comparison with the surrounding fat tissue, with more hypoechoic dots (neuronal fascicles). The nerve is found in close proximity to the lesser saphenous vein (Fig. 2, Fig. 3). 2. Six cases of proven (by surgery, laboratory and/or electrophysiology) sural nerve disorders were included in this study. All examinations were performed by experienced musculoskeletal radiologists with the use of linear-array high frequency transducers (13 MHz). - Entrapment neuropathy is characterized by focal nerve enlargement and hypoechogenicity due to edema in the nerve as result of friction. Figure 4 shows a focal thickened hypoechoic sural nerve in a 36 year old male with osteomyelitis after surgery for a calcaneal fracture. Another case of entrapment neuropathy of the sural nerve is presented due to thrombus formation along its course after stripping surgery of the lesser saphenous vein (Fig. 5). - In posttraumatic or post-interventional nerve damage (Fig. 6) or transsection (Fig. 7), ultrasound was able to demonstrate focal nerve discontinuity. In a later phase, formation of a spindle neuroma (in nerve trauma with axonal damage without complete transsection) or a terminal neuroma (in nerve transsection) can be depicted. These neuromas are the result of Schwann cells trying to restore the continuity of the nerve, presenting as a hypoechoic fusiform thickening of the nerve proximal to the site of nerve damage. - Nerve inflammation is seen as diffuse hypoechoic nerve enlargement with loss of echostructure. An increased Doppler signal can be seen. We present a case of inflammatory sural nerve neuropathy in a 56 year old male with laboratory proven Lyme's disease (Fig. 8, Fig. 9). - Tumoral lesions deriving from peripheral nerves are divided in benign and malignant nerve sheath tumors (BPNST/MPNST). BPNST's present as a fusiform homogeneous and hypoechoic mass along the course of the nerve, sometimes with small calcifications or anechoic cysts within. Schwannoma tend to be larger, solitary and eccentric, while Page 4 of 15

5 neurofibroma are usually smaller, multifocal and along the nerves axis. MPNST's are more inhomogeneous and irregular with a variable size and a distinct hypervascularity. They are more frequently located in proximity of the nerve trunk. We present a case of fusiform tumoral enlargement of the sural nerve, due to a BPNST, most likely to be a Schwannoma (Fig. 10). Page 5 of 15

6 Images for this section: Fig. 1: Anatomical dissection of the sural nerve (paper markers), next to the lesser sapheneous vein at the porsterior side of the lower leg and running towards the dorsolateral side of heel and foot. Page 6 of 15

7 Fig. 2: Normal US appearance of the distal sural nerve at the level of the distal lower leg. Axial imaging plane. Fig. 3: Diagram of the normal US appearance of the distal sural nerve as seen in figure 2. Page 7 of 15

8 Fig. 4: US appearance of distal sural nerve entrapment neuropathy caused by edema in a patiënt with osteomyelitis, showing a hypoechoic thickening of the nerve (open arrow) due to friction, in the transverse plane. The arrow shows the doppler signal of the lesser saphenous vein. Notice the marked periosteal elevation and subperiosteal abcess formation at the level of the calcaneum (arrow heads). Page 8 of 15

9 Fig. 5: US appearence of entrapment neuropathy of the sural nerve in the transverse plane, with hypoechoic thickening of the nerve (arrow). The cause of the friction is thrombic material at the site of the lesser saphenous vein (open arrow) after stripping surgery. Page 9 of 15

10 Fig. 6: Formation of a spindle neuroma (dotted green line demarcation), seen as a focal hypoechoic thickening, of the sural nerve in a patient after nerve trauma due to stripping surgery of the lesser saphenous vein, without complete trassection of the nerve. Longitudinal image plane. Fig. 7: Longitudinal US image of a recent sural nerve transsection after penetrating trauma. There is a normal appearence of the proximal and distal part of the nerve (arrow). The open arrow shows an anechoic gap, proving the transsection of the nerve. The subcutaneous tissue is partly obscured by artefacts originating from the skin, caused by scar formation. A terminal neuroma has not yet been formed. Page 10 of 15

11 Fig. 8: US appearance of inflammatory neuropathy of the right sural nerve in a patiënt with proven Lyme disease, longitudinal plane. Normal appearance of the proximal nerve (arrow) and inflammatory thickening of the distal nerve (open arrow). Fig. 9: US appearance of inflammatory neuropathy of the sural nerve of the right leg (open arrow) in a patient with proven Lyme disease, transverse plane. Comparison with the normal left sural nerve (arrow). Page 11 of 15

12 Fig. 10: US of a hypoechoic neurogenic tumor, originating from the sural nerve with a normal appearance of the nerve distal to the tumor. Note the presence of hyperechoic microcalcifications. Eccentric location compared to the nerve, most likely Schwannoma. Page 12 of 15

13 Conclusion State-of-the-art high-resolution ultrasound equipment is able to depict a wide spectrum of disorders of the sural nerve. Ultrasound provides a readily available and inexpensive imaging modality with higher spatial resolution compared to MRI. As such, ultrasound should be considered the first choice imaging modality for assessment of suspected sural nerve disorders. Page 13 of 15

14 Personal Information Dr Belsack Dries Radiology Department UZ Brussel Laarbeeklaan Brussels Page 14 of 15

15 References Simonetti S, Bianchi S, Martinoli C (1999) Neurophysiological and ultrasound findings in sural nerve lesions following stripping of the small saphenous vein. Muscle Nerve 22: Fornage BD (1988) Peripheral nerves of the extremities: imaging with US. Radiology 167: Martinoli C, Bianchi S, Derchi LE (1999) Tendon and nerve sonography. Radiol Clin North Am 37: Martinoli C, Bianchi S, Derchi LE (2000) Ultrasonography of peripheral nerves.semin US CTMR 21: Beekman R, Visser LH (2004) High-resolution sonography of the peripheral nervous system: a review of the literature. Eur J Neurol 11: Silvestri E, Martinoli C, Derchi LE et al (1995) Echotexture of peripheral nerves: correlation between US and histologic findings and criteria to differentiate tendons. Radiology 197: Jacobson JA, Jebson PJL, Jeffers AW et al (2001) Ulnar nerve dislocation and snapping triceps syndrome: diagnosis with dynamic ultrasonography report of three cases. Radiology 220: Bianchi S, Martinoli C (2007) Ultrasound of the musculoskeletal system. Springer-Verlag, Berlin Heidelberg New York Graif M, Martinoli C, Rockind S et al (2004) Sonographic evaluation of brachial, plexus pathology. Eur Radiol 14: Provost N, Bonaldi VM, Sarazin L (1997) Amputation stump neuroma: ultrasound features. J Clin Ultrasound 25:85-89 Martinoli C, Derchi LE, Bertolotto M et al (2000)USand MR imaging of peripheral nerves in leprosy. Skeletal Radiol 29: Lin J, Martel W (2001) Cross-sectional imaging of peripheral nerve sheath tumors: characteristic signs on CT, MR imaging and sonography. Am J Roentgenol 176:75-82 Reynolds DL Jr, Jacobson JA, Inampudi P et al (2004) Sonographic characteristics of peripheral nerve sheath tumors. Am J Roentgenol 182: Peer S, Bodner G (2008) High-Resolution Sonography of the Peripheral Nervous System. Springer-Verlag, Berlin Heidelberg New York Gruber H, Glodny B, Bendix N et al (2007) High-resolution ultrasound of peripheral neurogenic tumors. Eur Radiol 17: Page 15 of 15