In the past, diagnosis of peripheral neuropathy

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1 Sonography of the Normal Ulnar Nerve at Guyon s Canal and of the Coon Peroneal Nerve Dorsal to the Fibular Head Els Y. Peeters, MD, Koenraad H. Nieboer, MD, Michel M. Osteaux, MD, PhD Department of Radiology, University Hospital Vrije Universiteit Brussel, Laarbeeklaan 101, B-1090 Brussels, Belgium Received 3 April 2003; accepted 24 February 2004 ABSTRACT: Purpose. This study was conducted to evaluate the ability of sonography to visualize the ulnar nerve at Guyon s canal and the coon peroneal nerve dorsal to the fibular head and to test for correlations between nerve measurements and subject characteristics. Methods. We used a 5 12-MHz linear-array transducer in sonographic evaluation of 15 healthy adult volunteers. We evaluated the correlations between nerve diameters and surface areas and subject body mass index and height. We also tested for differences between nerve measurements in women and men and between nerve measurements from the left and right sides of the body. Results. Both nerves were visualized in all subjects. Subject height correlated significantly with the anteroposterior diameter of the right ulnar nerve. Body mass index correlated significantly with the surface area of both ulnar nerves, with the anteroposterior diameter of both ulnar nerves, with the transverse diameter of the left ulnar nerve, and with the transverse diameter of the right coon peroneal nerve. There was a statistically significant difference in anteroposterior diameter of the left ulnar and left coon peroneal nerves between women and men. There were no significant differences between left- and right-side measurements for the combined data from the entire group of subjects. Conclusions. A 5 12-MHz linear-array transducer readily allows for visualization of the ulnar nerve at Guyon s canal and the coon peroneal nerve dorsal to the fibular head. ª 2004 Wiley Periodicals, Inc. J Clin Ultrasound 32: , 2004; Published online in Wiley InterScience ( DOI: /jcu Correspondence to: E. Y. Peeters Ó 2004 Wiley Periodicals, Inc. Keywords: ultrasonography; ulnar nerve; coon peroneal nerve; entrapment neuropathy In the past, diagnosis of peripheral neuropathy was based on the patient s history, findings on physical examination, and results from electrophysiologic tests. Electrophysiologic tests do not provide morphologic information about a nerve and surrounding tissues, which could help determine the etiology of the neuropathy. 1 Furthermore, nerve conduction measurements reflect the status of only the best surviving fibers and consequently can yield normal results if even only a few fibers remain unaffected by a disease process. 2 Improved sonographic technology including high-frequency broadband transducers, compound imaging, high near-field resolution, and extended field-of-view techniques makes noninvasive evaluation of peripheral nerves and neuropathies possible. MRI is another appropriate method for noninvasive diagnosis of nerve disorders, but it is more expensive, more time consuming, and less widely accessible than sonography. Until now, most sonographic investigations of nerves have been focused on the median nerve in carpal tunnel syndrome and on the ulnar nerve in cubital tunnel syndrome. However, the systematic sonographic identification of the normal ulnar nerve at Guyon s canal has not been investigated. In addition, only Heinemeyer and Reimers 3 have systematically evaluated the ability of sonography to visualize the coon peroneal nerve dorsal to the fibular head. Using a 7.5-MHz linear-array transducer, they could not depict the coon peroneal nerve in any of 50 healthy subjects. 3 VOL. 32, NO. 8, OCTOBER

2 In the present study, we investigated the ability of sonography to detect the ulnar nerve at Guyon s canal and the coon peroneal nerve dorsal to the fibular head in 15 healthy adult volunteers. We also measured the diameters and surfaces of these nerves cross sections at these sites and investigated possible correlations between these measurements and patients heights and body mass indices (BMIs). Furthermore, we investigated whether there are significant differences in measurements between women and men and between the left-hand nerves and right-hand nerves. PEETERS ET AL SUBJECTS AND METHODS The study group comprised 15 randomly selected healthy adult volunteers (7 women and 8 men), drawn from the population of medical students and residents in the Department of Radiology at our institution. Neuromuscular disease, peripheral nerve lesions, diabetes mellitus, alcoholism, and other possible causes of neuropathy excluded subjects from the study. Subjects gave their oral informed consent to participate. The subjects ages ranged from 21 to 32 years (mean, 25.1 years), they had a mean body weight of 66.9 kg (range, kg), a mean height of 1.72 m (range, m), and a mean BMI of 22.4 (range, ). All subjects were right-handed. An HDI 5000 ultrasound scanner (Philips-ATL, Bothell, WA) equipped with a 5 12-MHz lineararray transducer was used. Compound imaging and high-definition zoom features were used. Care was taken not to apply excessive compression to the tissues examined before measuring the nerve diameters and cross-sectional areas. Sonographic examination of the ulnar nerve was performed with the dorsal side of the forearm resting on the examination table (Figure 1A); the patient lay in the prone position on the examination table for examination of the coon peroneal nerve (Figure 1B). On sonograms, nerves appear as multiple hypoechoic parallel linear areas separated by hyperechoic bands on longitudinal scans and as hypoechoic, rounded areas embedded in a hyperechoic background on transverse scans. 2,4,5 The hypoechoic structures correspond to fascicles of axons, and the hyperechoic background corresponds to the interfascicular endoneurium. We could easily visualize the ulnar nerve lying between the pisiform and the ulnar artery. Systematic scanning on transverse planes allowed us to follow the coon peroneal nerve continuously from its origin from the sciatic nerve at the apex of the popliteal fossa until it emerged dorsal to the fibular head. FIGURE 1. Positioning of the transducer. (A) The examination of the ulnar nerve was performed with the dorsal side of the forearm resting on the examination table. The black line shows the position of the transducer at the level of the pisiform. (B) The examination of the coon peroneal nerve was performed with the patient lying in the prone position on the examination table. The black line shows the position of the transducer at the level of the fibular head. An outline of the fibula was drawn on the skin. All nerves were scanned bilaterally, in both transverse and longitudinal sections. The anteroposterior (AP) and transverse (TR) diameters of the nerves were measured on the transverse images (Figures 2A and 3A), as was the crosssectional area. The cross-sectional area was calculated automatically using the continuous trace method (Figures 2B and 3B). We calculated the arithmetic mean and 95% confidence interval for all the measurements. The Pearson s test was used to evaluate possible correlations between the various nerve measurements and the subjects BMI and height. A p value less than 0.05 in 2-tailed tests was considered significant. The nonparametric Wilcoxon s signed-rank test was used to evaluate differences between nerve measurements in women and men and between nerve measurements from the left and right sides. Again, p less than 0.05 was considered 376 JOURNAL OF CLINICAL ULTRASOUND

3 ULNAR AND COMMON PERONEAL NERVES FIGURE 2. Transverse sonograms of the right ulnar nerve in Guyon s canal. (A) Sonogram obtained using compound imaging shows the measurements of the anteroposterior (+ +) and transverse ( ) diameters of the nerve. The pisiform (arrow) and ulnar artery (arrowhead) are also seen. (B) Sonogram obtained using compound imaging shows the continuous trace used to calculate the crosssectional area (dotted ellipse). The pisiform (arrow) and ulnar artery (arrowhead) are also seen. (C) Sonogram obtained using compound scanning (right) shows the margins of the nerve (arrowhead) slightly better than the sonogram obtained without it (left). significant. All statistical analyses were performed using the Statistical Package for Social Sciences for Windows (SPSS, Chicago, IL). FIGURE 3. Transverse sonograms of the right coon peroneal nerve posterior to the fibular head. (A) Sonogram obtained using compound imaging shows the measurements of the anteroposterior (+ +) and transverse ( ) diameters of the nerve. The fibular head (arrow) is also seen. The lateral head of the gastrocnemius muscle (asterisk) is at the medial side. (B) Sonogram obtained using compound imaging shows the continuous tracing used to calculate the cross-sectional area (dotted ellipse). The fibular head (arrow) is also seen, as is the lateral head of the gastrocnemius muscle (asterisk). (C) Sonogram obtained using compound scanning (right) shows the margins of the nerve (arrowhead) slightly better than the sonogram obtained without it (left). RESULTS The ulnar nerve at Guyon s canal and the coon peroneal nerve dorsal to the fibular head could easily be visualized in all 15 subjects. The nerves were visualized more easily using compound imaging (Figure 2C and 3C) than using other techniques. The ulnar nerve presented with a circular, oval, or elliptic shape. The coon peroneal nerve appeared more flattened. Table 1 shows the mean values and 95% confidence intervals for measurements of the surface area, AP diameter, and TR diameter of the right and left ulnar and coon peroneal nerves for the entire subject group. Subject height correlated VOL. 32, NO. 8, OCTOBER

4 PEETERS ET AL TABLE 1 Mean Values and 95% Confidence Intervals (in Parentheses) for Nerves in the Entire Study Group TABLE 3 Mean Values and 95% Confidence Intervals (in Parentheses) for Nerves in Men Nerve Surface Area, 2 AP Diameter, TR Diameter, Nerve Surface Area, 2 AP Diameter, TR Diameter, Right ulnar 8.3* ( ) 2.5* ( ) 3.8 ( ) Left ulnar 8.5* ( ) 2.6* ( ) 3.7* ( ) Right coon peroneal 16.1 ( ) 3.1 ( ) 7.3* ( ) Left coon peroneal 15.7 ( ) 2.9 ( ) 6.9 ( ) Abbreviations: AP, anteroposterior; TR, transverse. *Correlation with body mass index is significant at the p < 0.05 level (2-tailed test). Correlation with height is significant at the p < 0.05 level (2-tailed test). significantly with the AP diameter of the right ulnar nerve (r ¼ 0.566; p < 0.05). BMI correlated significantly with the surface area of the right ulnar nerve (r ¼ 0.618; p < 0.05), the surface area of the left ulnar nerve (r ¼ 0.627; p < 0.05), the AP diameter of the right ulnar nerve (r ¼ 0.572; p < 0.05), the AP diameter of the left ulnar nerve (r ¼ 0.564; p < 0.05), the TR diameter of the left ulnar nerve (r ¼ 0.573; p < 0.05), and the TR diameter of the right coon peroneal nerve (r ¼ 0.533; p < There were no significant differences in measurements between the right and left ulnar and coon peroneal nerves for the entire subject group. The mean values and 95% confidence intervals for measurements of the surface area, AP diameter, and TR diameter of the nerves are listed separately for women and men in Tables 2 and 3, respectively. Women and men had a statistically significant difference in the AP diameter of the left ulnar nerve (p < 0.05) and in the AP diameter of the left coon peroneal nerve (p < 0.05). DISCUSSION Direct sonographic visualization of nerves can reveal a focal abnormality, differentiate neural TABLE 2 Mean Values and 95% Confidence Intervals (in Parentheses) for Nerves in Women Nerve Surface Area, 2 AP Diameter, TR Diameter, Right ulnar 7.0 ( ) 2.4 ( ) 3.4 ( ) Left ulnar 7.0 ( ) 2.3 ( )* 3.4 ( ) Right coon peroneal 15.9 ( ) 3.2 ( ) 6.7 ( ) Left coon peroneal 14.0 ( ) 2.6 ( )* 6.7 ( ) Abbreviations: AP, anteroposterior; TR, transverse. *P < 0.05 (significant difference between women and men). Right ulnar 9.4 ( ) 2.6 ( ) 4.2 ( ) Left ulnar 9.7 ( ) 2.9 ( ) 3.9 ( ) Right coon peroneal 16.4 ( ) 3.0 ( ) 7.7 ( ) Left coon peroneal 17.1 ( ) 3.2 ( ) 7.1 ( ) Abbreviations: AP, anteroposterior; TR, transverse. from extraneural tumors, and show the extent of a lesion and its relationship with vascular structures. In addition to compression of the median nerve in carpal tunnel syndrome and the ulnar nerve in cubital tunnel syndrome, entrapment neuropathies that are suited for sonographic examination are compression of the ulnar nerve in Guyon s tunnel, compression of the coon peroneal nerve at the fibular head, compression of the tibial nerve at the tarsal tunnel, and compression of the interdigital nerves in the intermetatarsal spaces. 6 Currently, sonography is not routinely used for the clinical assessment of these nerve pathologies because many radiologists and clinicians are still unaware of its potential for this application. Current ultrasound equipment efficiently identifies the median, digital, ulnar, and radial nerves in the upper limbs and the sciatic, coon peroneal, superficial peroneal, posterior tibial, medial and lateral plantar, calcaneal, and even interdigital nerves in the lower limbs Knowledge of nerve location and anatomic relations between the nerve and the surrounding structures is essential for sonographic identification. Examination of the nerves along transverse planes is preferable to longitudinal scanning because it allows following the nerves continuously throughout the limb. Because of the wide range of causes of neuropathies of the ulnar nerve at Guyon s canal and of the coon peroneal nerve dorsal to the fibular head, sonographic visualization of these nerves at these locations is of diagnostic importance. Although a true osteofibrous tunnel does not exist at the level of the fibular head, entrapment of the coon peroneal nerve typically occurs in the tight space between the fibular head and the fascia as the nerve winds around the back of the fibular neck, just under the skin. 16 Any change in the normal alignment of the nerve with the bone (eg, by misalignment after fibular fracture) may therefore result in entrapment syndrome. The differential diagnosis for peroneal neuropathy includes mononeuritis, idiopathic peroneal palsy, 378 JOURNAL OF CLINICAL ULTRASOUND

5 intrinsic and extrinsic nerve tumors, and extraneural compression by a synovial cyst, ganglion cyst, soft tissue tumor, bone tumor, or large fabella. 17 Traumatic injury of the nerve may occur secondary to a fracture or dislocation, surgery, application of skeletal traction, or a tight cast or bandage. 17 Even prolonged sitting with crossed legs and pressure during sleep have been reported to cause peroneal nerve compression. 18 Direct compression of a nerve may also be caused by posttraumatic hematoma or callus formation, as well as postoperative scars. Nerve sheath ganglia most frequently involve the large nerves around the knee, especially the peroneal nerve at the level of fibular head. Grossly, at the apex of the popliteal fossa, the sciatic nerve divides into 2 branches, the larger tibial and the smaller coon peroneal nerve. The coon peroneal nerve descends from the apex of the popliteal fossa obliquely through the popliteal fossa, winding around the lateral and anterior aspect of the fibular head and neck and passing laterally to the anterior compartment musculature and deeply to the 2 heads of the peroneus longus musculature to divide into deep and superficial branches. At the level of the popliteal fossa, the coon peroneal and tibial nerves have different sonographic appearances. The tibial nerve shows the typical echo pattern, with multiple hypoechoic parallel linear areas separated by hyperechoic bands appearing on longitudinal scans and hypoechoic, rounded areas embedded in a hyperechoic background appearing on transverse scans. The coon peroneal nerve has fewer and thicker fascicles, with less echogenic internal component. The difference in appearance is most likely related to the difference in the number of fascicles within those 2 nerves. 5 In 1999, Heinemeyer and Reimers 3 could not detect the peroneal nerve behind the fibular head using a 7.5-MHz linear-array transducer. 3 Until now, visualization of the nerve at this site has been described in only 1 patient by Fornage. 4 TheulnarnerveatGuyon scanallieslateraltothe pisiform and at the medial and dorsal aspect of the ulnar artery. Coon causes of ulnar neuropathy at Guyon s canal are ganglion cysts involving or affecting the pisotriquetrum joint, 15,19 22 occupational neuritis, laceration, ulnar artery disease (eg, pseudoaneurysms, arteritis), fractures (eg, of the hook of the hamate bone), retractile scar tissue, anomalous muscles (eg, accessory abductor digiti minimimuscle, anomalous hypothenar adductor), lipomas, giant cell tumors, 27 neurofibromas, and intraneural cysts. Chronic repeated external pressure by tools, canehandles, or crutches is the usual cause of ulnar nerve entrapment at Guyon s canal. 1 ULNAR AND COMMON PERONEAL NERVES Some more generalized diseases can affect both the ulnar nerve and coon peroneal nerve, as well as other nerves. Hereditary neuropathy with liability to pressure palsies, an autosomal dominant inherited disorder characterized by a tendency to develop focal painless neuropathies after trivial trauma, affects the peroneal nerve at the fibular head, the ulnar nerve at the elbow and at Guyon s canal, the radial nerve at the spiral groove, and the median nerve at the carpal tunnel. 28 Sonography may demonstrate nerve enlargement and hypoechogenicity. Furthermore, nerve hypertrophy is seen in the Charcot-Marie-Tooth syndrome (hereditary motor and sensory neuropathy types I and II), 3 and in Hansen s disease, a chronic infectious disease caused by Mycobacterium leprae, which in its various clinical forms primarily involves the skin and nerves. 29,30 By measuring the nerve crosssectional area sonographically, it was found that increased nerve size correlates with the presence of acute reactive states. 30 The present study was conducted to determine whether the ulnar nerve at Guyon s canal and the coon peroneal nerve dorsal to the fibular head can be detected using a 5 12-MHz transducer of the type coonly used for soft tissue examination. Our results indicate that these nerves can easily be visualized and measured at these sites in healthy adult subjects. Furthermore, our results show correlations between BMI and some diameters and surface areas of the nerves. There seem to be no significant differences in these parameters based on subject gender or side of the body. Given the relatively small sample in our study, further data are required to confirm these correlations. REFERENCES 1. Stewart JD. Compression and entrapment neuropathies. In: Dyck PJ, Thomas PK, editors. Peripheral neuropathy, 3 rd edn. Philadelphia: Saunders; p Graif M, Seton A, Nerubali J, et al. Sciatic nerve: sonographic evaluation and anatomic-pathologic considerations. Radiology 1991;18: Heinemeyer O, Reimers CD. Ultrasound of radial, ulnar, median and sciatic nerves in healthy subjects and patients with hereditary motor and sensory neuropathies. Ultrasound Med Biol 1999;25: Fornage BD. Peripheral nerves of the extremities: imaging with US. Radiology 1988;167: Silvestri E, Martinoli C, Derchi LE, et al. Echotexture of peripheral nerves: correlation between US and histologic findings and criteria to differentiate tendons. 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