Furthermore, this technique has been proved valuable Y-27632 in vitro for the examination of traumatic nerve lesions, nerve sheath tumors and several types of polyneuropathies. The most common cause of focal neuropathies is entrapment of a nerve while passing through an osseo-fibrous tunnel, such as the carpal tunnel at the wrist and the cubital tunnel at the elbow. The pathophysiological feature of nerve compression comprises disturbed vascular microcirculation, impaired axonal transport, edema within the nerve, and thickening of perineurium resulting in

an enlargement of the nerve diameter, which is typically located proximally to the entrapment site [3]. Consequently, changes in nerve cross-sectional area are the most relevant sonographic findings in entrapment neuropathies (Supplementary Fig. 1; to view the figure, please visit the online supplementary file in ScienceDirect). In patients with carpal tunnel syndrome (CTS), numerous studies demonstrated high accuracy for both, the maximum cross-sectional area of the median nerve proximal to the entrance of the carpal tunnel and the GSK1120212 nmr ratio of the median nerve area at the wrist to the area of the nerve at the forearm [4], [5], [6], [7], [8], [9], [10] and [11]. For example,

according to a cut-off value for the cross-sectional area of 10 mm2, sensitivity and specificity were 82% and 87% in a study by Ziswiler

et al. [6]. Increasing the cut-off value to 12 mm2 resulted in a 100% specificity at the expense of a lower sensitivity of 44%. Secondary findings in patients with CTS are nerve flattening within the carpal tunnel and bowing of the flexor retinaculum [2]. In contrast to electrodiagnosis, ultrasonography has the capability to rule out secondary causes of CTS such as tenosynovitis, ganglion cysts, accessory muscles or tumors [4] and [5]. In case the nerve branches proximal to the carpal tunnel, ultrasonography can further demonstrate a bifid median nerve [11] or a persistent median artery (Fig. 1) [12]. If symptoms persist or worsen after surgery, ultrasonography may be valuable to assess incomplete splitting of the retinaculum Depsipeptide or intra-operative injuries of the ulnar branch of the median nerve (Fig. 2). However, in contrast to NCS, ultrasonography is obviously not suitable for post-treatment follow-up of CTS since Lee et al. [13] pointed out that the cross-sectional area of the median nerve remained unchanged 6 months after surgery. Supplementary Fig. 1.  Cross-sectional (a) and longitudinal (b) view of the median nerve (dotted line) at the wrist in a patient with carpal tunnel syndrome. Cross-sectional area of the nerve is enlarged to 16 mm2. Arrows indicate the retinaculum flexorum.