Background Entrapment neuropathies are the most common peripheral neuropathies and one of the main reasons for neurological care in routine practice. The electrophysiological study remains the principal tool used for diagnosis and classification of peripheral nerve dysfunction. However, it should be noted that not all patients with entrapment neuropathies have nerve conduction deficits, leading to negative results in electrophysiological testing. To address this diagnostic issue, some authors recommend the use of musculoskeletal ultrasound. The recent development of high-resolution ultrasound has enabled to achieve detailed images of the peripheral nerve structure.

Methods This review is based mainly on peer reviewed studies available in Medline. Secondarily, several publications such as books and evidence based guidelines are reviewed.

Results Ultrasound peripheral nerve can be used to evaluate the cross-sectional area, the flattening ratio, echotexture, presence of nerve intraneural flow and mobility. An increased cross-sectional area, presence of hypervascularity measured by power-doppler, changes in the fascicular pattern of nerve echogenicity and reduced nerve gliding are common pathological changes in neural entrapments. The recent development of different measurement methods allows quantification of these pathological findings. The increased cross-sectional area seems to be the most common sonographic finding in conditions such as carpal tunnel syndrome, radial neuropathy or cervical radiculopathy. These ultrasound changes significantly correlated with duration of disease. Some studies suggest that there is an inverse relationship between vascular changes observed with the power-doppler and severity of entrapment. The increased cross-sectional area seems to correlate with electrophysiological severity of entrapment neuropathy.

Conclusions Numerous studies demonstrate that peripheral nerve ultrasound has a significant complementary role with electrophysiological testing in entrapment neuropathies.