Ultrasound imaging of small peripheral nerves - a primer for radiologists

High-resolution imaging has transformed the evaluation of small superficial peripheral nerves, enabling earlier detection of neuropathies, traumatic injuries, and entrapments. Among available modalities, ultrasound is particularly well suited for this purpose owing to its high spatial resolution, dynamic assessment capabilities, and ability to guide interventions. Normal nerves can be recognized on ultrasound by their fascicular architecture and characteristic honeycomb appearance, which helps distinguish them from adjacent tendons, vessels, and connective tissue. High-frequency transducers allow improved delineation of fascicular detail, while small-footprint probes enable imaging of nerves in anatomically constrained regions, establishing ultrasound as a reliable and cost-effective tool for evaluating peripheral nerve injuries. Because of spatial resolution limitations, magnetic resonance imaging has restricted ability to evaluate submillimeter-sized nerves; high-resolution ultrasound is therefore particularly effective in localizing pathological nerves - both in terms of the exact site of involvement and the length of the affected segment. This review article highlights in detail the sonographic techniques, pitfalls, and key anatomic landmarks for visualizing small peripheral nerves in the upper and lower extremities, with particular emphasis on nerves that are frequently under-evaluated in routine clinical practice yet often contribute to allodynia. Normal anatomical appearance on ultrasound is provided for better understanding along with examples of pathologies affecting these nerves.