[Sonography of peripheral nerves--first part: upper limb]

At sonography, peripheral nerves have a fibrillar appearance, that is tape-like on longitudinal scans and ovoid on transverse scans. Nerves are composed by hypoechoic fascicules within a hyperechoic environment. Less subject to anisotropy and soft to the pressure of the probe, nerves lie between muscles, often with vessels, or within channels. Recent advances in sonographic technology allow accurate imaging of peripheral nerves of the upper and lower limbs, but adequate anatomical and clinical knowledge, as well as rigorous technique are mandatory. The purpose of this general review is to present, as clearly as possible, in two parts, the sonographic features of normal and pathological nerves of upper and lower limbs. This first part will discuss nerves of the upper limb.