Imaging of the peripheral nerve system

Ultrasonography is a convenient and cost-effective method for examining the peripheral nerve system before more expensive imaging modalities, such as magnetic resonance, are considered. A good knowledge and familiarity with the anatomy being evaluated is essential. The choice of the imaging modality depends on the size and location of the lesion.

Ultrasound

Ultrasound of the peripheral nerves necessitates use of high frequency transducers because of the small size of the structures to be visualised; good quality ultrasound equipment is therefore necessary to achieve highresolution images. Linear transducers are preferred over curvilinear or sector transducers because of their wide superficial field of view and uniform angle of insonation. Harmonic and/or compound imaging should be used if available as it decreases artefacts and increase signal-to-noise ratio. Doppler ultrasonography is routinely used to distinguish blood vessels from nerves, and when assessing the vascularity of a structure. Ultrasound of the peripheral nerves can be completed without anaesthesia or sedation, if the patient remains still and relaxed during the ultrasound. Comparison scanning of contralateral structures is useful when a suitable anatomic reference is lacking.

On ultrasound the peripheral nerves can be recognised as hypoechoic structures surrounded by a thin hyperechoic rim and containing discontinuous hyperechoic bands. The peripheral nerves may be constituted by a single nerve unit or as a group of multiple units close together. Ultrasonographic anatomy of the brachial plexus and major nerves of the canine thoracic limb, and of the sciatic and femoral nerves has been described. [...]