Traumatic peripheral nerve injuries represent a spectrum of conditions and remain challenging to diagnose and prognosticate. High-resolution ultrasonography and magnetic resonance neurography have emerged as useful diagnostic modalities in the evaluation of traumatic peripheral nerve and brachial plexus injuries. Ultrasonography is noninvasive, is able to rapidly interrogate large areas and multiple nerves, allows for a dynamic assessment of nerves and their surrounding anatomy, and is cost-effective. It allows for the prompt differentiation of neurotmetic versus axonotmetic traumatic nerve injuries, which informs surgical decision making. Magnetic resonance neurography yields images of peripheral nerves with high structural resolution down to the level of fascicles, is able to evaluate difficult anatomic areas that may not be reached by ultrasonography, and can detect signs of acute and chronic muscle denervation. Advanced preclinical techniques, such as second-harmonic generation microscopy, use multiphoton microscopy to visualize the internal collagenous structure of peripheral nerves, while third-harmonic generation microscopy can image myelin. One potential future application for multiphoton microscopy is the in vivo real-time assessment of nervous tissue. Near-infrared fluorescence also has the potential to assist with intraoperative peripheral nerve identification and assessment of pathology, but many challenges remain in identifying or designing the ideal contrast agent.
