Muscle denervation and nerve entrapment syndromes.

Nerve entrapment and muscle denervation syndromes are often hard to diagnose, presenting as pain or unusual weakness. In addition many of the clinically named syndromes are poorly defined and understood. An understanding of the clinical signs, the normal and variant anatomy, and the often variable relationship between the imaging findings and the clinical findings is essential in the accurate diagnosis and management of these disorders. MRI has proved sensitive to the presence of muscle denervation and can provide high resolution imaging along the course of the major nerves allowing demonstration of mass lesions or normal anatomical variations. The diagnosis of nerve entrapment and muscle denervation syndromes can be a substantial clinical challenge. Imaging, particularly MRI, can prove very useful in confirming a nerve lesion by demonstrating changes of muscle denervation. Identification of the muscles involved combined with knowledge of the normal patterns of innervation and their variations can allow localization of the site of the nerve lesion.