The brachial plexus: Normal anatomy, pathology, and MR imaging

High-resolution MR imaging of peripheral nerves and nerve plexuses is an area of rapidly growing clinical interest and importance. The number of studies performed is rapidly increasing in response to the need for more detailed in vivo information about neuropathic changes and regional neural anatomy before treatment planning by peripheral nerve specialists [84]. Specific information gained from peripheral nerve-imaging studies is being used to determine the need for biopsy or surgical treatment. In patients who have small tumors, peripheral nerve imaging has proved useful in planning the surgical approach and in predicting the prognosis for preservation of nerve function postoperatively. In cases of traumatic nerve injury, MR imaging results are being considered as part of the clinical assessment regarding (1) the likelihood of spontaneous recovery versus the need for surgical repair and (2) the progression of nerve recovery postoperatively. Additional applications and new developments for the MR techniques used in peripheral nerve imaging are on the horizon. Among these are improvements in the homogeneity of fat saturation methods and alternative approaches to removing fat signal, such as multipoint Dixon fat-water separation with SSFP or FSE imaging methods. Rapid volumetric data acquisition with high CNR may allow the presentation of the largest peripheral nerves and their branches in a three-dimensional display, analogous to the three-dimensional maximum-intensity projection images of the vasculature available with MR angiography. This presentation will provide the referring physician with a more complete picture of the affected peripheral nerves, facilitating localization and diagnosis of peripheral neuropathy. Improvements in imaging of peripheral nerves coupled with the availability of MR-guided interventional systems should eventually lead to therapeutic interventions for peripheral neuropathy. Experimental studies using mice already have shown that the introduction of replication-defective viral vectors directly into dorsal root ganglia using microneurosurgical technique leads to long-term expression of reporter genes along the length of the sensory neuron, from its distal portion to the ipsilateral nucleus gracilis and cuneatus [85]. Dorsal root ganglia injection may be superior to other therapeutic approaches, such as intraneural injection into more distal peripheral nerve segments [86]. Targeted expression of foreign genes in the peripheral nervous system has several potentially valuable applications, including gene therapy of neuromuscular diseases, neuroanatomic studies, and the elucidation of mechanisms of axonal flow.