[Magnetic resonance of the brachial plexus: anatomy and study technique].

Brachial plexopathies are a common diagnostic problem: conventional imaging techniques can be useful in the detection of associated conditions (Pancoast tumors, first rib or clavicle fractures, etc.) but they cannot visualize brachial plexus structures directly. Also Computed Tomography (CT) is limited in the study of the retroclavicular region because of the artifacts due to the presence of the humeral heads in the slice. CT myelography exhibits very high accuracy in posttraumatic brachial plexopathies but fails to reveal the postganglionic plexus. In contrast, Magnetic Resonance Imaging (MRI) allows the direct detection of the brachial plexus, from spine to axilla, thanks to its multiplanarity and high contrast resolution. However, MR images are so rich in anatomical details (particularly on the oblique planes) that sometimes they become very difficult to interpret. To better define the anatomical relationships of the brachial plexus and to assess the best planes to study its different portions, 9 healthy volunteers were examined with MRI and MR images were compared with anatomical drawings and frozen cadaver sections. MRI depicts the brachial plexus from its origin to the axilla, but none of the investigated planes is sufficient, alone, to study the whole plexus adequately. The paraganglionic portion is clearly depicted on oblique sagittal images, while coronal and sagittal images are more useful for primary trunks and spinal nerves; the distal portion is perfectly visualized on sagittal images. Thus, we conclude that different examination protocols are necessary for every specific plexus portion, which means that brachial plexus MRI must be performed to try to solve a specific question by the orthopedic surgeon or the clinician.