MRI of the brachial plexus

Magnetic resonance (MR) is the investigation of choice in studying the anatomy of the brachial plexus given its wide range of features: scanning on all spatial planes essential because of the oblique path of the plexus, high intrinsic contrast between different structures identifying the position of the plexus; high spatial resolution necessary to display the tiny nerve roots. The brachial plexus was investigated in 15 healthy subjects aged between 17 and 53 years. Two series of T1-weighted SE sequences were performed on the sagittal plane positioned separately over the whole stretch of the plexus. Further sequences included T2-weighted TSE axial scans, T2-weighted TSE scans with fat signal suppression (MR neurography), T1-weighted SE coronal scans and T1-weighted TurboFieldEcho coronal scans. T1-weighted SE scans offered the most information as the brachial plexus is constantly related to the subclavian vessels on this plane and can be identified by the hyperintensity of its surrounding fat tissue. For accurate identification of the main branches of the plexus, we divided sagittal scans into five contiguous mediolateral levels. The first level identifies the emergence of the nerve roots from the root canals; the second corresponds to a section over the scalenus muscles, the third level is over the supraclavicular triangular space; the fourth comprises the sections over the axilla and the fifth corresponds to a more lateral plane through the pectoralis muscles. The three primary trunks, superior, middle and inferior, can be identified in the second level, constantly positioned above and behind the subclavian vessels and clearly identified by the hyperintensity of the adipose tissue. The primary trunks divide into the anterior and posterior rami in level three and in level four the nerve branches surround the subclavian vessels running in a joint sheath. The fifth level contains the secondary lateral, middle and posterior trunks. The coronal plane positioned obliquely depending on the orientation of the plexus, will identify the emergence of the roots from the spine and their initial stretch partly visible on the coronal plane. The nerve branches appear slightly hyperintense in T2-weighted sequences with fat signal suppression and these scans are useful in studying plexus pathology. High field intensity systems (1.5T) and phased array surface coils gave good spatial resolution. In the near future, multiple dedicated surface coils will be available for MR study of the brachial plexus, thereby improving the spatial resolution and the signal-to-noise ratio, essential factors in identifying small structures like the peripheral nerve branches.