Quantitative Architecture of the Brachial Plexus and Surrounding Compartments, and Their Possible Significance for Plexus Blocks

Abstract

Background Nerve injury after regional anesthesia of the brachial plexus (BP) is a relatively rare and feared complication that is partly attributed to intraneural injection. However, recent studies have shown that intraneural injection does not invariably cause neural injury, which may be related to the architecture within the epineurium. A quantitative study of the neural components and the compartment outside BP was made. Methods From four frozen shoulders, high-resolution images of sagittal cross-sections with an interval of 0.078 mm were obtained using a cryomicrotome to maintain a relatively undisturbed anatomy. From this data set, cross-sections perpendicular to the axis of the BP were reconstructed in the interscalene, supraclavicular, midinfraclavicular, and subcoracoid regions. Surface areas of both intraepineurial and connective tissue compartments outside the BP were delineated and measured. Results The nonneural tissue (stroma and connective tissue) inside and outside the BP increased from proximal to distal, being significant between interscalene/supraclavicular and midinfraclavicular/subcoracoid regions (P < 0.001 for tissue inside BP, P < 0.02 for tissue outside BP). The median amount of neural tissue remained approximately the same in the four measured regions (41.1 +/- 6.3 mm; range, 30-60 mm). The ratio of neural to nonneural tissue inside the epineurium increased from 1:1 in the interscalene/supraclavicular to 1:2 in the midinfraclavicular/subcoracoid regions. Conclusion Marked differences in neural architecture and size of surrounding adipose tissue compartments are demonstrated between proximal and distal parts of the brachial plexus. These differences may explain why some injections within the epineurium do not result in neural injury and affect onset times of BP blocks.