Brachial plexus sonoanatomy explained by multiplanar reformatting of digitized anatomy

Abstract

Background The application of ultrasound (US) in peripheral nerve blocks has increased substantially during the last 15 years. However, this technique may have some drawbacks, one of which is the need of a high level of experience of the anaesthesiologist in performing US-guided blocks, a.o. in interpreting the cross-sections displayed in the ultrasound images. Sonoanatomical cross-sections produced by digitized anatomy are easier to understand. Methods From seven cadavers by cryomicrotomy a large series of consecutive high-resolution photographs with an interval of 0.078 mm were obtained from various regions. By multiplanar reformatting perpendicular reconstructions were made using self-developed software (E-MAC). Thus, 3-D tissue blocs were obtained with a voxel size of 78 μm that enabled the reconstruction of oblique cross-sections, in which sizes, angles and surface areas could be measured. Finally, a movie-like animation of consecutive cross-sections including a variable magnification display was built in. Results Reconstructions from the 3-D tissue blocs illustrate important sonoanatomical issues of the brachial plexus (BP). Its proximal nerve roots show varying angulations, whereas the nerves, towards distal, exhibit a shift in internal architecture and changing topography relative to the subclavian and axillary artery. Blood vessels that may hinder needle insertion are highlighted. Conclusion Multiplanar reformatting of digitized anatomy has made feasible the reconstructions of non-standard anatomical planes. The various (oblique) cross-sections explain the difference between hypo-echogenic vs hyper-echogenic structures of the BP-nerves, the position of the needle tip in the various BP-approaches, the topography of important blood vessels displayed in US images and illustrates why the US-probe needs a continuous change in angulation.