Sacral plexus: optimal imaging planes for MR assessment.

Abstract

To identify the optimal imaging planes for magnetic resonance (MR) evaluation of the sacral plexus (SP) and proximal sciatic nerve (SN). The SPs of 10 health adult volunteers were prospectively studied with T1-weighted MR imaging with custom-built pelvic phased-array coils. The conspicuity of 12 anatomic characteristics (comprising the SP and their relationship to normal pelvic anatomy) on a series of coronal, axial, and oblique images was graded. Results were evaluated with the Kruskal-Wallis and Wilcoxon signed rank tests. At least two planes were necessary to assess the anatomy of the SP and SN. Analysis of average conspicuity scores showed that the direct coronal and direct axial planes were the best overall and were superior to other imaging planes in the demonstration of the L-4 and L-5 ventral rami, the lumbosacral trunk, the S-1 contribution to the SN, and the SN in the greater sciatic foramen. The sacral coronal plane was best for the visualization of the bony sacrum, sacral foramina, and proximal S-1 to S-4 nerve roots. The remaining imaging planes had limited utility. MR imaging with a combination of direct coronal and direct axial planes enables thorough evaluation of all components of the SP and proximal SN.