The lumbar sympathetic trunk: its visibility and distance to two anatomical landmarks

The lumbar sympathetic trunk's (LST) distance to two anatomical landmarks, the costal process and medial margin of the psoas muscle, was assessed due to its use as landmarks for lumbar sympathetic blocks: the costal process for fluoroscopic guided techniques and the psoas major for CT- and MRI-guided techniques. Based on the measurements, we evaluate the trunk's visibility in MR and CT images for accurate positioning of the needle.

A total of 54 cadavers embalmed with Thiel's method were investigated. The LST's distances to the psoas major's medial margin and to the base of the lumbar vertebrae's costal process were measured on the levels L2/3, L3/4 and L4/5. The measurements were compared to MR and CT images of 20 anonymous patients to identify the LST.

LST's mean distance to the psoas major was 0.3 mm at L2/3, 3.1 mm at L3/4 and 4.6 mm at L4/5. The mean distance to the costal process was 31 mm at L2/3, 34 mm at L3/4 and 32.6 mm at L4/5. In both MR and CT imaging, a structure could be determined as the LST correlating to the measurements with decreasing possible identification from cephalad to caudad levels.

The costal process is a usable landmark for fluoroscopic guidance and the psoas major for CT- and MRI-guided techniques. The LST is clearly visible in MR and CT images, which gives both techniques a decisive advantage over fluoroscopy concerning the block of the LST due to a visible target.