Susceptibility of the genitofemoral and lateral femoral cutaneous nerves to complications from lumbar sympathetic blocks: is there a morphological reason?

BACKGROUND Interference with the function of the genitofemoral nerve (GFN) and lateral femoral cutaneous nerve (LFCN) represents a significant complication of lumbar sympathetic blocks (LSBs). The nerve topography of the lumbar sympathetic trunk (LST) was investigated to find a possible morphological reason for this. METHODS A total of 118 cadavers embalmed by Thiel's method were investigated. The nerves were dissected from their innervation area to their paravertebral origins. Distances of the GFN and the LFCN to the LST were measured at levels L2/3, L3/4, and L4/5, which are the most common levels for LSB. RESULTS Two hundred and thirteen sides were assessable for the GFN and 151 sides for the LFCN. In 186 cases, the whole GFN (in 20 cases, its femoral branch only) approached the medial margin of the psoas major (PM) and passed the LST laterally at the level of L3/4 and a distance of 0-28 mm (mean distance 8.5 mm; sd 6.7 mm) and ran dorsally between the PM and the vertebral body of L3, reaching the intervertebral foramen L2/3. In three cases, the GFN fused with the LFCN. In 55 cases, the GFN-LST distance was 0-13 mm at L4/5 and in 19 cases, 9-19 mm at L2/3. The LFCN approached the lateral margin of the PM and entered the intervertebral foramen at L2/3 in 141 cases. CONCLUSIONS There is a higher risk of LSB affecting the GFN at L3/4 or L4/5 during neurolysis of the LST due to its topography. The LFCN rarely shows a strong relation to the LST and only when fused with the GFN.