The greater splanchnic nerves are paired structures formed from preganglionic sympathetic nerve fibres which pass without synapsing through the paravertebral ganglia of segments five to nine on either side of the spinal column. The fibres from the ganglia converge to form a nerve which runs inferiorly through the thorax within the posterior mediastinum. It is closely apposed to the vertebral bodies of the spinal column. On the left, it is slightly lateral to the azygous vein. On the right, it is lateraly to the hemiazygous system and the aorta.
The greater splanchnic nerves pierce the diaphragmatic crura on both sides at the level of L1. Then, the fibres pass to onto the surface of the aorta where they synapse with postganglionic fibres within the coeliac ganglia.