Thoracic ganglia

Thoracic ganglia are a group of 12 paravertebral sympathetic ganglia which are situated in the posterior mediastinum in the thorax. These ganglia form part of the thoracic component of the sympathetic trunks, located on either side of the vertebral column.

Superiorly, the first thoracic ganglion–in 80% of cases–fuses with the inferior cervical ganglion to form a large cervicothoracic ganglion (a.k.a. stellate ganglion). Inferiorly, the twelfth thoracic ganglion is continuous with the lumbosacral ganglion. All twelve thoracic ganglia interconnect with each other via interganglionic fibers within the sympathetic trunks and also communicate with the thoracic spinal nerves via the gray and white rami communicantes.

As the thoracic sympathetic trunks descends in the posterior mediastinum, initially they lie in front of the neck of the ribs, but gradually come to lie more medially on the posterolateral aspect of the thoracic vertebral bodies, until they enter the abdomen by passing posterior to the medial arcuate ligaments or the medial crura of the diaphragm. They are positioned posterior to the costal pleura, but anterior to the intercostal vessels and nerves.

Branches from the thoracic ganglia can be grouped into two categories:

• Those arising from the upper five thoracic ganglia comprise of postganglionic fibers which provide motor autonomic innervation to various thoracic viscera.

• Those arising from the lower seven thoracic ganglia include the greater, lesser and least (or lowest) splanchnic nerves. The greater splanchnic nerve arises from the fifth to the ninth (T5 to T9) thoracic ganglia, whereas the lesser splanchnic nerve originates from tenth to eleventh (T10 to T11) thoracic ganglia, while the least splanchnic nerve emanates from the twelfth (T12) thoracic ganglion. All three splanchnic nerves course medially and ventrally, as they pierce through the crura of the diaphragm to end up synapsing in various ganglia in the prevertebral plexuses. For instance, the greater and lesser splanchnic nerves go to the coeliac and aorticorenal ganglia inside the coeliac plexus, while the least splanchnic nerve ends up in the renal ganglion in the renal plexus. Next, the postganglionic neurons reach out to various viscera for innervation and help in the motility and secretions of the gut.

Please note that all branches of thoracic ganglia described above also contain visceral afferent neuronal fibers that transmit sensory information from the viscera towards the central nervous system.