Origin of Sympathetic Fibers in the Thoracic Region

The thoracic sympathetic trunk ganglia are about the same in number as the spinal thoracic nerves; usually 11 ganglia [3]. The first thoracic ganglion is fused with the lower cervical ganglion to help form the stellate ganglion, which also stands out because of its greater size (approximately 15 mm × 7 mm) in comparison to other ganglia [1] (Figure 28.1).

Course of the Sympathetic Fibers

The pre-ganglionic fibers of the thoracic sympathetic nervous system exit the intervertebral foramen along with their respective spinal nerves. Upon its exit from the foramen, the thoracic spinal nerve gives off a recurrent branch that loops back through the foramen to supply innervation for the spinal ligaments, meninges, and corresponding vertebrae. The spinal nerve also interfaces with the thoracic sympathetic chain through the myelinated pre-ganglionic fibers of the white rami communicantes and the unmyelinated post-ganglionic fibers of the gray rami communicantes [4–8] (Figure 28.2).

Pre- and post-ganglionic fibers synapse at the level of the thoracic sympathetic ganglion. Pre-ganglionic fibers can synapse at just one ganglion or at several different ganglia and are able to ascend or descend the sympathetic chain by synapsing with ganglia situated above or below them. A post-ganglionic fiber can receive stimuli from more than one pre-ganglionic fiber [3]. Some of the post-ganglionic fibers return to their respective somatic nerves via the gray rami communicantes. These fibers supply sympathetic innervation to the vasculature, sweat glands and pilomotor muscles in the skin. Other fibers connect to specific viscera such as the cardiac plexus, crossing the sympathetic trunk and terminating in distant ganglia.

The fibers of the cervicothoracic sympathetic chain originate in the intermediolateral column at T2 to T8 levels. On reaching the sympathetic chain, these nerves ascend and synapse with sympathetic ganglia located superiorly, first in T2, then, successively, in T3, in the stellate ganglion, the medial cervical ganglia and the superior cervical ganglia.

It is worth noting that in 20% of individuals, sympathetic fibers synapse at T2 and T3 and reach the brachial plexus directly, without traversing the stellate ganglion. These are called the nerves of Kuntz and can be seen in Figure 28.3. This has led to T2 and T3 being called the key synaptic key station of the upper limbs since they promote a more specific blockade of this region [5–10].

The position of each ganglion in relation to the vertebral body changes as the ganglia course more caudad. In the neck region, the ganglia are located posterior to the carotid sheath and anterior to the transverse process of the vertebral bodies [3], while in the thorax, they are located anterior to the ribs [3], immediately lateral to the costovertebral joint process and anterior to the vessels and intercostal nerves. More specifically, the stellate ganglion is generally found above the head of the first rib [1], while the T2 ganglion is located anteriorly in the mid-section of the corresponding rib neck, but the T3 to T6 ganglia are located anteriorly to the head of their respective ribs [11].

The median location of the ganglia at T2 level is 2 mm rostral to the midpoint of the T2 vertebral body on the right side, between the head of the ribs (range 1–7 mm), and 1.5 mm rostral to the midpoint of the vertebral body (gap 1–2 mm) on the left side. The T3 ganglia are located 2 mm (range 2–3 mm) rostral to the midpoint of the T3 vertebral body, bilaterally.

The pleural space is lateral and anterior to the thoracic sympathetic chain. Given the proximity of the thoracic somatic nerves to the sympathetic chain on performing a thoracic sympathetic block, there is a likelihood of both neural pathways being blocked [3, 11–13].

Anatomic Relation Between Ribs and Their Joints

The more medial portions of the ribs include the head, neck, tubercle (joint eminence and a non-joint eminence) and curved body of the shaft and the initial portion of the costal groove.

The costal joints, along with the tubercle and the head of each rib, should be observed because they comprise the radiologic landmarks used in this technique. It should also be noted that a line drawn from the tubercle to the head of each rib is almost parallel to the neck of each rib.