Sympathetic trunk

Truncus sympathicus

Also known as: sympathetic chain, paravertebral ganglia, stellate ganglion, superior cervical ganglion, ganglion impar

A paired chain of interconnected paravertebral sympathetic ganglia running alongside the vertebral column from the base of the skull to the coccyx. It distributes sympathetic fibres to every spinal nerve, to the head, and to the thoracic viscera.

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Overview

Ganglia per side≈21–23 (3 cervical, 11–12 thoracic, 4 lumbar, 4–5 sacral) + ganglion impar

White ramiT1–L2 only

Grey ramiAll 31 spinal nerves

Preganglionic neurotransmitterAcetylcholine (nicotinic receptors)

Postganglionic neurotransmitterNoradrenaline (ACh to sweat glands)

Each trunk lies just lateral to the vertebral bodies and contains about 21–23 ganglia:
• 3 cervical: superior, middle and inferior;
• 11–12 thoracic, over the heads of the ribs;
• 4 lumbar, along the medial border of psoas;
• 4–5 sacral, medial to the anterior sacral foramina.

The two trunks unite in front of the coccyx at the single ganglion impar. In about 80% of people the inferior cervical ganglion fuses with the first thoracic ganglion to form the cervicothoracic (stellate) ganglion. It lies in front of the neck of the first rib and the C7 transverse process, behind the vertebral artery, close to the dome of the pleura.

Preganglionic sympathetic neurons live only in the lateral horn (intermediolateral cell column) of T1–L2. Their myelinated axons leave in the ventral roots and enter the trunk through white rami communicantes, which are present only at T1–L2. A preganglionic fibre then has three options:
1. synapse in the ganglion at the same level;
2. ascend or descend in the trunk and synapse at another level, which is how the cervical and lower lumbar/sacral ganglia receive input;
3. pass through without synapsing as a splanchnic nerve to a prevertebral ganglion or to the adrenal medulla.

Unmyelinated postganglionic axons return to every one of the 31 spinal nerves through grey rami communicantes, supplying the sweat glands, arrector pili muscles and blood vessels of each dermatome. The cervical ganglia send postganglionic fibres along the carotid and vertebral arteries to the head. The cervical and upper thoracic (T1–T5) ganglia also give cardiopulmonary splanchnic nerves to the cardiac and pulmonary plexuses.

Location: Paravertebral, from the base of the skull (superior cervical ganglion at C2–C3) to the coccyx (ganglion impar), anterolateral to the vertebral bodies and behind the parietal pleura and peritoneum.

Parts & subdivisions

Superior cervical ganglion
The largest ganglion of the trunk (about 2.5 cm), at the level of C2–C3. It supplies the whole head through plexuses along the internal and external carotid arteries, including the dilator pupillae, the superior tarsal (Müller) muscle, and the facial sweat glands and vessels. It also helps regulate melatonin secretion by the pineal gland.
Stellate (cervicothoracic) ganglion
The fused inferior cervical and first thoracic ganglia, lying anterior to the neck of the 1st rib and the C7 transverse process. A stellate ganglion block is used for complex regional pain syndrome of the upper limb, refractory ventricular arrhythmias and vascular insufficiency. A successful block produces an ipsilateral Horner syndrome.
White vs grey rami
White rami carry myelinated preganglionic fibres from spinal nerve to trunk and are found only at T1–L2. Grey rami carry unmyelinated postganglionic fibres from trunk to spinal nerve and are found at all levels.
Ganglion impar
The single coccygeal ganglion where the two trunks meet, in front of the sacrococcygeal junction. It is a target for nerve blocks in chronic perineal and coccygeal pain.

Anatomy

Innervation

Postganglionic sympathetic supply to:
• the skin of the whole body (sweat glands, arrector pili, cutaneous vessels);
• the blood vessels of the limbs and trunk;
• the head and neck (pupil, eyelid, glands, vessels);
• the heart and lungs.

It also relays preganglionic fibres to the abdominopelvic viscera via the splanchnic nerves.

Nerve roots

Preganglionic input from spinal segments T1–L2 (white rami); postganglionic output to all spinal nerves (grey rami).

Branches

- Grey rami communicantes: to all spinal nerves.
• Superior cervical ganglion: the internal carotid plexus (to the eye, the dilator pupillae and superior tarsal muscle, and the lacrimal and salivary vessels), the external carotid plexus (facial sweat glands and vessels), and branches to the cardiac plexus.
• Middle and inferior (stellate) cervical ganglia: cardiac nerves, and the vertebral plexus.
• Thoracic ganglia: cardiopulmonary splanchnic nerves (T1–T5); the greater, lesser and least splanchnic nerves (T5–T12).
• Lumbar ganglia: lumbar splanchnic nerves (L1–L2).
• Sacral ganglia: sacral splanchnic nerves (to the inferior hypogastric plexus).

Function

Relay station for sympathetic outflow from T1–L2 to the whole body
Thermoregulatory sweating and cutaneous vasoconstriction in every dermatome
Sympathetic control of the pupil, eyelid and facial vessels (head)
Increase of heart rate and contractility; bronchodilation (via cardiopulmonary nerves)
Conduit for visceral afferents (pain) from the thoracic and abdominal organs

Clinical significance

Horner syndrome

Interruption of the three-neuron oculosympathetic pathway causes ipsilateral:
• ptosis (mild, from loss of Müller muscle);
• miosis with dilation lag;
• anhidrosis of the face;
• apparent enophthalmos.

The pathway and its typical lesions:
1. First-order neuron: hypothalamus → brainstem → ciliospinal centre of Budge (C8–T2). Lesions here include lateral medullary syndrome and syringomyelia.
2. Second-order (preganglionic) neuron: leaves in the T1 ventral root, ascends in the trunk over the lung apex to the superior cervical ganglion. Lesions here include a Pancoast tumour, cervical rib, Klumpke palsy and neck surgery.
3. Third-order (postganglionic) neuron: runs from the superior cervical ganglion along the internal carotid artery (through the cavernous sinus, then via the nasociliary and long ciliary nerves) to the dilator pupillae and Müller muscle. A key lesion is carotid dissection, which typically gives a painful Horner syndrome.

The sudomotor fibres to the face follow the external carotid artery, so a third-order lesion causes little or no anhidrosis.

Sympathectomy

Endoscopic thoracic sympathectomy at T2–T3 treats severe palmar hyperhidrosis. Compensatory sweating elsewhere is a common side-effect. Lumbar sympathectomy was formerly used for peripheral vascular disease.

Test yourself

A smoker has ptosis and a constricted pupil on the left with a dry left side of the face. Chest X-ray shows a left apical mass. Which structure is affected?

Left oculomotor nerve
Cervicothoracic sympathetic chain (preganglionic fibres from T1)
Left facial nerve
Edinger–Westphal nucleus

Answer: Cervicothoracic sympathetic chain (preganglionic fibres from T1)

A Pancoast tumour at the lung apex interrupts the second-order (preganglionic) oculosympathetic fibres, causing Horner syndrome. A CN III lesion would cause a complete ptosis with a dilated pupil.