The cervical sympathetic trunk is the superior continuation of the thoracic sympathetic chain, ascending on the prevertebral fascia deep to the carotid sheath. It bears three ganglia: the superior cervical ganglion (opposite C1-C3, the largest sympathetic ganglion in the body), the middle cervical ganglion (opposite C6, variable), and the inferior cervical ganglion (which fuses with the T1 ganglion to form the stellate ganglion at C7-T1). The chain supplies all sympathetic innervation to the head, neck, and upper limb.
The cervical sympathetic trunk lies immediately posterior to the carotid sheath contents and is vulnerable during carotid endarterectomy, anterior cervical spine surgery, radical neck dissection, and thyroid surgery. Injury produces Horner syndrome (ptosis, miosis, anhidrosis) from interruption of the sympathetic supply to the face and eye. The superior cervical ganglion is the largest ganglion; its injury produces a more complete Horner with anhidrosis of the entire ipsilateral face, distinguishing a preganglionic from a postganglionic lesion.
The cervical sympathetic trunk immediately posterior to the carotid artery is at risk during carotid endarterectomy and internal carotid aneurysm repair, with injury producing Horner syndrome characterised by ptosis, miosis, and ipsilateral facial anhidrosis; most resolve within weeks but some are permanent.
The pattern of anhidrosis in Horner syndrome localises the lesion level: involvement of the superior cervical ganglion or above produces facial anhidrosis, while a lesion below the ganglion (postganglionic) spares facial sweating since the external carotid carries the facial sympathetics separately from the internal carotid territory.
