The superior cervical ganglion is the largest sympathetic ganglion in the body, approximately 2.5 cm long, lying posterior to the internal carotid artery and anterior to the longus capitis and longus colli muscles at the C2-C3 level. It receives preganglionic fibres from the upper thoracic spinal cord via the cervical sympathetic trunk, and sends postganglionic fibres via the internal and external carotid arteries to innervate the entire head and face with sympathetic supply including the dilator pupillae, superior tarsal muscle, facial sweat glands, and blood vessels.
Injury to the superior cervical ganglion or the postganglionic sympathetic fibres leaving it produces a complete postganglionic Horner syndrome (ipsilateral miosis, ptosis, anhidrosis of the entire ipsilateral face) since the external carotid-distributed facial sympathetics as well as the internal carotid fibres are all interrupted at this level. The ganglion is at risk during radical neck dissection and from tumours in the carotid space and skull base. Superior cervical ganglion block at C2-C3 is performed for head and neck pain, cluster headache, and atypical facial pain.
Tumour infiltration, neck dissection, or trauma at the superior cervical ganglion level produces a complete postganglionic Horner syndrome with miosis, ptosis, and anhidrosis of the entire ipsilateral face (distinguishing it from the partial anhidrosis of preganglionic lesions), diagnosed pharmacologically with cocaine and hydroxyamphetamine testing.
Injection of local anaesthetic at the C2-C3 level targeting the superior cervical ganglion blocks sympathetic outflow to the head and face, used therapeutically for cluster headache, atypical facial pain, complex regional pain syndrome of the head, and as a diagnostic test to confirm sympathetically maintained pain.
