What is the anatomy relevant to Horner syndrome?

Updated: May 01, 2019
  • Author: Christopher M Bardorf, MD, MS; Chief Editor: Edsel Ing, MD, MPH, FRCSC  more...
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Sympathetic innervation to the eye consists of a 3-neuron arc. First-order central sympathetic fibers arise from the posterolateral hypothalamus, descend uncrossed through the midbrain and pons, and terminate in the intermediolateral cell column of the spinal cord at the level of C8-T2 (ciliospinal center of Budge). Second-order preganglionic pupillomotor fibers exit the spinal cord at the level of T1 and enter the cervical sympathetic chain, where they are in close proximity to the pulmonary apex and the subclavian artery.

The fibers ascend through the sympathetic chain and synapse in the superior cervical ganglion at the level of the bifurcation of the common carotid artery (C3-C4). Postganglionic pupillomotor fibers exit the superior cervical ganglion and ascend along the internal carotid artery. Shortly after the postganglionic fibers leave the superior cervical ganglion, vasomotor and sudomotor fibers branch off, traveling along the external carotid artery to innervate the blood vessels and sweat glands of the face.

The third-order pupillomotor fibers ascending along the internal carotid artery enter the cavernous sinus. The fibers then leave the carotid plexus briefly to join the abducens nerve (cranial nerve [CN] VI) in the cavernous sinus and enter the orbit through the superior orbital fissure along with the ophthalmic branch (V1) of the trigeminal nerve (CN V) via the long ciliary nerves. The long ciliary nerves then innervate the iris dilator and the Müller muscle.

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