Table 1: Neuroanatomical features of Horner syndrome-related three-neuron sympathetic pathway.

Neuroanatomy	Anatomical features of the three-neuron sympathetic pathway
First-order neuron	Descends caudally from the hypothalamus to the first synapse, which is located in the cervical spinal cord (levels C8-T2) and is also called ciliospinal center of Budge.
Second-order neuron	Travels from the sympathetic trunk, through the brachial plexus, and over the lung apex. It then ascends to the superior cervical ganglion, which is located near the angle of the mandible and the bifurcation of the common carotid artery.
Third-order neuron	Ascends within the adventitia of the internal carotid artery, through the cavernous sinus, where it is in close relation to the sixth cranial nerve. The oculo-sympathetic pathway then joins the ophthalmic (V1) division of the fifth cranial nerve (trigeminal nerve).