= syndrome ← interruption of oculosympathetic pathway:

• ipsilateral blepharoptosis; pupillary miosis; facial anhidrosis

Oculosympathetic pathway:

1. 1^st order neuron: posterolateral hypothalamus → brainstem → intermediolateral column of spinal cord → exit at C8, T1, T2
2. 2^nd order preganglionic neuron: ventral spinal root → arch over apex of lung → cervical sympathetic chain → superior cervical ganglion
3. 3^rd order postganglionic neuron: with carotid artery → cavernous sinus → ophthalmic branch of cranial nerve V

1. CENTRAL HORNER (uncommon)
   Location: hypothalamus, thalamus, brainstem, cervical cord
   Cause: infarction of PICA / distal vertebral artery
   • hypothalamic / brainstem / spinal cord signs
2. PREGANGLIONIC HORNER
   Location: cervicothoracic cord, brachial plexus, anterior neck, mediastinum
   Cause: trauma, lung (Pancoast) / mediastinal tumor, lesion in cervical spinal cord / brachial plexus
3. POSTGANGLIONIC HORNER
   Location: superior cervical ganglion, internal carotid artery, cavernous sinus, orbital apex
   Cause: ICA dissection / aneurysm, carotid-cavernous fistula / thrombophlebitis, inflammation (Tolosa-Hunt syndrome), skull base tumor