Horner Syndrome



  • Horner syndrome is a constellation of neurological signs and symptoms manifested as a classic triad of ipsilateral miosis, eyelid ptosis, and anhidrosis of the ipsilateral face and/or neck (with iris heterochromia in children).
  • It is caused by the interruption of sympathetic nervous system innervation to the head, neck, and eye.
  • System(s) affected: nervous, skin/exocrine
  • Synonym(s): Bernard-Horner syndrome; Bernard syndrome; Horner syndrome; cervical sympathetic syndrome; oculosympathetic syndrome; oculosympathetic paralysis; oculosympathetic deficiency; oculosympathetic paresis


  • Predominant age: none
  • Predominant sex: male = female


  • Estimated incidence of pediatric Horner syndrome is 1.42 per 100,000 in patients younger than 19 years of age, with a birth prevalence of 1 in 6,250 for those with congenital onset of Horner syndrome.
  • Incidence in adults is not known.


Etiology and Pathophysiology

  • Oculosympathetic pathway anatomy:
    • First-order neuron: Sympathetic nerve fibers originate in the hypothalamus, descend through the brainstem, and synapse at the ciliospinal center (of Budge-Waller) located at approximately the C8–T2 levels of the spinal cord.
    • Second-order neuron: exits the spinal column, arches over the apex of the lung and under the subclavian artery, ascending to the superior cervical ganglion at the level of the carotid bifurcation and angle of the jaw (C2)
    • Third-order neuron: ascends along the adventitia of the internal carotid artery, through the cavernous sinus in proximity to cranial nerve (CN) VI and the trigeminal ganglion, and joins the nasociliary branch of CN V1 to enter the orbit—innervating the iris dilator muscle, Müller muscle in the upper eyelid, and inferior retractors in the lower eyelid.
  • A lesion affecting the neurons in the sympathetic chain (first, second, or third order) may produce signs and symptoms of Horner syndrome as a result of a lack of sympathetic input to the orbit.
    • Ptosis: Sympathetic innervation to the Müller muscle in the upper eyelid and the lower eyelid retractors helps to maintain normal eyelid position. When sympathetic innervation to these structures is interrupted, a subtle ptosis of both the upper lid (ptosis) and lower lid (reverse ptosis) may result. This ptosis may be subtle, often 2 mm or less.
    • Meiosis: The radially oriented pupillary dilator muscle produces pupillary dilation in response to stimulation by the sympathetic nervous system. Aniscoria will be more pronounced in dim lighting, reflecting impairment of dilation in the affected eye. The affected eye will constrict normally in response to light but will be slower to dilate than the unaffected pupil.
    • Anhidrosis: When present, anhidrosis may assist in localizing a lesion. Sympathetic fibers innervating sweat glands of the lower face and vasodilatory muscles branch off before the superior cervical sympathetic ganglion and travel along the external carotid artery. Lesions affecting primary and secondary neurons are more likely to produce anhydrosis of both the upper and lower face.
  • Etiologies of Horner syndrome are best classified by which neuron in the sympathetic chain is affected (first/second/third order) and by age (pediatric vs. adult).
  • Etiologies in adults:
    • First-order neuron lesions located in hypothalamus/brainstem (lateral medulla)/spinal cord (cervico-thoracic) include:
      • Arnold-Chiari malformation, basal meningitis (e.g., syphilis), cerebral vascular accident: lateral medullary (Wallenberg) syndrome, cervical cord trauma, cervical spondylosis, demyelinating disease (multiple sclerosis), Intrapontine hemorrhage, neck trauma, syringomyelia/syringobulbia, tumor (basal skull, pituitary), unintended subdural placement of lumbar epidural catheter
    • Second-order neuron pulmonary or cervico-thoracic lesions include:
      • Aneurysm/dissection of aorta, central venous catheterization, chest tubes, 1st rib fracture, lymphadenopathy (Hodgkin, leukemia, tuberculosis, sarcoid), mandibular tooth abscess, neuroblastoma, Pancoast tumor or infection of lung apex, proximal common carotid artery dissection, thoracic outlet obstruction (cervical rib, subclavian artery aneurysm), trauma/surgical injury, tumor (thyroid, mediastinum)
    • Third-order neuron lesions located in superior cervical ganglion, internal carotid artery, skull base, cavernous sinus, or orbit include:
      • Carotid cavernous fistula or other pathology, carotid endarterectomy or carotid artery stenting, cluster headaches/paroxysmal hemicrania, internal carotid artery dissection, herpes zoster, lesions of the middle ear (acute otitis media), Lyme disease, tumor (nasopharyngeal, pituitary, paratrigeminal, metastasis, skull base), tonsillectomy, trauma/surgical injury, raeder paratrigeminal syndrome
  • Etiologies in children:
    • Birth trauma/neck trauma (injury to the brachial plexus)—most common. Brainstem glioma, neuroblastoma, vascular anomalies, surgical interventions in the neck/chest, Idiopathic

Rare autosomal dominant inheritance

Risk Factors

  • Recent trauma to the head/neck/thorax (e.g., motor vehicle accidents)
  • Smoking (Pancoast tumor)
  • Known aneurysm of the carotid or subclavian arteries
  • Known malignancy/tumor/mass
  • Previous surgery (Neck/thoracic)
  • Previous instrumention of the head/neck/thoracic regions (chest tube, central venous catheterization)
  • Cluster headache

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