Horner syndrome is caused by damage to the sympathetic nerves of your face and eyes. Sympathetic nerves control your body's circulation and sweating. Depending on where the nerves are damaged, Horner syndrome is often classified in two groups.


Sympathetic nerves in your face start in an area of your brain known as the hypothalamus, travel through the brainstem and then down your spinal cord to enter your chest. This is the first half of their "route." Possible causes of nerve damage in this area are:

  • Stroke (usually a cerebral infarction or most commonly a brainstem location)
  • Tumor
  • Syringomyelia — a condition in which a fluid-filled cyst (syrinx) develops within your spinal cord
  • Cluster headaches


From your chest, your sympathetic nerves go back up your neck, next to the main arteries that deliver blood to your head (carotid arteries), into your skull and then to your eyes. Nerve damage in this area may be caused by:

  • Spinal cord injury
  • A tear in the inner lining of one of your carotid arteries (carotid artery dissection)
  • An injury to a baby during birth
  • Lung cancer in the apex of the lung

Although Horner syndrome may be a sign of one of these conditions, in some situations, a specific cause can't be found. This is known as idiopathic Horner syndrome.

Apr. 16, 2011