Horner syndrome results from disruption of the sympathetic pathway that runs from the hypothalamus to the eye. Classic signs include miosis, ptosis, and anhidrosis of the affected side.
Causes include brain tumor, brain stem infarct, pancoast tumor, cervical adenopathy, skull and neck trauma, carotid dissection, and thoracic aortic aneurysm.
Instilling cocaine or apraclonidine drops into both eyes can confirm the diagnosis of Horner syndrome. Imaging studies such as MRI, CT, or MRA may be obtained based on the history and physical exam. Treatment depends on the underlying cause of Horner syndrome.