Horner Syndrome

Horner syndrome can be caused by a lesion anywhere along the oculosympathetic pathway. Although there may be other signs that help with localization of the lesion, the syndrome often occurs in isolation. In this chapter, we begin by reviewing the anatomy of the oculosympathetic pathway. We next describe the clinical features of Horner syndrome, which include ipsilateral miosis and eyelid ptosis. We then discuss the role and potential pitfalls of pharmacologic pupil testing in the diagnostic evaluation of Horner syndrome. We review the potential causes for Horner syndrome, with a focus on causes for acute isolated painful Horner syndrome, such as internal carotid artery dissection. Lastly, we discuss the workup, management, and potential complications of internal carotid artery dissection.