[Horner's syndrome -- update on neuroanatomy, topographic diagnosis and etiology]

Due to the complex neuroanatomy of the sympatho-excitatory pathway, Horner's syndrome represents a clinical sign that may result from a variety of lesions in the central and peripheral nervous system. The purpose of the present communication is to help the reader to localize the site of the lesion and to demonstrate the most common etiologic mechanisms resulting in Horner's syndrome. The functional anatomy of the sympathetic supply to the iris, eyelids, facial sweat glands and blood vessels is reviewed and in particular the structure of the central pathway updated. Moreover, pharmacological testing and tests of sudomotor function are described that may help to guide the decision regarding useful additional diagnostic, especially neuroimaging procedures. Finally, a schematic overview is given on the most common pathology, considering additional clinical signs and symptoms.