<prompt> Answer this question truthfullyWhat is Horners syndrome and what type of brain stem lesions can cause it?  <response>: <reason> Horners syndrome is a neurological condition characterized by a set of symptoms that includes drooping of the eyelid, a constricted pupil, and decreased sweating on one side of the face. Lesions in the brain stem that affect the sympathetic pathway can cause ipsi-lateral Horners syndrome. 