HORNER'S SYNDROME - A nerve condition which involves a dropping eyelid (ptosis), constricted pupil, and lack of sweating on one side of the face. Often seen in association with injury (e.g. neck fracture, penetrating injury) to the cervical sympathetic nerve trunk in the neck. Compression on the nerve trunk due to a tumor (e.g. Pancoast tumor, leukemia, lymphoma) can also manifest with this disorder. Neuroblastoma may cause this condition.