| Central (first order) | | Hypothalamus | | Stroke | | Tumor | | Brainstem (lateral medulla) | | Stroke | | Demyelination | | Tumor | | Spinal cord (cervicothoracic) | | Trauma | | Tumor (intramedullary) | | Myelitis | | Syringomyelia | | Demyelination | | Arteriovenous malformation | | Infarction | | | Preganglionic (second order) | | Pulmonary apical lesions | | Subclavian artery aneurysm | | Apical lung tumor (Pancoast tumor) | | Mediastinal tumors | | Cervical rib | | Iatrogenic (jugular cannulation, chest tube placement, thoracic surgery) | | Thyroid malignancies | | | Postganglionic (third order) | | Superior cervical ganglion | | Trauma | | Jugular venous ectasia | | Iatrogenic (surgical neck dissection) | | Internal carotid artery | | Dissection | | Aneurysm | | Trauma | | Arteritis | | Thrombosis | | Tumor | | Skull base lesions | | Nasopharyngeal carcinoma, lymphoma | | Cavernous sinus lesion | | Tumors | | Invasive pituitary tumor | | Inflammation | | Thrombosis | | Carotid aneurysm | | Miscellaneous (cluster headache) | |
