Subclavian steal syndrome (SSS), also called subclavian steal steno-occlusive disease, is a constellation of signs and symptoms that arise from retrograde (reversed) blood flow in the vertebral artery or the internal thoracic artery, due to a proximal stenosis (narrowing) and/or occlusion of the subclavian artery. This flow reversal is called the subclavian steal or subclavian steal phenomenon, regardless of signs/symptoms being present. The arm may be supplied by blood flowing in a retrograde direction down the vertebral artery at the expense of the vertebrobasilar circulation. It is more severe than typical vertebrobasilar insufficiency. Signs and symptoms Presyncope (sensation that one is about to faint) Syncope (fainting) Neurologic deficits Blood pressure differential between the arms severe memory problems hands showing circulation problems (hands can have blotchy patches of red and white) (associated with other stigmata of vascular disease (e.g. vascular insufficiency ulcers of the fingers). Causes There are multiple processes that can cause obstruction of the subclavian artery before the vertebral artery, giving opportunity for SSS. Atherosclerosis is the most common cause of SSS; all atherosclerotic risk factors are risk factors for SSS. Thoracic outlet syndrome (TOS) increases the risk for SSS. TOS doesn't directly cause SSS, because the site of subclavian artery compression is over the first rib, which is distal to the vertebral artery. TOS has been reported to cause stroke through theorized clot propagation towards the vertebral artery; a similar mechanism could explain how TOS causes SSS. Presence of a cervical rib is a risk factor for both TOS and SSS. Takayasu's arteritis is a disease causing inflammation of arteries, including the subclavian artery. Inflammation leaves behind dense scar tissue, which can become stenotic and restrict blood flow. SSS can be iatrogenic, meaning a complication or side effect of medical treatment, one example being the obstructive fibrosis or thrombosis resulting from repair of aortic coarctation. Another example is Blalock–Taussig anastomosis for treatment of tetralogy of Fallot. The procedure involves dividing the subclavian artery and reconnecting the proximal portion to the pulmonary arteries, leaving the vertebral artery as the primary supply to the distal subclavian artery. Various congenital vascular malformations cause SSS, examples including aortic coarctation and interrupted aortic arch. Pathophysiology Classically, SSS is a consequence of a redundancy in the circulation of the brain and the flow of blood. SSS results when the short low resistance path (along the subclavian artery) becomes a high resistance path (due to