There are multiple processes that can cause obstruction of the<unk>  artery before the vertebral artery, giving opportunity for<unk> . Atherosclerosis is the most common cause of<unk> ; all atherosclerotic risk factors are risk factors for<unk> . Thoracic outlet syndrome (TOS) increases the risk for<unk> . TOS doesn't directly cause<unk> , because the site of<unk>  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<unk> . Presence of a cervical rib is a risk factor for both TOS and<unk> . Takayasu's arteritis is a disease causing inflammation of arteries, including the<unk>  artery. Inflammation leaves behind dense scar tissue, which can become stenotic and restrict blood flow.<unk>  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<unk>  artery and reconnecting the proximal portion to the pulmonary arteries, leaving the vertebral artery as the primary supply to the distal<unk>  artery. Various congenital vascular malformations cause<unk> , examples including aortic coarctation and interrupted aortic arch.
Subclavian steal syndrome
Raynaud syndrome
Popliteal artery entrapment syndrome
Aortic dissection
Superior vena cava syndrome
Iliocostal friction syndrome
Inferior vena cava syndrome
Acute aortic syndrome