Are you referring to an aneurysm? Its a bulge that develops in the wall of an artery. Aneurysms are common and most develop in older people, particulary in men and in people who have atherosclerosis (hardening of the arteries, weakens) and high blood pressure.
Blood does not flow normally through aneurysms so there is a risk of clots. High blood pressure puts added pressure to the arteries and smoking damages the arteries making aneurysm more likely and hbp can enlarge the bulge and sometimes rupture.
There are medical guidelines to follow that considers the size, progression and symptoms for the appropriate treatment. Controlling blood pressure, blood thinning medication, watching and periodically monitoring would be the procedure to evaluate progression if any.