An aneurysm is an abnormal bulge or ballooning in the wall of a blood vessel. The three main types are aortic aneurysms, which occur in the aorta, cerebral aneurysms located in the brain arteries, and peripheral aneurysms in other arteries. Aneurysms are caused by a weakening of the arterial wall and can manifest as pain, shortness of breath, or nausea depending on their location. Diagnosis involves imaging tests like ultrasound, CT scan, or angiography. Treatment may involve medication, open surgery to replace the damaged vessel section, or endovascular repair using catheters and stent grafts.