動脈瘤I：序論

An aortic aneurysm is a localized dilation or outpouching at a weak point in the artery wall. It can involve different sections of the aorta, including the abdominal aorta, aortic arch, or thoracic aorta. These weakened areas develop due to various etiological factors affecting arterial integrity.

Aortic aneurysms result from congenital anomalies like Marfan syndrome, which weakens connective tissues; infectious causes such as tertiary syphilis and endocarditis; mechanical trauma from blunt or penetrating injuries; and inflammatory conditions like giant cell arteritis. Risk factors include hypertension, coronary artery disease, tobacco use, obesity, and family history.

True aneurysms involve all three arterial wall layers—the intima, media, and adventitia. False aneurysms, or pseudoaneurysms, are bounded only by the outer tunica adventitia or surrounding tissue, with blood leaking through inner layers. Pseudoaneurysms typically result from trauma, infection, or arterial leakage after procedures like intra-aortic balloon pump removal.

True aneurysms are classified as fusiform or saccular. A fusiform aneurysm is a circumferential, spindle-shaped expansion involving the entire circumference of the affected artery. A saccular aneurysm is a pouch-like or bulbous protrusion on one side of the arterial wall, creating an asymmetrical outpouching.

Risk factors for aortic aneurysms include male gender, hypertension, coronary artery disease, family history, tobacco use, high cholesterol, lower extremity peripheral arterial disease, carotid artery disease, previous stroke, and obesity. These factors compromise arterial wall strength and integrity over time.

Congenital disorders like Marfan syndrome are primary connective tissue disorders that weaken the aorta by compromising the integrity and strength of connective tissues. This genetic weakness makes the aorta particularly prone to aneurysms and dissections, increasing the risk of serious vascular complications.

Pseudoaneurysms form when arterial damage during procedures allows blood to leak through inner arterial layers while being contained by the adventitia or surrounding tissue. Common procedural causes include cannula removal during intra-aortic balloon pump use and peripheral artery bypass graft surgery, particularly at graft-to-artery anastomosis sites.