22.15: Aneurysm I: Introduction

An aortic aneurysm is a localized outpouching or dilation at a weak point in the artery wall. It may involve different parts of the aorta, such as the abdominal aorta, aortic arch, or thoracic aorta.

Etiological factors

Several disorders are associated with aortic aneurysms.

• Congenital causes, such as primary connective tissue disorders like Marfan syndrome, impact the integrity and strength of connective tissues, notably affecting the aorta. Marfan syndrome is a genetic disorder that specifically weakens the aorta, making it prone to aneurysms and dissections.
• Infectious causes mainly arise from bacterial infections, with tertiary syphilis being a prominent example.
• Mechanical causes, such as penetrating trauma from stab wounds or blunt trauma from car accidents, are less common but can severely damage the aorta.
• Inflammatory causes, such as aortitis, involve aortic wall inflammation and are observed in conditions like giant cell arteritis. Giant cell arteritis is an autoimmune condition that can lead to severe inflammation of the aorta and its branches, potentially causing aneurysms or blockages.

Risk factors

Risk factors for aortic aneurysms may include male gender, hypertension, coronary artery disease (CAD), family history, tobacco use, high cholesterol, lower extremity peripheral artery disease (PAD), carotid artery disease, previous stroke, and obesity.

Classifications

Aneurysms are categorized as true or false aneurysms.

A true aneurysm includes all three layers of the arterial blood vessel wall. True aneurysms are subdivided into fusiform and saccular types. A fusiform aneurysm is a circumferential and spindle-shaped expansion of the entire circumference of the involved vessel. A saccular aneurysm is a pouch-like or bulbous protrusion on one side of the arterial wall.

False aneurysms, or pseudoaneurysms, are abnormal outpouchings or dilatations of arteries that are bounded only by the outer layer or tunica adventitia of the arterial wall. These differ from true aneurysms, bound by all three arterial wall layers: the intima, media, and adventitia. Pseudoaneurysms typically occur when the vessel wall is damaged, allowing blood to escape through the inner layers but remain contained by the outermost layer or surrounding tissue. This containment creates the appearance of an aneurysm, though it lacks the structural integrity of a true aneurysm. False aneurysms may result from trauma, infection, or arterial leakage after removing a cannula, such as those used in intra-aortic balloon pump procedures or after peripheral artery bypass graft surgery, particularly at the site of graft-to-artery anastomosis.