Thoracic aortic aneurysm overview

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

A Thoracic aortic aneurysms (TAA) is defined as an expansion or dilation of the aorta greater than 4.5 cm. Thoracic aortic aneurysms (TAAs) encompass all aneurysms the aorta between the aortic root and the crura of the diaphragm. The aortic root and the ascending thoracic aorta are the most common sites of TAAs (60%), followed by the descending thoracic aorta (40%). Involvement of the aortic arch and/or extension of a TAA into the abdominal aorta (AA) (so called thoracoabdominal aneurysms) are relatively uncommon subsets (each encountered in 10% of cases or less).

Causes

Two of the most common causes of thoracic aorta aneurysm are Marfan's syndrome and atherosclerosis. In some centers, a prior history of dissection with aneurysmal dilation is the most common cause of surgical repair.

A complete list of causes in alphabetical order is as follows:

• Ankylosing spondylitis
• Atherosclerosis
• Bacterial infection, often following valvular endocarditis

1. Salmonella
2. Staphylococcus aureus
3. Staphylococcus epidermidis
4. Streptococcus
5. Tuberculosis

• Behcet's disease
• Bicuspid aortic valve with post-stenotic dilation due to turbulence
• Ehlers-Danlos syndrome
• Familial thoracic aortic aneurysms and dissections
• Giant cell arteritis
• Loeys-Dietz syndrome
• Marfan's syndrome
• Previous injury to the aorta such as an aortic dissection
• Syphilis
• Takayasu's arteritis
• Traumatic - Sudden deceleration
• Turner's syndrome

Differentiation of Thoracic Aortic Aneurysm from Other Disorders

Thoracic aortic aneurysms are often asymptomatic and as a result can be easily missed. If chest pain is present, it is critical to differentiate a thoracic aortic aneurysm with dissection from other potential life-threatening diseases which include the following:

• Abdominal aortic aneurysms
• Acute myocardial infarction
• Congestive heart failure
• Aortic regurgitation
• Blunt chest trauma
• Hypertensive emergency
• Hemothorax
• Pneumothorax
• Pericarditis
• Pulmonary embolism
• Cardiac tamponade
• Superior vena cava syndrome

Epidemiology and Demographics

Thoracic aortic aneurysms are relatively uncommon (6 to 10 new ones per 100,000 person years) and are less prevalent than abdominal aortic aneurysm. Thoracic aortic aneurysms are generally diagnosed after the sixth and seventh decades of life. Although men are affected 2 to 4 times as often as women, women are at higher risk of rupture by a factor 6.8.

Risk factors

Hypertension and cigarette smoking are the most important risk factors, though the importance of genetic factors in the development of thoracic aortic aneurysm (such as familial thoracic aortic aneurysm; familial aortic dissection) has been increasingly recognized. Approximately 10% of patients may have other family members who have aortic aneurysms. It is also important to note that individuals with a history of aneurysms in other parts of the body have a higher chance of developing a thoracic aortic aneurysm.

Specific thoracic aortic aneurysm risk factors include:

• Smoking or chewing tobacco
• High blood pressure
• Bicuspid aortic valves
• Atherosclerosis (buildup of plaque in the arteries that can damage the lining)
• Gender

• Aortic aneurysms are three time more prevalent in males versus females

• Race

• Aortic aneurysms are more frequent in Caucasian individuals versus other races

• Individuals who have a family history of aortic aneurysms have a much higher risk of rupture and tend to develop aneurysms at a younger age
• Chronic obstructive pulmonary disease
• Previous repair of a thoracic aorta aneurysm
• Turners syndrome

Natural History, Complications, And Prognosis

Thoracic aortic aneurysms typically expand slowly at a rate of approximately 0.1-0.2 cm/year. Aortic dissection and aortic rupture are the two most feared complications of an aortic aneurysm. The five-year survival of patients with a thoracic aortic aneurysm is 56%. The following are associated with a poorer prognosis: the presence of diastolic dysfunction; trauma as a cause of the aneurysm; the presence of coronary artery disease and the presence of carotid artery disease.

Screening

Screening for TAA is not recommended in the general population. However, certain population substrates, such as those with history of Marfan's syndrome, Turner's syndrome, Ehlers-Danlos type IV syndrome, familial thoracic aortic disease syndromes, bicuspid aortic valve, Takayasu arteritis, giant cell arteritis, Loeys-Dietz syndrome or a confirmed genetic mutation known to predispose to aortic aneurysms and aortic dissections (TGFBR1, TGFBR2, FBN1, ACTA2, or MYH11) should have imaging study to screen for TAAs. First-degree relatives of people with thoracic aortic aneurysm or dissection should have aortic imaging to identify asymptomatic disease. Patients with high risk syndromes such as Marfan's syndrome and Loeys-Dietz syndrome should undergo complete aortic imaging at initial diagnosis and 6 months thereafter to establish if enlargement is occurring.

Surgery

Indications for surgical repair of a thoracic aortic aneurysm include rupture; symptoms such as pain consistent with impending rupture; aortic regurgitation; growth ≥ 0.5 - 1 cm/year; bicuspid aortic valve; asymptomatic patients with degenerative thoracic aneurysm, chronic aortic dissection, intramural hematoma, penetrating atherosclerotic ulcer, mycotic aneurysm, or pseudoaneurysm, who are otherwise suitable candidates and for whom the ascending aorta or aortic sinus diameter is 5.5 cm or greater should be evaluated for surgical repair; patients with Marfan syndrome or other genetically mediated disorders (vascular Ehlers-Danlos syndrome, Turner syndrome, bicuspid aortic valve, or familial thoracic aortic aneurysm and dissection) should undergo elective operation at smaller diameters (4.0 to 5.0 cm depending on the condition; to avoid acute dissection or rupture, adult patients with Loeys-Dietz syndrome should undergo surgery for an aortic diameter of >4.4 to 4.6 cm; if a Marfan syndrome patient is contemplating pregnancy, they should undergo aortic root replacement if the diameter is greater than 4 cm, and patients undergoing aortic valve repair or replacement and who have an ascending aorta or aortic root of greater than 4.5 cm should be considered for concomitant repair of the aortic root or replacement of the ascending aorta. A woven dacron tube graft is most commonly used in the repair of thoracic aortic aneurysms.