What is a thoracic aortic aneurysm?
An aortic aneurysm is an enlargement of a weakened area of the aorta. Aneurysms which involve the ascending aorta, aortic arch and descending thoracic aorta are termed "thoracic aortic aneurysms." Aneurysms in these regions are prone to rupture once they reach a certain size (see below). Fifty percent of patients who experience a rupture of a thoracic aortic aneurysm die before reaching the hospital. Furthermore, surgical repair of a ruptured thoracic aneurysm carries a 25-50% mortality as opposed to a 5-8% mortality when such aneurysms are treated electively.
Ascending Aortic Aneurysm Descending Thoracic Aneurysm
Descending Thoracic Aneurysm
Abdominal Aortic Aneurysm Thoracoabdominal Aneurysm
Thoracoabdominal Aneurysm
Most thoracic aneurysms are asymptomatic and are typically detected when imaging studies (chest x-rays, CT scans, MRI, etc) are being obtained for unrelated reasons. When aortic aneurysms reach larger sizes the symptoms are typically based on the location of the aneurysm.
Ascending aortic aneurysms frequently cause dilatation and leakage of the aortic valve. This can result in shortness of breath or even heart failure should the leakage be severe. Ascending aortic aneurysms can also result in a dull pain underneath the breastbone or radiating to the upper back.
Aortic arch aneurysms can also produce upper chest and back pain. However, when large, these aneurysms can compress both the esophagus and the airway resulting in difficulty swallowing and hoarseness.
Descending thoracic aneurysms are mostly asymptomatic, but can occasionally cause back pain. In contrast, abdominal and thoracoabdominal aneurysms may cause a pulsating feeling in the upper abdomen. Abdominal and back pain may also be present if the aneurysm increases in size.
Whereas, most of the symptoms of stable thoracic aneurysms are vague and non-specific, rupture or dissection of these aneurysms produces dramatic symptoms. A ripping sensation within the chest accompanied by severe pain in the back between the shoulder blades is the most typical complaint during thoracic aortic dissection or rupture. Dizziness, difficulty walking and speaking can all accompany this acute event. Patients with known aortic aneurysms experiencing such symptoms need to contact their physician or surgeon immediately and go to the nearest emergency room.
What are the causes of Thoracic Aortic Aneurysms?
Idiopathic cystic medial degeneration
The most common cause of ascending aortic aneurysms is a condition known asidiopathic cystic medial degeneration. The elastic fibers which make up the outer wall of the aorta normally break down as we age, making the aorta more prone to dilation. In some patients this process is accelerated resulting in early aneurysm formation. We presently do not know the exact mechanisms involved in this process (hence the term idiopathic). Cystic medial degeneration can also be the cause of aortic arch and descending thoracic aneurysms. It rarely is the causeof thoracoabdominal or abdominal aortic aneurysms.
Atherosclerosis
Atherosclerosis is the term used to describe hardening of the arteries. Smoking, high blood pressure and high cholesterol are the primary causes of atherosclerosis. Atherosclerosis typically results in blockages of arteries that deliver blood to the heart (coronary arteries), the legs (femoral arteries), or the brain (carotid arteries). The damage caused to the aortic wall by atherosclerosis can result in aneurysm formation.
Genetic disorders
Marfan syndrome is a genetic condition which is transmitted from parent to child that affects the connective tissues throughout the body. The defect is in the gene that makes fibrillin, a major elastic fiber protein found in the wall of the aorta. Nearly all patients with Marfan syndrome develop aneurysms of the ascending aorta and subsequent leakage of the aortic valve. These aneurysms are prone to rupture at smaller sizes when compared to aneurysms of other etiologies. The risk of aortic dissection is likewise significantly increased in Marfan syndrome. Patients withMarfan syndrome may also develop leakage of the mitral valve. Connective tissue abnormalities throughout the rest of the body can result in slender, tapering fingers, long arms and legs, curvature of the spine and eye problems.
Certain families without specific genetic disorders may exhibit a strong history of aortic aneurysm formation. If a sibling or parent has been diagnosed with an aortic aneurysm, there may be an increased risk of aortic aneurysm formation in the patient.
Aneurysms Associated with Aortic Dissection
An aortic dissection results when the inner layer of the aorta separates from the middle layer of the aorta (see above). When this occurs within the ascending aorta it is frequently fatal unless emergency surgery is performed. However, in the descending aorta, an aortic dissection can typically be treated with medications. Nonetheless, the dissection weakens the aortic wall and the aorta is then prone to aneurysm formation. Chronic dissections need to be managed like all other aneurysms and surgery is indicated once a certain size is reached.
Aneurysms Associated with Bicuspid Aortic Valve
A bicuspid aortic valve is one which contains 2 leaflets instead of the usual three. Such valves are prone to both leakage and stenosis. A bicuspid aortic valve is composed of abnormal connective tissue. This same abnormal tissue also composes the ascending aorta making it susceptible to aneurysm formation. Patients with bicuspid aortic valves frequently have aneurysms of the ascending aorta and surgery on the aortic valve should involve replacement of the aorta should there be any aortic dilation.
Other Causes
Infection of the aortic wall (bacterial, syphilis, etc.) can rarely result in an aneurysm known as a "mycotic aneurysm." Inflammatory aortic aneurysms are a special type of aneurysm associated with a vigorous fibrotic and inflammatory response and require special surgical interventions. Takayasu's arteritis is an autoimmune inflammatory response which is typically found in Japanese patients and results in aneurysms of the ascending aorta and aortic arch.
How are thoracic aneurysms diagnosed?
Suggestions of a thoracic aneurysm can frequently be inferred from routine chest X-rays. However, thoracic aneurysms are most reliably diagnosed with a CT scan or MRI. Frequently, the diagnosis is made when one of these imaging studies is performed for symptoms unrelated to the aneurysm. Echocardiography is important for the evaluation of the aortic valve and also can be used to evaluate the size of the ascending aorta.
Can anything prevent their growth?
Once an aneurysm is diagnosed, strict control of the blood pressure and avoidance of smoking are two interventions which may prevent growth. At present there are no medications which can either shrink the aneurysm or prevent its growth.
When is surgery indicated?
Once a thoracic aneurysm is diagnosed, routine, scheduled follow-up is necessary by an aortic specialist. Aneurysm size needs to be followed closely and surgery is warranted if there is rapid growth over a short period of time or if a critical size is reached. Follow-up typically includes CT scans or MRI's every 6-12 months.
The ascending aorta grows at a rate of 0.10 cm per year and the descending aorta at a rate of 0.20 cm per year. Should an aneurysm increase in size by 0.4cm in any one year then surgery should be performed.
Aortic size | ||||
Yearly risk | > 3.5cm | >4.0cm | >5.0 cm | > 6.0cm |
Rupture | 0.0% | 0.3% | 1.7% | 3.6% |
Dissection | 2.2% | 1.5% | 2.5% | 3.7% |
Death | 5.9% | 4.6% | 4.8% | 10.8% |
Any of the above | 7.2% | 5.3% | 6.5% | 14.1% |
Given these statistics it is recommended that asymptomatic ascending aortic aneurysms be resected at a size of 5.0-5.5 cm. If severe aortic insufficiency is present in the setting of a bicuspid valve, the ascending aorta should be resected when it is 4.5 cm in diameter. Descending thoracic and aortic arch aneurysms typically are resected when they exceed 6.0 cm in diameter. A patient with Marfan's syndrome typically warrants earlier intervention. Symptomatic aneurysms should be resected regardless of size.
What is the Treatment?
Surgery to repair an ascending aortic or arch aneurysm involves removing theaneurysmal portion of the aorta and replacing it with an artificial Dacron tube. If the aortic valve is damaged it also need to be replaced or repaired. Replacement options include mechanical and tissue valves (see valve surgery link).
This type of surgery traditionally has been performed by dividing the breastbone. At the St. Luke's-Roosevelt Aneurysm Center, minimally invasive surgical techniques are now routinely being applied to ascending and arch aneurysm resection. Instead of dividing the breastbone, the upper part of the sternum is only partially divided. This allows for less blood loss and quicker recovery.
Descending Thoracic Aneurysms
The traditional approach to descending thoracic aneurysms is through an incision made in the side and between the ribs. The diseased portion of the aorta is removed and replaced with a Dacron graft. However, techniques of endovascular abdominal aortic aneurysm repair are now applicable to some descending thoracic aneurysms. In this procedure two small incisions are made in both groins and a graft is placed inside the aneurysm in order to exclude it from the circulation. These devices are presently only available in the United States
Below is the angiogram of a complicated patient treated with endovascular surgery for a descending thoracic aneurysm.
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