Thoracic Aortic Aneurysms

About 80% of thoracic aortic aneurysms are secondary to atherosclerosis associated with hypertension. Tertiary syphilis causes about 14%; these aneurysms are always located in the ascending aorta. Other causes include congenital factors, Marfan's syndrome, and blunt trauma to the chest.

Symptoms, Signs, and Diagnosis

Symptoms and signs are related to the site of the lesion. Aneurysms of the ascending thoracic aorta rarely cause pain until they rupture. Examination may reveal a loud aortic closing sound and an early decrescendo diastolic murmur of aortic regurgitation secondary to dilation of the aortic ring. The murmur, usually heard best in the aortic area, may be accompanied by a louder systolic murmur. Palpating the chest of a thin patient who is leaning forward may reveal a pulse along the right sternal border.

Although asymptomatic when small, aneurysms of the transverse thoracic aorta may cause symptoms and signs of mediastinal compression (hoarseness secondary to compression of the recurrent laryngeal nerve, dysphagia, wheezing, and superior vena cava syndrome) as they enlarge. On chest x-rays, these aneurysms may resemble mass lesions and so can easily be confused with bronchogenic carcinomas and mediastinal neoplasms.

Aneurysms of the descending thoracic aorta are generally asymptomatic until very large and can even penetrate the spine without causing pain.

Diagnosis is usually made coincidentally during review of routine chest x-rays. Generally, good posteroanterior and lateral views can distinguish the aorta from other mediastinal structures, and CT can confirm the diagnosis. If an aneurysm seems likely on chest x-ray, contrast CT is recommended to verify its size and location and to distinguish it from a silent aortic dissection. Angiography should be performed only if surgical repair is being considered.

Treatment

Asymptomatic thoracic aortic aneurysms < 8 cm that are not expanding call for a conservative approach. Hypertension should be treated with drugs that do not increase cardiac stroke volume (because the increased volume can stress the aortic wall). -Blockers (nonvasodilator type) and calcium channel blockers are the drugs of choice; methyldopa, clonidine, and diuretics can also be used. Vasodilators (eg, hydralazine, prazosin, angiotensin-converting enzyme inhibitors) should be avoided.

The decision to perform surgery is based on the aneurysm's size and location, the presence of symptoms, and the patient's general condition. Aneurysms < 5 cm in transverse diameter rarely rupture, but those > 10 cm often do. Pain or compression symptoms suggest an increased likelihood of rupture.

Aneurysmal repair is a high-risk procedure for elderly patients, particularly if they have significant cardiopulmonary disease. Surgery should not be considered for most elderly patients. Rather, they should have chest x-rays every 4 to 6 months.

The transverse thoracic aorta is the most difficult site for surgery because total cardiopulmonary bypass and reanastomosis of the extracranial arteries into the graft are required. Surgery on the descending thoracic aorta is less complicated because only partial cardiopulmonary bypass is required to protect the kidneys and spinal cord. Surgery on the ascending thoracic aorta is of intermediate risk. The risk of surgery on the ascending aorta has been reduced by the sleeve technique, in which a vascular graft is inserted inside the aorta without resection of the vessel. For patients with severe aortic regurgitation, a graft with an attached aortic valve can be inserted.