G Thoracic aortic aneurysm
The mortality rate associated with thoracic aneurysms is well established. Patients with aortic dissections have only a 3-month survival time if they do not undergo surgical repair because the incidence of rupture is high. The refinement of synthetic grafts, surgical and perfusion techniques, and intraoperative management has contributed to improved surgical outcomes. Today the early mortality rate is thought to be less than 10%, demonstrating that elective surgical intervention is an acceptable means of treating thoracic aortic aneurysms.
Aneurysms of the thoracic aorta may be classified with respect to type, shape, and location. Typically, aneurysms involving all three layers of the arterial wall, tunica adventitia, tunica media, and tunica intima are considered to be true aneurysms. In comparison, aneurysms that solely involve the adventitia are termed false aneurysms. The shape of the lesion can also serve as a means of characterizing aneurysms. Fusiform aneurysms have a spindle shape and result in dilation of the aorta. Saccular aneurysms are spherical dilations and are generally limited to only one segment of the vessel wall. Aortic dissection is the result of a spontaneous tear within the intima that permits the flow of blood through a false passage along the longitudinal axis of the aorta. Aneurysms can also be classified according to their location within the aortic arch. In addition, thoracoabdominal aneurysms can be classified into four types on the basis of their location.
Atherosclerosis is the most common cause of aneurysmal pathology. Atherosclerotic lesions occur most often in the descending and distal thoracic aorta and are most often classified as fusiform. Less common causes include the histologic contributions of cystic medial necrosis observed in patients with Marfan’s syndrome, infective and inflammatory processes within the vessel wall, and Takayasu’s arteritis. A genetic predisposition is thought to contribute to the development of aortic aneurysms.
The symptomatology of thoracic aneurysms is often related to the site of the lesion and its compression on adjacent structures. Pain, stridor, and cough may result from compression of thoracic structures. Symptoms related to aortic insufficiency may be observed in aneurysms of the ascending aorta. An upper mediastinal mass may be an incidental finding on conventional chest radiography in an asymptomatic patient. Further investigation with noninvasive methods (e.g., CT and MRI) can show the configuration and location of the aneurysm. Invasive aortography, although associated with a higher risk of complications, provides the most information because it allows evaluation of the coronary vessels and branches of the aortic arch.
Early detection and surgical intervention have made significant contributions to long-term survival. The surgical approach and mode of resection vary according to the location of the lesion within the thoracic aorta. Resection of the ascending aorta and graft replacement necessitate the use of CPB. The aortic valve may also require replacement. Surgical resection of lesions in the transverse arch compromises cerebral perfusion, although various bypass techniques combined with profound hypothermia and circulatory arrest have been used. Aneurysms of the descending aorta may be resected by application of an aortic cross-clamp. However, perfusion to distal organs can be compromised during this procedure. Endovascular thoracic aortic repair is also an option.
Aortic dissection
1. Aortic dissection is characterized by a spontaneous tear of the vessel wall intima, which permits the passage of blood along a false lumen. Although the cause of the dissection is unclear, lesions that were thought to be related to cystic necrotic processes may actually be caused by variations in wall integrity.
2. Hypertension is the most common factor that contributes to the progression of the lesion. Manipulation of the ascending aorta during cardiac surgery may be associated with aortic dissection.
3. The symptoms of aortic dissection are the result of the interruption of blood supply to vital organs. The most serious complication is aneurysm rupture.
4. Diagnosis can be accomplished by the previously mentioned noninvasive techniques; however, aortography appears to be most reliable.
5. Treatment of dissecting aortic lesions depends on their location within the thoracic aorta. Type A lesions have the highest incidence of rupture and require immediate surgical intervention. Type B lesions may initially be managed medically, with the administration of arterial dilating and β-adrenergic blocking agents. Surgical intervention contributes to an improved long-term survival rate. Studies have shown a survival rate of 94% to 95% for repair of dissecting aortic aneurysm by investigators using the newer techniques.
