Summary of indications

· Aortic size

· Ascending aortic diameter ≥5.5 cm or twice the diameter of the normal contiguous aorta

· Descending aortic diameter ≥6.5 cm

· Subtract 0.5 cm from the cutoff measurement in the presence of Marfan syndrome, family history of aneurysm or connective tissue disorder, bicuspid aortic valve, aortic stenosis, dissection, patient undergoing another cardiac operation

· Growth rate ≥1 cm/y

· Symptomatic aneurysm

· Traumatic aortic rupture

· Acute type B aortic dissection with associated rupture, leak, distal ischemia

· Pseudoaneurysm

· Large saccular aneurysm

· Mycotic aneurysm

· Aortic coarctation

· Bronchial compression by aneurysm

· Aortobronchial or aortoesophageal fistula

Relevant Anatomy

Ascending aortic aneurysms occur as proximally as the aortic annulus and as distally as the innominate artery. They may compress or erode into the sternum and ribs, causing pain or fistula. They also may compress the superior vena cava or airway. When symptomatic by rupture or dissection, they may involve the pericardium, aortic valve, or coronary arteries. They may rupture into the pericardium, causing tamponade. They may dissect into the aortic valve, causing aortic insufficiency, or into the coronary arteries, causing myocardial infarction.

Aortic arch aneurysms involve the aorta where the innominate artery, left carotid, and left subclavian originate. They may compress the innominate vein or airway. They may stretch the left recurrent laryngeal nerve, causing hoarseness.

Descending thoracic aneurysms originate beyond the left subclavian artery and may extend into the abdomen. Thoracoabdominal aneurysms are stratified based on the Crawford classification. Type I involves the descending thoracic aorta from the left subclavian artery down to the abdominal aorta above the renal arteries. Type II extends from the left subclavian artery to the renal arteries and may continue distally to the aortic bifurcation. Type III begins at the mid-to-distal descending thoracic aorta and involves most of the abdominal aorta as far distal as the aortic bifurcation. Type IV extends from the upper abdominal aorta and all or none of the infrarenal aorta. Descending thoracic aneurysms and thoracoabdominal aneurysms may compress or erode into surrounding structures, including the trachea, bronchus, esophagus, vertebral body, and spinal column.

Contraindications

Aneurysm surgery has no strict contraindications. The relative contraindications are individualized, based on the patient's ability to undergo extensive surgery (ie, the risk-to-benefit ratio). Patients at higher risk for morbidity and mortality include elderly persons and individuals with end-stage renal disease, respiratory insufficiency, cirrhosis, or other comorbid conditions. For descending thoracic aneurysms, endovascular stent grafting is less invasive and is an ideal alternative (with appropriate anatomic considerations) to open repair for patients at high risk for complications of open repair. Stent grafts are also a reasonable alternative (with the appropriate anatomy) to open repair in patients who are not at high risk for complications. Patients must understand that life-long follow-up is required and that long-term durability is unknown.

Proceed to Workup

Laboratory Studies

· CBC count

· Electrolyte evaluation and BUN/creatinine value: Determining renal function is important for stratifying morbidity.

· Prothrombin time, international normalized ratio, and activated partial thromboplastin time

· Blood type and crossmatch

· Liver function tests and amylase lactate values: These tests are indicated for patients with acute dissection or risk of distal embolization.

Imaging Studies

· Chest radiograph

· In the case of ascending aortic aneurysms, chest x-rays may reveal a widened mediastinum, a shadow to the right of the cardiac silhouette, and convexity of the right superior mediastinum. Lateral films demonstrate loss of the retrosternal air space. However, the aneurysms may also be completely obscured by the heart, and the chest x-ray appear normal.

· Plain chest radiographs may show a shadow anteriorly and slightly to the left for arch aneurysms and posteriorly and to the left for descending thoracic aneurysms. Aortic calcification may outline the borders of the aneurysm in the anterior, posterior, and lateral views in both the chest and abdomen.

· Echocardiography

· Transthoracic echocardiography demonstrates the aortic valve and proximal aortic root. It may help detect aortic insufficiency and aneurysms of the sinus of Valsalva, but it is less sensitive and specific than transesophageal echocardiography.

· Transesophageal echocardiography images show the aortic valve, ascending aorta, and descending thoracic aorta, but they are limited in the area of the distal ascending aorta, transverse aortic arch, and upper abdominal aorta. Transesophageal echocardiography can help accurately differentiate aneurysm and dissection, but the images must be obtained and interpreted by skilled personnel.

· Ischemia may be evaluated using dipyridamole-thallium or dobutamine echocardiography scans.

· Ultrasonography

· Infrarenal abdominal aortic aneurysms may be visualized using ultrasonography, but these images do not help define the extent for thoracoabdominal aneurysms.

· Carotid ultrasound may be needed for patients with carotid bruits, peripheral vascular disease, a history of transient ischemic attacks, or cerebrovascular accidents to evaluate for carotid disease.

· Intraoperative intravascular ultrasound (IVUS) can also be used to provide additional anatomical information and guidance during placement of endovascular stents.

· Intraoperative epiaortic ultrasound can be performed to scan the aorta for atherosclerotic disease or thrombus.

· For more information, see Bedside Ultrasonography, Abdominal Aortic Aneurysm.

· Aortography

· Aortography images can delineate the aortic lumen, and they can help define the extent of the aneurysm, any branch vessel involvement, and the stenosis of branch vessels. It describes the takeoff of the coronary ostia.

· For patients older than 40 years or those with a history suggestive of coronary artery disease, aortography helps evaluate coronary anatomy, ventricular function by ventriculography, and aortic insufficiency. It does not help in defining the size of the aneurysm because the outer diameter is not measured, which may miss dissections.

· Disadvantages include the use of nephrotoxic contrast and radiation. The risk of aortography includes embolization from laminated thrombus and carries a 1% stroke risk.

· Computed tomography scan

· CT scans with contrast have become the most widely used diagnostic tool. They rapidly and precisely evaluate the thoracic and abdominal aorta to determine the location and extent of the aneurysm and the relationship of the aneurysm to major branch vessels and surrounding structures. They can help accurately determine the size of the aneurysm and assesses dissection, mural thrombus, intramural hematoma, free rupture, and contained rupture with hematoma.

· Sagittal, coronary, and axial images may be obtained with 3-dimensional reconstruction. Stent graft planning for endovascular descending thoracic aneurysm repairs requires fine-cut images from the neck through the pelvis to the level of the femoral heads. The takeoff of the arch vessels is critical to determine the adequacy of the proximal landing zone, as is assessing the patency of the vertebral arteries, if the left subclavian artery should be covered by the stent graft. Assessment of the common femoral artery access is essential to determine the feasibility of large-bore sheath access. A spiral CT scan with 1-mm cuts and 3-dimensional reconstruction with the ability to make centerline measurements is crucial to stent graft planning.

· Aortic size on imaging is widely used to guide clinical decision making in regards to patients who have thoracic aortic aneurysms. It has been found that the double-oblique plane yields improved agreement with planimetry and differed from the axial plane in proportion to aortic geometric obliquity; therefore, the double-oblique measurement is recommended.^[19]

· CT angiography may create multiplanar reconstructions and cines. This requires nephrotoxic contrast and radiation, but the procedure is noninvasive.

· Magnetic resonance imaging

· MRI and magnetic resonance angiography have the advantage of avoiding nephrotoxic contrast and ionizing radiation compared with CT scans.

· MRI and magnetic resonance angiography can also help accurately demonstrate the location, extent, and size of the aneurysm and its relationship to branch vessels and surrounding organs. These studies also precisely reveal aortic composition. However, they are more time consuming, less readily available, and more expensive than CT scans.

Other Tests

· Electrocardiogram: Baseline ECG should be performed. Transthoracic echocardiograms noninvasively screen for valvular abnormalities and cardiac function.

· Pulmonary function tests: Patients with a smoking history and COPD should be evaluated using pulmonary function tests with spirometry and room-air arterial blood gas determinations.

Date: 2015-12-11; view: 694