Laboratory Studies
Laboratry studies to be consiered in this setting include the following:
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Complete blood count (CBC)
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Electrolyte evaluation and blood urea nitrogen (BUN)/creatinine value - Determining renal function is important for stratifying morbidity.
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Prothrombin time (PT), international normalized ratio (INR), and activated partial thromboplastin time (aPTT)
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Blood type and crossmatch
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Liver function tests (LFTs) and amylase lactate values - These tests are indicated for patients with acute dissection or risk of distal embolization
Imaging Studies
Chest radiography
In the case of ascending aortic aneurysms, chest x-rays may reveal a widened mediastinum (see the image below), 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 (TTE) 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 (TEE).
TEE 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. TEE 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 (AAAs) may be visualized by means of ultrasonography (US), but these images do not help define the extent of thoracoabdominal aortic aneurysms (TAAAs).
Carotid US may be needed for patients with carotid bruits, peripheral vascular disease, a history of transient ischemic attacks (TIAs), or cerebrovascular accidents (CVAs) to evaluate for carotid disease.
Intraoperative intravascular US (IVUS) can also be used to provide additional anatomic information and guidance during placement of endovascular stents.
Intraoperative epiaortic US can be performed to scan the aorta for atherosclerotic disease or thrombus.
For more information, see Bedside Ultrasonography, Abdominal Aortic Aneurysm.
Aortography
Aortography (see the image below) can delineate the aortic lumen, and it 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.
Ascending aortogram showing ascending aortic aneurysm. Patient also underwent computed tomography (CT).
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
Computed tomography (CT) with contrast has become the most widely used diagnostic tool in this setting. Contrast CT scans rapidly and precisely evaluate the thoracic and abdominal aorta to determine the location and extent of the aneurysm and the relation 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. (See the image below.)
Computed tomography (CT) scan depicting descending thoracic aortic aneurysm with mural thrombus at level of left atrium.
Sagittal, coronary, and axial images may be obtained with three-dimensional (3D) 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 common femoral artery access is essential to determine the feasibility of large-bore sheath access. Spiral CT with 1-mm cuts and 3D 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 (TAAs). 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. [40]
CT angiography (CTA) may create multiplanar reconstructions and cines. This requires nephrotoxic contrast and radiation, but the procedure is noninvasive.
Magnetic resonance imaging
Compared with contrast CT, magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA) have the advantage of avoiding nephrotoxic contrast and ionizing radiation.
MRI and MRA can also help accurately demonstrate the location, extent, and size of the aneurysm and its relation 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 is.
Other Tests
Baseline electrocardiography (ECG) should be performed. TTE noninvasively screens for valvular abnormalities and cardiac function.
Patients with a smoking history and chronic obstructive pulmonary disease (COPD) should be evaluated by using pulmonary function tests with spirometry and room-air arterial blood gas determinations.
Patients with a history of coronary artery disease or those older than 40 years should undergo cardiac catheterization.
Histologic Findings
Histologic findings may include elastic fiber fragmentation, loss of elastic fibers, loss of smooth-muscle cells, cystic medial necrosis, intraluminal thrombus, and atherosclerotic plaque and ulceration.
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Chest radiograph showing widening of superior mediastinum.
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Computed tomography (CT) scan depicting descending thoracic aortic aneurysm with mural thrombus at level of left atrium.
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Ascending aortogram showing ascending aortic aneurysm. Patient also underwent computed tomography (CT).
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Endovascular repair of thoracoabdominal aortic aneurysm (TAAA). Procedure performed by Inkyong Kim, MD, and Rajeev Dayal, MD, ColumbiaDoctors, New York, NY. Video courtesy of ColumbiaDoctors (https://www.columbiadoctors.org).
