Definition of Thoracic Aortic Aneurysm
A thoracic aortic aneurysm (TAA) is defined as a localized permanent dilation of the thoracic aorta with an increase of at least 50 percent in diameter compared to the normal expected diameter for that aortic segment. The normal diameters for the thoracic aorta are indicated in the text above. Thoracic aortic aneurysms are classified based on the affected aortic segment.
Symptoms
Patients with thoracic aneurysms are often asymptomatic at the time of presentation. When present, symptoms are usually due to compression of adjacent structures, which can lead to chest, back, flank, or abdominal pain.
Depending on the location of the aneurysm, pulmonary symptoms or signs of nerve compression (e.g., hoarseness, diaphragm paralysis) may also occur. Other symptoms may be due to aortic regurgitation or thromboembolism affecting virtually any vascular bed (e.g., coronary, cerebral, renal, mesenteric, lower extremity, and, rarely, spinal cord).
The most serious complications of thoracic aortic aneurysm are aortic dissection and rupture, which most often occur in the left intrapleural space or the intrapericardial space. Rupture is associated with severe pain and hypotension or shock.
Diagnosis
The definitive diagnosis of TAA relies on advanced aortic imaging to confirm the presence of the aneurysm and characterize the diameter and extent.
- Incidental Thoracic Aortic Aneurysms (TAA): TAA is often detected as an incidental finding during chest X-ray, echocardiography, and computed tomography (CT). TAA produces widening of the mediastinal silhouette, enlargement of the aortic knob, or displacement of the trachea from the midline. Simple chest X-ray cannot distinguish a TAA from a tortuous aorta, and therefore, when a TAA is suspected based on radiographic findings, advanced imaging (CT, echocardiography) is necessary to confirm the diagnosis.
- High-risk patients: Most patients with genetic mutations (e.g., Marfan syndrome, Loeys-Dietz syndrome, Turner syndrome) that may predispose to aneurysm/aortic dissection should undergo comprehensive aortic imaging (thoracic and abdominal aorta) at the time of their medical diagnosis.
- Symptomatic patients: Chest X-ray may be useful in the initial evaluation of patients with chest pain or other thoracic symptoms. When suspicion of TAA/dissection is high, a negative X-ray should not delay definitive aortic imaging.
Radiological Imaging
The choice of imaging technique depends on the clinical situation. CT is used more frequently, especially in acute symptomatic patients, to detect TAA, determine its size, define the anatomy of the aorta and branch vessels, and rule out associated aortic dissection. Evaluation of the aortic sinuses may be suboptimal with cross-sectional imaging.
Thus, it is reasonable to perform transthoracic echocardiography (TTE) or transesophageal echocardiography (TEE) to further evaluate the aortic valve or other abnormalities or diseases that might alter management. Transesophageal echocardiography (TEE) is preferred over TTE for examination of the entire aorta, especially in emergencies and for imaging when a concomitant dissection is suspected.
Source: UpToDate