What anatomy is involved in a thoracic aortic aneurysm (TAA)?

Updated: Apr 02, 2021
  • Author: Elaine Tseng, MD; Chief Editor: Mary C Mancini, MD, PhD, MMM  more...
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Aneurysms are either true or false. The wall of a true aneurysm involves all three layers, and the aneurysm is contained inside the endothelium. The wall of a false or pseudoaneurysm only involves the outer layer and is contained by the adventitia. An aortic dissection is formed by an intimal tear and is contained by the media; hence, it has a true lumen and a false lumen.

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 according to the Crawford classification, as follows:

  • 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.

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