ABSTRACT
The thoracic aorta consists of an ascending segment, the arch, and a descending segment. The aortic root is the most proximal portion of the aorta, which is formed by the aortic valve, the annulus, and the aortic sinuses where the aorta has the largest diameter. The coronary arteries arise from the left and right sinuses of Valsalva. The ascending aorta is about 5 cm in length. The aortic diameter becomes mildly larger at the junction of the ascending aorta with the arch (bulb of the aorta). The proximal part of the aortic arch gives rise to the innominate artery, the left carotid, and the left subclavian artery. The most frequent variations of the origin of the great vessels are the common origin of the innominate and left carotid artery, and the separate origin of the left vertebral artery between the left carotid and left subclavian artery. The innominate artery divides in the uppermost portion of the mediastinum; the visualization of four vessels immediately cranial to the arch is frequently associated with an aortic arch anomaly. The junction of the arch with the descending aorta is called aortic isthmus. It extends from the left subclavian artery to the ligamentum arteriosus and is slightly narrower than the proximal and distal segments. The descending aorta is mildly dilated immediately after the ligamentum arteriosus (aortic spindle). The major branches of the descending thoracic aorta are the intercostal and bronchial arteries. The abdominal aorta gives rise to the celiac axis, the
superior and inferior mesenteric arteries, and the renal arteries. At the iliac bifurcation, it divides into the common iliac arteries.
