Commonly, a thoracic aortic aneurysm results from atherosclerosis, which weakens the aortic wall and gradually distends the lumen. An intimal tear in the ascending aorta initiates a dissecting aneurysm in about 60% of patients.

Aneurysm of the ascending part of the aorta is usually seen in hypertensive men who are younger than age 60. Aneurysm of the descending part of the aorta, usually found just below the origin of the subclavian artery, is most common in elderly hypertensive men. It’s also seen in younger patients with a history of traumatic chest injury, although less often in those with infection. Aneurysm of the transverse part of the aorta is the least common.

Other causes include:

Pain most commonly accompanies a thoracic aortic aneurysm. (See Clinical characteristics of thoracic dissection.) With an aneurysm of the ascending part of the aorta, the pain is described as severe, boring, and ripping and extends to the neck, shoulders, lower back, and abdomen but rarely radiates to the jaw and arms. Pain is more severe on the right side.

Other signs include bradycardia, aortic insufficiency, pericardial friction rub caused by a hemopericardium, unequal intensities of the right and left carotid pulses and radial pulses, and a difference in blood pressure between the right and left arms. If dissection involves the carotid arteries, an abrupt onset of neurologic deficits may occur.

With an aneurysm of the descending part of the aorta, pain usually starts suddenly between the shoulder blades and may radiate to the chest; it’s described as sharp and tearing.