Thoracic aortic aneurysm

A thoracic aortic aneurysm (TAA) is the least common form of aortic aneurysm, the other being abdominal aortic aneurysm. This form of aneurysm is located in the thoracic aorta and can affect any segment of it; most frequently, the aortic root and ascending aorta are affected, followed by the descending aorta and the aortic arch. TAA is defined as an increase in diameter by 50% compared to the normal diameter for that segment. Most are asymptomatic, but can rupture or dissect.

Like AAA, TAA is a disease of elderly men, especially smokers.

Etiology

See aortic aneurysm.

Clinical features

Non-ruptured thoracic aortic aneurysm is mostly asymptomatic. They may compress nearby structures and cause chest, back, or flank pain. Compression may also cause hoarseness or lung symptoms. They may be discovered incidentally, during imaging for other conditions.

Aneurysm rupture or impending rupture causes severe pain, hypotension, and shock.

Diagnosis and evaluation

TAAs may be visualised on contrast CT or MRI. Transtorachic (normal) echocardiography can visualise the proximal aorta but not the distal. Transoesophageal echocardiography can visualise the whole aorta. X-rays are rarely used to evaluate a suspected aneurysm, but they may be seen as a convex contour in the mediastinum on chest x-rays taken for other purposes.

Treatment

Conservative treatment involves regular surveillance with ultrasound (1 – 3x a year), normalisation of blood pressure, smoking cessation, blood lipid reduction, and removal of other risk factors. The goal systolic blood pressure should be 105 - 120 mmHg. This is indicated for asymptomatic AAAs which do not fulfill criteria for elective surgery.

The criteria for elective surgical repair of TAA are aortic diameter > 5,5 cm or rapid expansion or elevated aortic size index or aortic area over height ratio. Surgical repair may be achieved with an open or endovascular technique.

Symptomatic and ruptured TAAs are urgent and emergency indications for surgical repair, respectively.

Complications

The risk of aneurysm rupture increases with the size. TAAs between 4-5 cm have <2% yearly risk of rupture or dissection, but TAAs > 6 cm have >7% risk. ‎