Diseases of the aorta

Editor-in-Chief: Amjad AlMahameed, MD, MPH, RPVI, FACP. Beth Israel Decaoness Medical Center and Harvard Medical School. Boston, USA

Aortic Aneurysm
The term aneurysm is derived from the Greek word (aneurysmos) meaning dilatation. The most common site for true arterial aneurysms is the infra-renal aorta. A true aneurysm is a circumscribed dilatation of the three layers of vessel wall with a diameter increase of at least 50% compared to that of the proximal segment (i.e., the the dilated segment is 1.5 times that of the adjacent proximal segment). Ectasia, on the other hand, is a mild dilatation (luminal diameter increased by <50%) that is due to age-related degenerative changes in the vessel wall. Pheotypically, aneurysms are further classified as fusiform (symmetric involvement of the entire aortic circumference) or saccular (focal outpouching of part of the vessel wall). While most aneurysms are silent, a variety of symptoms and life-threatening complications can occur. Timely diagnosis and treatment of aortic aneurysms is critical.

Thoracic Aortic Aneurysms
Thoracic aortic aneurysms (TAAs) encompass all aneurysms the aorta between the aortic root and the crura of the diaphragm. The aortic root and the ascending vthoracic aorta are the most common sites of TAAs (60%), followed by the descending thoracic aorta (40%). Involvement of the aortic arch and/or extension of a TAA into the abdominal aorta (AA) (so called thoracoabdominal aneurysms) are relatively uncommon subsets (each encountered in 10% of cases or less).

TAAs are relatively uncommon with an estimated incidence between 6 and 10 new aneurysms per 100,000 person-years. TAAs are usually diagnosed after the sixth decade of life and they typically expand slowly (approximately 0.1-0.2 cm/year). The risk of rupture is closely related to aneurysm size (3% for TAAs <4 cm and 7% for >6 cm). These bioepidemiological characteristics support the current stand that screening for TAA is not recommended in the general population. Certain population substrates, such as those with history of Marfan syndrome, Turner syndrome, Ehlers-Danlos type IV syndrome, familial thoracic aortic disease syndromes, and patients with bicuspid aortic valve should have imaging study to screen for TAAs.

Abdominal Aortic Aneurysm
Since the abdominal aorta tends to be about 2 cm in diameter, a true AAA measures >3.0 cm. However, studies showed that the normal diameter varies depending on the patient’s age, sex, height, weight, race, body surface area, and baseline blood pressure. Hence, using a diameter ratio (> 1.5 the proximal segment) may be more accurate, particularly in smaller people such as women and those of short stature.