What is an aneurysm?

Controlling risk factors, such as obesity or hypertension, is essential to avoid the appearance of an aneurysm, a dilation of a blood vessel that can cause it to rupture.

An aneurysm is a pathological dilation of a blood vessel segment that usually occurs at the arterial level, especially in the aorta artery.

The aorta artery is the conduit through which the blood expelled by the left ventricle is distributed to the general arterial tree. Four sections are distinguished in the aorta: ascending (initially, next to the heart), aortic arch, descending thoracic, and abdominal. It measures approximately 3 cm in diameter in adults at its origin, 2.5 cm in its descending portion in the thorax, and 2 cm in the abdomen.

When the aortic wall (made up of three layers: internal, middle, and external) weakens, a localized and permanent widening can occur, which is what is known as an aneurysm, and if it reaches a specific diameter (the risk increases from 5 cm) can lead to a rupture of the blood vessel.

What are the risks of an aneurysm?

Thoracic aortic aneurysm

The most important risk is the possibility of a rupture of the aorta, which is related to the size of the aneurysm and the presence of symptoms. It increases considerably in the ascending aorta’s aneurysms more significantly than 6 cm and those of the descending thoracic aorta more critical than 7 cm.

Aneurysm of the abdominal aorta

The risk of rupture increases with the size of the aneurysm. The risk of rupture of aneurysms with a diameter less than 5 cm is 1-2% at 5 years, while those with a diameter greater than 5 cm reach 20-40%. The formation of a mural thrombus (a blood clot that partially obstructs the blood vessel) inside the aneurysm predisposes to peripheral embolism (a condition that results in decreased blood flow and tissue oxygenation).

Causes of aneurysm

The aortic aneurysm is frequently associated with atherosclerosis. Controversy exists as to whether atherosclerosis itself actually causes the aortic aneurysm or whether it develops secondarily in the previously dilated aorta. 75% of atherosclerotic aneurysms are located in the distal abdominal aorta, below the renal arteries.

Another cause of an aneurysm is cystic necrosis of the middle layer (which affects the proximal aorta, next to the heart), consisting of the degeneration of collagen and elastic fibers of the middle layer of the aorta and the formation of cysts that weaken the aortic wall. This disorder is highly prevalent in patients with Marfan and Ehlers-Danlos syndrome. Still, it is also seen in association with pregnancy, hypertension, heart valve disease and sometimes as an isolated process in people without any apparent illness. In 20% of cases, it appears that the condition has a genetic basis.

There are also infections capable of producing aneurysms. For example, syphilis is a cause of aortic aneurysms, although relatively rare.

Tuberculous aneurysms usually involve the thoracic aorta and directly affect the spread of infection from neighboring lymph nodes or abscesses.

A fungal aneurysm is a rare lesion that occurs due to localized infections in the wall of the blood vessels and is caused mainly by bacteria from the staphylococcal, streptococcal, and salmonella family. It usually occurs on previously damaged areas of the aorta, as an atherosclerotic plaque.

Regarding the cause, according to the anatomical location of the aneurysm, cystic necrosis of the middle layer is the most frequent cause of ascending aortic aneurysm, while atherosclerosis is of arch or arch aneurysms (curvature that makes the aorta) and the descending thoracic aorta.