Arterial aneurysms

Author(s) : Dr Shanan Khairi
Last edited on : 22/09/2024

An arterial aneurysm is defined by a loss of parallelism of the arterial walls (dilation), affecting all layers of the arterial wall, localized, permanent, and generally with a diameter that exceeds by > 50% the size of the normal adjacent segment. Their frequency is increasing and most commonly involves, in order of importance: aorta > iliac > popliteal > femoral >> visceral trunks, renal arteries, and carotids. Their management involves monitoring, controlling risk factors, and in some cases, surgical or endovascular repair.

It is important to distinguish aneurysms from pseudo-aneurysms (or "false aneurysms"), which consist of a blood collection outside the vascular wall due to a loss of vascular integrity, contained by surrounding connective tissue.

Etiologies and Risk Factors

The determining factor seems to be an alteration and/or decrease in the number of elastic fibers (elastin, etc.) in the arterial wall, induced either by congenital connective tissue abnormalities or by inflammatory infiltrates and increased protease activity → thinning and loss of wall resistance. Several risk factors have been identified.

Atheromatosis

It is believed to be the cause of the majority of aneurysms. The main risk factors are smoking (relative risk = 3-5 for abdominal aortic aneurysm), male sex, hypertension, age (typically, the incidence of aneurysms increases with age, peaking in developed countries between 60 and 70 years), dyslipidemia, certain toxins (e.g., cocaine), etc. Association with other conditions (peripheral arterial occlusive disease, cerebrovascular disease, coronary artery disease, etc.) is common.

Familial Forms and Genetic Factors

Several congenital abnormalities and rare connective tissue diseases carry a risk: Marfan syndrome (ascending aortic aneurysm occurs in 80% of cases with a risk of aortic insufficiency, dissection, rupture), Ehlers-Danlos syndrome (particularly type IV), pseudoxanthoma elasticum, cutis laxa, aortic bicuspidy, Turner syndrome, etc. → these abnormalities justify systematic screening (Echo-Doppler) for an aortic aneurysm in the patient and their siblings.

Biochemical Factors and Inflammatory Arteriopathies

The role of inflammation and proteolysis is critical in various etiologies: Horton’s disease, Takayasu’s arteritis, Behçet’s disease, idiopathic inflammation, infectious aneurysms (syphilis, tuberculosis, infectious grafts due to bacteremia [always check for endocarditis] on pre-existing arterial wall abnormalities, etc.).

Mechanical Causes

An aneurysm can develop downstream of a coarctation or stenosis, or following trauma (high-energy trauma, severe sudden decelerations, arterial or aortic valve surgery, endovascular procedures).

Complications

These vary depending on the aneurysm's location. In general, the following can occur:

Dissection and/or aneurysm rupture → the primary cause of mortality.
Thromboembolisms → lower limb ischemia, ischemic strokes, visceral infarcts, etc.
Compression of nearby structures → venous thrombosis, limb edema, urinary disorders, abdominal pain, lower back pain, neuralgia, etc.
Complications specific to the underlying etiology.