An aneurysm is a permanent pathological dilation, a sort of bulge similar to a ball, which affects the wall of a blood vessel, usually an artery. The segment of the vasal wall struck by aneurysm is weakened and may expand until it breaks, resulting in copious bleeding.
The most dangerous aneurysms are those that involve the arteries of the brain, where they can cause a stroke, or those of the aorta, which can cause fatal bleeding within a few minutes.
Even if it does not undergo a tragic break, a large aneurysm can prevent correct blood circulation and favor the formation of blood clots or thrombi.
Aneurysms are often caused by a chronic increase in blood pressure, but any trauma or disease that weakens the vessel wall can be responsible for its onset. Some aortic aneurysms are attributable to inherited disorders, such as Marfan syndrome, an alteration that makes connective tissues weaker (due to the mutation of the FBN1 gene for fibrillin 1). Moreover, it is good to remember that, with age, the vessel walls tend to become less elastic and more subject to dilation.
The symptoms associated with an aneurysm are particularly poor and the diagnosis often occurs accidentally. Treatment and prognosis vary with the location and size of the aneurysm. Some people are more susceptible to developing these abnormal dilations; therefore, the best strategy is to identify those at risk to take the necessary preventive measures.
What is an aneurysm?
An aneurysm is a dilation (or extroflexion) of the wall of an artery, a vein or heart, which occurs as a result of a weakening, caused by a trauma or a pathological alteration. Arterial aneurysms manifest themselves as pulsating dilatations of the vessel, usually associated with arteriosclerosis (degenerative etiology) or inflammatory processes (following an infectious or vascular disease). Other forms, which mainly concern the cerebral arteries, are determined by the congenital or hereditary weakness of the arterial wall (for a lesser development of the vessel's average tunic).
The most frequent causes that promote the formation of an aneurysm are atherosclerosis and hypertension, but all the factors that cause a weakening of the blood vessel walls can be responsible.
The main causes of an aneurysm are:
- A congenital weakness of the muscular tissue of the arterial wall:
- Destruction of the elastic or muscular component of the average habit.
- Genetic predisposition:
- Modified collagen production, unable to tolerate pressure or degenerative insults (Marfan syndrome);
- Altered balance between metalloproteases (MMPs) - capable of degrading the components of the extracellular matrix (collagen, elastin, proteoglycans, elastin, laminin etc.) - and their inhibitors (TIMP).
- A trauma suffered by the blood vessel (insertion of prosthesis, thoracic trauma, post-infarct lacerations, etc.);
- Vascular diseases, such as atherosclerosis, vasculitis, syphilis or other infections.
- Family arrangement;
- Atherosclerotic disease;
- Hypercholesterolemia (high levels of cholesterol in the blood);
- Cigarette smoke;
- Male sex;
- Age over 60 years;
- Chronic obstructive pulmonary disease;
- Pregnancy (often linked to the formation and rupture of splenic artery aneurysms).
Where do aneurysms occur most frequently?
An aneurysm can develop in every part of the body, but the predominantly affected sites are:
- heart : aorta, the main artery of the heart (aortic aneurysm);
- brain : cerebral arteries (cerebral aneurysm);
- limb arteries: leg, at knee level (popliteal artery aneurysm);
- visceral arteries: intestine (mesenteric artery aneurysm) and spleen (splenic artery aneurysm).
Types of aneurysm
There are many types of aneurysms, but the most common are located more frequently at the level of the large arteries, such as the aorta, or of the brain:
Aortic aneurysm (thoracic aortic aneurysm; abdominal aortic aneurysm)
It involves the large vessel that carries arterial blood, rich in oxygen, from the heart to the peripheral vessels. Aneurysms that develop in the abdominal portion of the aorta (abdominal aortic aneurysms) tend to occur in men older than 60 years. Most aortic aneurysms are caused by atherosclerosis, a condition that can weaken the walls of the blood vessel, causing degeneration and dilation of the affected areas.
It consists of the circumscribed dilatation of an intracranial artery (or vein). These alterations can be caused by a head injury, an inherited (congenital) disease, a malformation of the vessels, or even hypertension or atherosclerosis.
From the anatomo-pathological point of view they are distinguished:
- True aneurysm : characterized by the thinning of the elastic lamina of the middle frock, which constitutes the vessel wall and which may be altered qualitatively or quantitatively. The adventitious frock that constitutes the aneurysm wall is preserved;
- Compound aneurysm : it consists of a true aneurysm, which eventually undergoes rupture of the adventitia.
- False aneurysm : all the blood vessel coats are broken and the aneurysm wall is formed by the surrounding tissue.
Depending on the form, aneurysms are distinguished into:
- Saccular aneurysms : they involve short sections (5-20 cm), for a part of the circumference; they are often occupied by thrombus;
- Navicular aneurysms : they involve short strokes, all around the circumference;
- Fusiform aneurysms : affect long stretches (even 20 cm), they are produced following a gradual but gradual expansion of the entire circumference of the vessel;
- Cylindrical aneurysms : affect long stretches, along the entire circumference of the blood vessel.
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