notes by dr Claudio Italiano
Aortic aneurysm is the abnormal dilation of a part of the aortic artery, due
to the failure of the vessel wall whose elastic component has been weakened by
degenerative phenomena:
a) atherosclerotic
b) inflammatory
c) traumatic.
The aorta is the largest of the arterial vessels, originates from the heart, and
from its trunk all the remaining arteries of the organism branch off. Its wall
is made up of three claddings arranged concentrically, in a coaxial manner,
called tunics:
a) the innermost, is the intimate tunic, formed by covering cells (endothelial
cells);
b) the most external is the adventitia habit, formed by connective connective
tissue;
c) in the middle there is the medium tunic, formed by elastic fabric membranes
connected to each other by bundles of elastic fibers and smooth muscle fibers.
Because of the physical laws of fluids, the tension that is produced on the wall of an artery at each cardiac output is proportional to the diameter of the vessel as well as to the pressure. Having a large caliber of the aorta, hypertension is particularly deleterious on a vessel wall rendered inelastic and more prone to flattening. In fact, due to the processes mentioned above, the outcome of the spontaneous reparative mechanisms, which try to replace the elastic fibers damaged by fat deposits (atherosclerosis), with the new material that is fibrous, rigid (arteriosclerosis), is added. ) and therefore insufficient to cushion the pressure load.
The other diseases causing aortic aneurysm may be syphilis, much less common than in the past, tuberculosis, bacterial infections, rheumatoid arthritis. Finally, congenital aneurysms associated with diseases of the heart valves exist.
Arteriosclerosis aortic
aneurysms are produced predominantly in the abdominal tract downstream of the
renal arteries, aneurysm that is discovered, by chance, usually following an
ultrasound examination or an abnormal abdominal pulse.
Abdominal aneurysm is generally asymptomatic and its diagnosis occurs
accidentally during an ultrasound examination performed for other reasons, it
becomes symptomatic when its dimensions are such as to cause pain that occurs
when the same dimensions are such as to compress the surrounding tissues.
Frequent is the formation of thrombus which in turn may cause peripheral arterial emboli. In some cases the aneurysm can be complicated by allowing the passage of blood into the wall and causing pain that may be indicative of imminent rupture of the aneurysm itself. Very often, however, the rupture of the aneurysm occurs in the absence of painful symptoms. In acute aneurysm on an atherosclerotic basis, the patient may have the sensation of pulsation in the abdomen, or back pain. Aneurysm rupture requires urgent surgery.
It's a lesion that occurs more frequently in men than in women, are typically fusiform and extend up to the aortic arch. As a consequence, aortic arch aneurysms are often in continuity with ascending aortic aneurysms. Ascending aortic aneurysms can be divided into three categories based on the mode of aortic root involvement, which has direct implications on surgical treatment.
The most common type is the supracoronarial aneurysm, in which the
area below, that is between the aortic annulus and the coronary ostium, is of
normal size. Aneurysms of this type are very well corrected with prosthetic
tubes positioned above the coronary hosts until the end of the aneurysm. The
second type is defined as ectasia annuloaortica, a term that focuses on the
dilation of both the aortic annulus and the proximal portion of the aorta. This
aneurysm is typical of Marfan syndrome and other related diseases characterized
by cystic medionecrosis of the aortic wall. Since the annulus and the proximal
aorta are the most dilated portions, the ascending aorta takes on a "flask"
shape and the whole aortic bulb and the valve must be replaced, usually with a
prefabricated prosthesis that includes the prosthetic valve and an aortic
prosthetic tube in a single unit. The third category, the tubular type of
ascending aortic aneurysms, presents some aspects in common with the other two
types described. In patients with aneurysms of this type, the annulus and the
proximal aorta are modestly dilated and the caliber of the ascending aorta is
more uniform. When aortic repair is necessary, both a supracononary tube and the
replacement of the entire root may be indicated depending on the patient's age.
In younger individuals a compound valved tube protects better from delayed
dilatation of the proximal portion of the aortic bulb.
The elastic structure of the medium tunic allows the aorta to amortize the
pressure wave that is impressed on the arterial trunk at each heartbeat.
Aneurysm is formed when the fibers of the medium tunic disintegrate, degenerate
or thin, and the repair mechanisms replace them with fibrous tissue which, being
inelastic, tends to be reduced under pressure.
The aorta may be affected by various pathological processes leading to aneurysm,
dissection or ischemic syndromes.
The term aneurysm - derived from the Greek aneurysm, which indicates dilatation - differs from ectasia, a term used to mean a generalized dilatation and a lengthening of the aorta that occur with aging. The criterion for defining small-sized aneurysms is controversial. Although the physiological dimensions of the aorta vary with sex and the body surface, it is generally agreed that the maximum diameter of the thoracic aorta should not exceed 4 cm.
For the abdominal aorta, which usually has smaller diameters of the thoracic segment, it has been suggested that the term aneurysm is limited to situations in which the diameter exceeds 3 cm. Another proposed definition depends on the involved segments that have a diameter from 1.5 to 2 times greater than the norm. Aneurysms can be classified according to morphology, location or etiology. In true aneurysms the aneurysm wall is formed by the normal histological components of the aorta. A false aneurysm instead represents an incomplete break and the wall is not made up of the normal histological components of the aorta. It consists of a fibrous lining, formed by a small perforation of the aorta, initially limited by the adhesion of the surrounding tissues, and which gradually widens over time. The general morphological classification distinguishes true aneurysms as fusiform (the most common) or sacciforms. A fusiform aneurysm is roughly cylindrical and affects the entire circumference of the aorta; a saccular aneurysm is a ball dilation of an area of the aortic circumference. Often a small siding ensures continuity between the aortic lumen and the saccular aneurysm.
It caracterized by the detachment of the aortic wall laminae (within
the medium) which allows longitudinal enlargement of a space filled by the blood
within the aortic wall. Aortic dissection is the most common cause of death due
to human aortic diseases. Atherosclerosis of the aorta may restrict the hosts of
large vessels or produce mobile intraortic masses that can cause emboli to the
central nervous system or other organs. It is necessary to distinguish between
various other conditions. The acute aortic cross section is the consequence of a
trauma and concerns the lesions of an intrinsically normal aortic wall and
resistant to the propagation of the dissection.
The rupture of aortic aneurysm is a process that occurs autonomously, unless you
first encounter an acute aortic section or an acute aortic dissection, which
represent common evolutions.
Acute aortic dissection refers to the separation of the aortic wall laminae, discussed in depth later. An intramural aortic hematoma is similar to a circumferential rather than a longitudinal dissection and there are no identifiable flaps that separate the true lumen from the false lumen. Perforating aortic ulcer refers to a localized perforation of the average lamina of the aortic wall in the context of an atherosclerotic plaque. Aortic aneurysms can also be classified, in relation to the involved segment, in thoracic, thoracoabdominal or abdominal. The aneurysmal formations can concern the entire length of the aorta, while atherosclerotic disease tends to involve only the abdominal portion and the iliac arteries.
The dilatation of the aorta can occur as a consequence of atherosclerosis alone or due to aging, infections, inflammations, trauma, congenital anomalies and degenerations of the average or in conjunction with pathological states. The pathological changes that accompany these conditions may result in thickening, thinning, obstruction, rupture or dissection of the aorta or its alteration caused by a combination of all these factors. The normal aging process favors the onset of degenerative changes affecting the larger bread of the aorta length, leading to mild forms of the condition called cystic medionecrosis. Although essentially a normal aging process, cystic medionecrosis develops more rapidly in patients with a bicuspid aortic valve, during pregnancy and particularly in Marfan syndrome. The mechanism by which the medial layer of the aorta is subject to this accelerated rate of degeneration is the subject of genetic and molecular research. Severe degeneration of the elastic fibers, muscle cell necrosis and interstitial clusters are often found in the ascending aorta, from the valve region to the brachiocephalic artery. Aortic regurgitation may be a secondary feature of aortic root dilatation, although the flaps of the valve are histologically normal. Cystic medionecrosis is the most common cause of ascending aortic aneurysm and, although this type of aortic pathology is typical of Marfan syndrome patients, it can also be observed in subjects with no clinical signs of this syndrome.