I- GENERAL – DEFINITION :
Atherosclerosis is a chronic blood disorder whose etiology remains unknown. The role in the appearance of lesions, hemodynamic factors, Local metabolic and general disorders
(hyperlipemia, diabetes, etc) actually a disease that integrates with both the metabolic and vascular disease.
WHO definition (1957) : Atherosclerosis is a intimal alterations variable association of large and medium arteries consisting of a focal accumulation of lipids, complex carbohydrates, blood and blood products, fibrous tissue and calcium deposits, all accompanied by the media changes.
II- CIRCUMSTANCES OF APPEARANCE :
- Atherosclerosis is a disease whose frequency increases with age, the first lesions appear in young adults, early teens.
- Its progression is insidiously.
- Revelation to a more or less late age (on average after 50 years), clinical manifestations usually being the fact of complications due to partial or complete obstruction of the artery.
III- LOCATION OF DAMAGE :
Atherosclerosis reached so selective elastic arteries (Aorta) and musculo-elastic (large arteries vending). Lesions predominate at the bends, bifurcations, Birth collateral, Arterial segments attached to the backbone, that is to say in the territories or appear disturbances in blood flow
IV- ASPECTS OF PATHOLOGICAL ANATOMY atherosclerotic lesions :
Lesions of the Aorta :
1- INITIAL DAMAGE :
MACROSCOPIE : One can recognize :
- The elevations gelatiniform : small translucent elevations, protruding into the lumen.
- The fatty streaks : narrow strips of a few mm to 1 cm long, elongated in the direction of flow.
- Crosslinked aspects : network formed by transverse and longitudinal fatty streaks.
- The fibrous plaques : areas of intimal thickening greyish.
HISTOLOGY : The first three types of lesions consist of lipid laden cells. These cells are histiocytes, fibroblasts or myoblasts. Their clusters are grouped under the intima. edema lesions in the interstitial tissue of the intima may be associated.
The fibrous plaque is made of a very young edematous sclerosis with alteration of the innermost elastic blades.
EVOLUTION : Only the first two aspects would be likely to disappear gradually ; others progress to permanent damage.
2- THE ATHEROSCLERATE PLATE :
MACROSCOPIE : Two aspects are recognizable :
- The milky plate : lenticular training, less than one cm, projecting into the vessel lumen, smooth surface, sparkly, greyish or yellowish.
- The cartilaginous plate : irregularly rounded training 3-4 cm diameter 1-5 mm, protruding into the lumen, sinks into the media thinned next, pearly white, of hard consistency, cartilagineuse, having to cut a central portion made of crumb slurry, yellowish, surrounded by a fibrous tissue pearly white.
- The milky plate : corresponds to the accumulation in the connective tissue of the intima of acid mucopolysaccharides, sometimes fibrin. Contact with deposits, appear histiocytes, fibroblasts and myofibroblasts from the media. These cells are responsible for lipids and become foam cells.
- The cartilaginous plate : as a result of necrosis and connective tissue lipophages, appears formed cellular debris and especially lipids. In the neighboring connective tissue have histiocytes, giant cells and lipophages. A collagen sclerosis surrounds the necrotic focus. These lesions are in the deep part of the intima and are accompanied by damage to the media ( fragmentation of elastic blades, interstitial fibrosis, disappearance of smooth muscle fibers).
3- INJURY ADVANCED :
Atherosclerosis is an irreversible evolutionary process that inexorably worsens. The plates extend, confluence for sometimes deform an entire aortic wall. One sees calcium deposits realizing calcifications visible on radiographs.
4- COMPLICATIONS :
- The anévrysme
- Parietal thrombosis with risk of embolism.
INJURY ARTERIES VENDING
These are generally the same, some features are worth noting :
- Importance of multiple intimal.
- Evolution towards a gradual reduction in light ( stenosis ) reducing the amount of blood reaching the tissues, with ischemia during exercise ( angina, claudication intermittente ).
- Risk of sudden obliteration by thrombosis or hemorrhage within atherosclerotic plaque, responsible infarction.
V- PHYSIOPATHOLOGICAL MECHANISMS OF L’ATHEROSCLEROSIS :
A – Humoral THEORY OR PLASMA :
Explaining the atheroma by deposits of blood elements in the wall with secondary degenerative phenomena, lipid disturbances being the main cause of atherosclerotic deposit.
B – THEORY OR TISSUE PARIETAL :
Evoking an inflammatory condition or dystrophic initial wall. The early atherosclerotic lesions begins in the arterial intima which plays an important role in filtering the plasma-infusion of the arterial wall.
The main mechanisms are discussed :
1- Edema of the intima and endothelial injury :
- edema secondary to lesions of the endothelium making it permeable. Endothelial lesons be due to factors or hemodynamic (HTA), or biochemical (serotonin, catecholamines).
- Other possible causes : Ruptures of the resilient blades with light touches hypertensive, abnormalities of fibroblast synthesis under the aging effect- diabète.
2- lipid deposits :
spaces increase in size between intercellular endothelial cells allowing the passage of larger molecules that normally and in particular the transition lipoprotein.
3- fibrin deposits :
From the plasma fibrinogen.
4- Endothelial injury and thrombosis parietal :
Any breach inducing endothelial commissioning of platelet adhesion mechanism. Clots formed are then incorporated gradually into the intima and the lysis of erythrocytes and platelets provides lipids in the wall.
5- autoimmune mechanisms :
Role of autoimmunity F.
WE- RISK FACTORS :
1- L’AGE : The frequency of atherosclerosis increases with age.
2- SEX : Women are less affected before menopause, This is due to confer protection as their natural estrogen.
3- THE LIFESTYLE : The socio-economic development and diet play an important role.
4- SMOKING : some role.
5- THE ROLE ground, the genetic constitution, family antecedents is retained.
6- HTA, Obesity, hyperlipemia, Diabetes.
These risk factors, associate most often. They are significant to know to perform prevention of atherosclerosis, only means currently in possession doctors to reduce the frequency of accidents due to atherosclerosis, which currently represents the biggest cause of death prior to cancer in France.
Course of Dr N. lemma – Faculty of Constantine