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Familial aortic dissection
Familial aortic dissection or FAD refers to the splitting of the wall of the aorta in either the arch, ascending or descending portions. FAD is thought to be passed down as an autosomal dominant disease and once inherited will result in dissection of the aorta, and dissecting aneurysm of the aorta, or rarely aortic or arterial dilation at a young age. Dissection refers to the actual tearing open of the aorta. However, the exact gene(s) involved has not yet been identified. It can occur in the absence of clinical features of Marfan syndrome and of systemic hypertension. Over time this weakness, along with systolic pressure, results in a tear in the aortic intima layer thus allowing blood to enter between the layers of tissue and cause further tearing. Eventually complete rupture of the aorta occurs and the pleural cavity fills with blood. Warning signs include chest pain, ischemia, and hemorrhaging in the chest cavity. This condition, unless found and treated early, usually results in death. Immediate surgery is the best prognosis in most cases.〔 FAD is not to be confused with PAU (penetrating atherosclerotic ulcers) and IMH (intramural hematoma), both of which present in ways similar to that of familial aortic dissection.
==Physiology==
FAD is normally associated with Marfan syndrome, Ehlers-Danlo syndrome, and various other genetic disorders which affect the connective tissues of the cardiovascular system. There are various mechanisms by which the medial layers of the lumen are stressed and eventually torn. Once torn these areas begin to fill with blood and become susceptible to aneurysm formation. Depending on the location of the tear, FAD normally affects the ascending or descending aorta, where the primary characteristic of a bulge can be seen. This bulge is the result of the creation of a false lumen due to the vast amount of blood seepage from the aortas and surrounding veins. In some cases it is not uncommon to see degeneration in the ascending and descending aorta and the atrioventricular and semilunar valves due to elastolysis or breakdown and loss of elastic fibers. These connective tissue malfunctions are traceable to mutations, and lack of genes encoding for important components such as collagens, and micro- fibril associated glycoproteins. Breakdown among these connective layers eventually compromises the integrity of the aortic lumen.〔
Depending on the extent of pooling and damage to the blood vessel, the Svensson system was created to diagnose and describe the five classes of pathological processes that may be visible due to the dissection. Class 1 refers to any dissection with a true and false lumen. Class 2 specifically depends on the presence of hematoma or hemorrhaging at the site of the dissection. Class 3 is a dissection without hematoma. Class 4 is recognized by the presence of an ulcer among the lumen. Class 5 has to do with any sort of traumatic hemorrhaging in the dissection. Class 5, in the most case, is the most severe and life threatening due to large amounts of rapid blood loss.
Those experiencing aortic dissection typically will complain of agonizing pains described with a ripping feeling in the chest that for some may migrate to their backs.〔 Anything that compromises or obstructs the amount of blood flow and the delivery of nutrients and oxygen to the walls of the ascending and descending aorta has a large impact on the viability of the layers of the surrounding lumen. Chronic hypertension, Inflammatory disease, excessive plaque build up among coronary walls, intimal thickening, and Arteriosclerosis are all believed to increase the likely hood of FAD occurring in an individual.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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