Dissections aiguës de l'aorte : physiopathologie et diagnostic

Abstract

Acute dissection of the aorta is defined by the sudden irruption of a pressurized blood flow trough a tear into the internal part of the aortic wall, resulting into longitudinal separation of the wall along its weakest constituent, and leading to the formation of two circulating channels. It represents the worst catastrophe affecting the human vascular network. Its spontaneous mortality, when the ascending aorta is involved, reaches 50% at 48 hours, 60% after one week and 90% after one month, due to aortic rupture, intrapericardial tamponnade, malperfusion of vital end organs or massive aortic valve regurgitation. Its prevalence is estimated between 4 and 10 for 100 000, and the male-female ratio is about 80%. Acute aortic dissections occur generally on aortas weakened by either hereditary dystrophic conditions such as Marfan’s syndrome or familial annulo-aortic ectasia, or congenital diseases such as bicuspid aortic valve or coarctation, or acquired diseases mainly related to atheroma. Arterial hypertension, either chronic or more often in the form of sudden thrust, plays a major role in the occurrence of acute dissection. The dissecting process extends more or less along the vessel but generally reaches the bifurcation and the iliac arteries. In most patients, the vascular damages, constituted within a few seconds or minutes, may explain the clinical symptoms, the observed complications and may determine the therapeutic strategy. The clinical patterns observed are highly heterogeneous. The most consistent symptom (present in 90% of the patients) consists in an intense thoracic pain which may be associated in a variable manner with cardiogenic shock, transient or permanent neurological disorders, peripheral ischemia, abdominal pain, etc… Any diagnostic suspicion must be confirmed by chest X ray, and above all by trans-thoracic echocardiography, a simple technique which can be performed easily even in emergency rooms or in non specialized units. In case of probable diagnosis, the patient must be referred to a cardio surgical ICU in order to confirm the acute dissection and to analyse its consequences. Presently, trans-oesophageal echocardiography and computerized tomography (CT scan) are the gold standard in terms of rapidity, safety, sensibility and specificity whereas, because of its invasive nature, aortography has lost its pre-eminence and Magnetic Resonance Imaging, although quite contributory, is difficult to perform on an emergency basis in patients with, generally, haemodynamic instability.