Acute aortic syndrome is an acute, potentially fatal pathology within the wall of the aorta, including aortic dissection, intramural hematoma (IMH), and penetrating atherosclerotic ulcer. The incidence of acute aortic syndrome ranges from 3.5 to 6.0 per 100,000 patient-years in the general population, but progressively increases with age (27 per 100,000 patient-years in patients ages 64-74 years, and 35 per 100,000 patient-years in patients ≥75 years). Acute aortic dissection comprises 85-95% of all acute aortic pathologies. This article includes a review of the pathophysiology, presentation, diagnosis, and available therapies for acute aortic dissection and IMH based on a review of 82 published reports on the topic. The following are key points:

1. Pathophysiology. The inciting event in IMH is rupture of the vasa vasorum, causing bleeding into the aortic media; IMH can progress to acute aortic dissection if the intimal layer ruptures, with the creation of an entry tear. The presence of an entry tear is pathognomonic for acute aortic dissection; however, most entry tears (most acute aortic dissections) occur spontaneously, rather than as a result of IMH.
2. Classification. Acute aortic pathologies are classified using either the Stanford or the DeBakey system. Stanford type Al lesions involve the ascending aorta, whereas type B lesions are confined to the descending aorta. The DeBakey system accounts for pathology affecting both the ascending and descending aorta (type I), only the ascending aorta (type II), or only the descending aorta (type III).
3. Acute aortic dissection demographics. The average age of patients presenting with acute aortic dissection ranges from 48-67 years (median 61 years) and 50-81% of patients are men. Hypertension is the most common comorbidity (45-100% of patients), followed by smoking history (20-85% of patients), chronic renal insufficiency (3-79%), chronic obstructive pulmonary disease (5-36%), and stroke or transient ischemic attack (0-20%).
4. Acute aortic dissection symptoms. The most common presenting symptom of aortic dissection is chest or back pain (84.8%), often described as “sharp.” Women with aortic dissection present at older ages than men (49.7% of women were >70 years vs. 28.6% of men); and more often with atypical symptoms, leading to delayed diagnosis and higher mortality (30.1% for women vs. 21.0% for men, p = 0.001). Compared with white patients, black patients with aortic dissection tend to be younger, and have a higher prevalence of cocaine abuse, uncontrolled hypertension, and diabetes; however, in-hospital and 3-year mortality is not different.
5. Acute aortic dissection diagnosis. The initial diagnostic evaluation should include computed tomography (CT) or magnetic resonance imaging (MRI), or potentially transesophageal echocardiography (TEE), with comparable sensitivities and specificities (CT 100% and 100%, respectively, MRI 95-100% and 94-98%, respectively, and TEE 86-100% and 90-100%, respectively). If imaging is not available, elevated D-dimer (reflecting early damage to the aortic wall) has a sensitivity of 51.7-100% (median 93.5%) and specificity of 32.8-89.2% (median 54%) at a threshold of 0.5 μg/ml (convert to nmol/L by multiplying by 5.476).
6. Acute aortic dissection treatment and prognosis. The reported short-term (30-day or in-hospital) mortality for type A acute aortic dissection is 13-17% (median 14%) for open surgical procedure and 0-16% (median 7%) for thoracic endovascular aortic repair (TEVAR). The reported early mortality for type B acute aortic dissection is 0-27% (median 7%) for medical treatment, 13-17% (median 16%) for open surgical procedures, and 0-18% (median 6%) for TEVAR.
7. IMH demographics. IMH typically occurs in patients with severe atherosclerotic disease. Fewer than 10% of events resolve spontaneously, whereas 16-47% progress to dissection. The average age of patients presenting with IMH ranges from 58-71 years (median 68 years), and 50-81% are men.
8. IMH diagnosis. CT and MRI are the gold standards for the diagnosis of IMH; CT identification of intimal defects (discrete erosions of the vessel wall) is associated with progression to acute dissection.
9. IMH treatment and prognosis. The early (in-hospital and 30-day) mortality of patients with IMH is 4-19% (median 8%) for medical management, 11-24% (median 17%) for open surgical repair, and 0-6% (median 2%) for TEVAR. However, these rates are limited by sources including few patients and exclusively observational studies.
10. Recommendations. The following are the authors' recommendations:
    • All patients with acute aortic pathologies should receive medical therapy to control pain and blood pressure.
    • Type A acute aortic pathologies require immediate open surgical repair, although endovascular approaches are under investigation.
    • Acute pathologies of the descending aorta managed medically or with endovascular procedures are associated with lower early mortalities than those managed with open surgical procedures. Although medical and endovascular outcomes appear similar, existing literature is affected by selection bias in which sicker, higher-risk patients with uncomplicated type B pathologies more often undergo TEVAR compared to medical therapy.
    • Complicated IMH should be treated with open surgical intervention if type A, and TEVAR if type B.

Keywords: Aneurysm, Dissecting, Aortic Aneurysm, Aortic Aneurysm, Thoracic, Cardiac Surgical Procedures, Echocardiography, Transesophageal, Endovascular Procedures, Hematoma, Hypertension, Ischemic Attack, Transient, Magnetic Resonance Imaging, Pulmonary Disease, Chronic Obstructive, Renal Insufficiency, Chronic, Smoking, Stroke, Tomography, Vasa Vasorum

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