08-19-2018, 04:32 PM
Aortic dissection occurs when a tear in the intimal layer of the aorta allows blood to enter a new, false lumen between the intima and media. Blood can subsequently travel proximally or distally within this lumen.
Risk factors for aortic dissection:
• Hypertension -- major (and most common) risk factor
• Congenital connective tissue disorders (e.g., Marfan syndrome)
• Bicuspid aortic valve
Aortic dissections in older adults (40-60 years of age) are most commonly due to hypertension, whereas aortic dissections in younger adults are most commonly due to connective tissue disorders.
Congenital connective tissue disorders that can be associated with aortic dissection include:
• Marfan syndrome
• Ehlers-Danlos syndrome
• Impaired copper metabolism
Patients with aortic dissection present with sudden-onset, tearing chest pain that radiates to the back between the scapulae and migrates inferiorly as the dissection progresses soon after the onset of the pain.
Patients may also have unequal pulses in their upper extremities due to (partial) occlusion of the left subclavian artery or brachiocephalic trunk.
CT angiography is most commonly used to image patients with a suspected aortic dissection who are hemodynamically stable. Identification of two aortic lumens (true and false lumens) or an intimal flap indicates aortic dissection.
Chest x-ray of patients with aortic dissection classically shows a widening of mediastinum.
Stanford type A (proximal) aortic dissections are most commonly treated with emergency surgery, whereas Stanford type B (distal) aortic dissections are most commonly treated with β-blockers, and subsequently vasodilators (e.g., sodium nitroprusside).
Two types of aortic dissection include:
• Stanford type A (proximal), must involve the ascending aorta, and may extend to involve the aortic arch and descending aorta
• Stanford type B (distal), only involves the descending aorta
Stanford type A (proximal) aortic dissections are more common and more dangerous than Stanford type B (distal) aortic dissections. Stanford type A dissections are more dangerous because a dissection of the ascending aorta may extend to involve the:
• Carotid arteries leading to stroke
• Coronary arteries leading to myocardial infarction
• Pericardial sac leading to cardiac tamponade
Familial thoracic aortic aneurysm, an autosomal dominant disorder, leads to cystic medial degeneration; a breakdown of collagen, elastin, and smooth muscle in the aortic wall. It may predispose to aortic dissection, which is initiated by a transverse or oblique tear in the aortic intima.
Under systemic pressures, this initial intramural aortic hemorrhage quickly gives rise to an unstable medial hematoma which may:
• Extend within the media proximally toward the heart and/or distally toward the lower extremities
• Rupture through the adventitia into the:
• Pericardial sac can lead to cardiac tamponade
• Pleural or peritoneal cavities leading to massive hemorrhage