Aortic dissection

Aortic dissection is a tear of the aorta (the largest artery of the body). This tear causes blood to flow between the layers of the wall of the aorta and dissects the layers apart. Aortic dissection is an extremely serious medical emergency and can quickly lead to death.

Pathophysiology

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Aortic dissection

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An echocardiogram displaying the true lumen and false lumen of an aortic dissection. In the image to the left, the intimal flap can be seen separating the two lumens. In the image to the right, color flow during ventricular systole suggests that the upper lumen is the true lumen.

Related Topics:
Echocardiogram - Systole

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The initiating event in an aortic dissection is a tear in the intimal lining of the aorta. Due to the high pressures in the aorta, blood enters the media at the point of the tear. The force of the blood entering the media causes the tear to extend. It may extend proximally (closer to the heart) or distally (away from the heart) or both. The blood will travel through the media, creating a false lumen (the true lumen is the normal conduit of blood in the aorta). Separating the false lumen from the true lumen is a layer of intimal tissue. This tissue is known as the intimal flap.

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The vast majority of aortic dissections originate with an intimal tear in either the ascending aorta (65%), the aortic arch (10%), or just distal to the ligamentum arteriosum in the descending thoracic aorta (20%).

Related Topics:
Ascending aorta - Ligamentum arteriosum

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As blood flows down the false lumen, it may cause secondary tears in the intima. Through these secondary tears, the blood can re-enter the true lumen.

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While it is not always clear why an intimal tear may occur, quite often it involves degeneration of the collagen and elastin that make up the media. This is known as cystic medial necrosis and is most commonly associated with Marfan syndrome and is also associated with Ehlers-Danlos syndrome.

Related Topics:
Marfan syndrome - Ehlers-Danlos syndrome

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In about 13% of aortic dissections, there is no evidence of an intimal tear. It is believed that in these cases the inciting event is an intramural hematoma (caused by hemorrhage within the media). Since there is no direct connection between the true lumen and the false lumen in these cases, it is difficult to diagnose an aortic dissection by aortography if the etiology is an intramural hematoma. An aortic dissection secondary to an intramural hematoma should be treated the same as one caused by an intimal tear.

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