Aortic dissection

Aortic dissection is a tear in the wall 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 a medical emergency and can quickly lead to death, even with optimal treatment. more...

Overview

As with all other arteries, the aorta is made up of three layers. The layer that is in direct contact with the flow of blood is the tunica intima, commonly called the intima. This layer is made up of mainly endothelial cells. Just deep to this layer is the tunica media, known as the media. This "middle layer" is made up of smooth muscle cells and elastic tissue. The outermost layer (furthest from the flow of blood) is known as the tunica adventitia or the adventitia. This layer is composed of connective tissue.

In an aortic dissection, blood penetrates the intima and enters the media layer. The high pressure rips the tissue of the media apart, allowing more blood to enter. This can propagate along the length of the aorta for a variable distance, dissecting either towards or away from the heart or both. The initial tear is usually within 10 cm of the aortic valve.

The risk in aortic dissection is that the aorta may rupture, leading to massive blood loss resulting in death.

Classification systems

Several different classification systems have been used to describe aortic dissections. The systems commonly in use are either based on the anatomy of the dissection or the duration of onset of symptoms prior to presentation.

DeBakey classification system

The DeBakey system is an anatomical description of the aortic dissection. It categorizes the dissection based on where the original intimal tear is located and the extent of the dissection (localized to either the ascending aorta or descending aorta, or involves both the ascending and descending aorta.

• Type I - Originates in ascending aorta, propagates at least to the aortic arch and often beyond it distally.
• Type II – Originates in and is confined to the ascending aorta.
• Type III – Originates in descending aorta, rarely extends proximally.

Pathophysiology

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.

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%).

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