Types of Aortic Dissection

The aorta—a candy cane–shaped blood vessel originating in the chest at the top of the heart and extending into the abdomen—is the largest artery in the body. Like other arteries, it carries oxygen-rich blood from the heart to the rest of the body. The walls of the aorta consist of three layers that give it strength.

An aortic dissection, or tear in the aorta, typically occurs when the inner layer of the artery’s wall weakens. A small tear forms in this layer, and, if left untreated, it can enlarge.

Blood can pass through the tear into the middle layer of the wall, causing the layers to separate from one another, or dissect. This can lead to the formation of a new channel, called a false lumen, between the two layers. This false lumen can extend from the tear to the lowest part of the aorta, preventing blood from flowing properly to the rest of the body.

The separation of the inner layer of the aorta forms a flap, or septum, which can have multiple holes, known as reentry tears, that have a Swiss cheese appearance. These tears allow blood to flow between the true lumen, or natural passageway, and the false lumen. If the flap doesn’t peel away from the aorta, blood can pool in the false lumen.

Over time, the blood in the false lumen can back up and clot, cutting off blood flow to other organs and further weakening the aortic wall. Sometimes, the blood breaks through the outer layer of the aorta, causing a life-threatening loss of blood and drop in blood pressure that requires immediate surgery.

Aortic dissection can lead to serious complications, including heart attack, kidney failure, stroke, paralysis, and intestinal ischemia, in which blood vessels to the intestines become blocked. It can also cause lower extremity ischemia, or blockages in the blood vessels of the legs.

Because the risks and appropriate treatments can be markedly different depending on the type of aortic dissection, it is crucial to accurately diagnose this condition. Doctors at NYU Langone diagnose the type of aortic dissection based on the location of the tear and the duration of the symptoms. There are two types of aortic dissection, type A and type B.

Type A Aortic Dissection

If the aortic dissection occurs in the ascending aorta, the curved part of the aorta that extends upward from the heart, it’s called a type A aortic dissection. A type A tear may extend along the upper part of the aorta and down toward the abdomen.

Type A is more common than type B. It’s also more dangerous, because it’s more likely to cause the aorta to rupture, leading to a potentially fatal heart condition.

Although this type of dissection sometimes causes no symptoms, it is more often accompanied by shortness of breath and a sudden, severe, sharp pain that feels like a tearing in the chest and upper back. It requires immediate surgery.

Type B Aortic Dissection

A type B aortic dissection originates in the descending aorta, which extends from the arch at the top of the ascending aorta—the part that extends upward from the heart—in the chest to the bottom section of the aorta, also known as the abdominal aorta.

This type of dissection is usually treated with medications and monitoring by a doctor, because it rarely causes life-threatening side effects. Occasionally, type B dissections can reduce or block blood flow to organs, such as the kidneys and the intestines, requiring surgery.

Symptoms may include high blood pressure and a severe, sharp back pain that can feel like it is extending into the chest or abdomen.

Acute Aortic Dissection

Both type A and type B aortic dissections are further diagnosed by doctors as being either acute or chronic. The majority of aortic dissections are acute, meaning the tear causes symptoms immediately and can be life threatening.

Acute aortic dissection causes sudden chest or back pain or both. Because the condition can lead to a rupture of the aorta, it requires immediate medical attention, usually surgery.

Chronic Aortic Dissection

Sometimes symptoms of an aortic dissection are vague and nonspecific and may go unnoticed until the tear begins to cause other complications. When these symptoms occur, or if imaging tests show signs that the condition has been present two weeks or longer, it is called chronic aortic dissection. Most chronic aortic dissections are type B.

After you receive a diagnosis, your doctor monitors the chronic dissection with CT scans or a type of MRI scan called a magnetic resonance angiogram. These imaging tests can reveal a rapid expansion of the aorta, which can signify a blood clot or an aortic aneurysm, in which the aorta bulges, necessitating surgery. Medications are often prescribed to help reduce the flow of blood against the aortic wall.

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