Aortic Dissection

The aorta is the large blood vessel that carries blood away from the heart, down through the chest and abdomen where it ends before dividing into two large branches which continue into the legs.  Throughout its course the aorta has branches that supply blood to various body parts and organs.  The normal diameter of the aorta is approximately one inch.  An aneurysm is an enlargement of the aorta, usually confined to a particular section.  A dissection is a tear in the wall of the aorta.  Dissections of the aorta do not always occur in sections affected by aneurysms.

Aortic Aneurysm Types

Causes

The causes of aneurysms are not completely known.  They are more commonly seen in individuals with other atherosclerotic risk factors, especially hypertension.  Smokers, in particular, have a higher likelihood of developing abdominal aortic aneurysms.  It is likely that atherosclerosis contributes to the development of aneurysms.  This may cause a weakening of the wall of the aorta, making it more likely to enlarge under the pressure within the aorta.  A family history of aneurysms increases the likelihood that an individual may develop an aneurysm.  There are some other conditions not related to atherosclerosis that are associated with an increased probability of aneurysm formation.  Marfan's Syndrome and trauma to the chest are some examples. 

Diagnosis

Thoracic aneurysms are often suspected when chest or back X-rays are done for other reasons.  Detecting them on physical examination is difficult although there can be clues such as a difference in blood pressure between the right and left arm and some types of heart murmurs.  Other tests that can detect thoracic aneurysms are CT scans, echocardiograms ,  transesophogeal echocardiograms and MRI.

Abdominal aortic aneurysms can be detected more readily on physical examination but few will be, probably less than 15% of all AAAs.  Many are discovered when testing is done to evaluate suspicious symptoms. Many are discovered "by accident" when test such as X-rays are done for other problems such as low back pain. Common tests for AAA detection include ultrasound, CT and MRI.  Unfortunately, many are diagnosed only after they rupture and cause severe symptoms or shock (dangerously low blood pressure and collapse) due to bleeding.  This is a medical and surgical emergency.  There is evidence to support to the use of "screening" tests in patients at high risk for AAA since so few can be detected on physical exam and so many patients present with a ruptured AAA as their first symptom.

Symptoms of Aneurysms

Thoracic aneurysms (TAA) rarely cause symptoms unless they are associated with a dissection, in which case they cause pain, usually very severe in intensity. Symptoms of thoracic aneurysms alone can include chest or back discomfort, discomfort in the neck or jaw, cough, hoarseness, difficulty swallowing and difficulty breathing. Most are discovered when tests such as chest X-rays and echocardiograms are done for other reasons. Undetected TAAs are more likely to enlarge further and rupture or dissect. The mortality of an aortic dissection is very high.

Abdominal aneurysms (AAA) most commonly cause abdominal or back discomfort. Some individuals may feel a strong abdominal pulse. Many are discovered incidentally when tests such as ultrasounds, CT scans or even regular X-rays are done for other reasons. If individuals present with a ruptured AAA the mortality is very high emphasizing the importance of early detection and treatment.

Treatment

The most important aspect of treatment is early detection followed by efforts to prevent further enlargement in those that do not require immediate surgery to correct.  This is combined with close surveillance utilizing periodic testing with ultrasound or X-rays (usually about every six to twelve months) to monitor for progression.  In the absence of severe symptoms or dissection the size of the aneurysm is usually what determines when procedures are needed to prevent rupture.  In general, when thoracic aneurysms reach a diameter of 6 cm (slightly less than 2.5 inches) they require "repair" procedures.  In general, when abdominal aneurysms reach a size of 4.5 cm "repair" needs to be considered.  These are general guidelines and individual characteristics need to be considered, including how fast the aneurysm is enlarging.  The physician, along with the patient, will take multiple factors into consideration when determining the best course of treatment.

Medical Treatment:  If detected before surgery is necessary, efforts to prevent progression of aneurysms are directed at aggressive treatment of atherosclerosis risk factors.  Smoking must be discontinued.  Blood pressure control, in particular, is important and often medications are chosen to not only lower blood pressure in general, but also keep the heart rate controlled (beta-blockers).

Percutaneous surgical "repair":  Endovascular is a method of placing a "fabric" coated stent into the aorta to prevent further enlargement and rupture.  This is done by inserting a specially designed stent into the aneurysm through a small incision in the arteries located in the groin.  This technique has been shown to be safe and effective in appropriately selected patients.  In general, the hospital stay following this type of repair is shorter.

Surgical "repair":  In some patients surgical repair is preferred.  This usually involves replacing the aneurysm with an artificial "tube".  Emergency repair of a ruptured TAA or AAA is usually done with surgery.