Thoracic Aortic Aneurysm

Disease of the aorta is the 12th leading cause of death in the United States. Aneurysms of the aorta can occur in the chest or abdomen, or both at the same time. The aorta is the main blood vessel carrying arterial blood from the heart to the rest of the body. It begins in the chest and ends in the abdomen, and along its course, it branches off to the head and neck, arms, chest, abdomen (including the kidneys, liver and intestines) and finally the legs.

An aneurysm is defined as an enlargement of the arterial wall of more than 150 percent of the diameter of the normal artery. The artery wall is made out of special elastic proteins that can withstand the blood's pressure and be pliable at the same time. The normal consistency of the artery is like a cooked noodle, but when it degenerates and hardens, it becomes stiff and brittle, like an uncooked noodle. This process occurs because of arteriosclerosis, or hardening and degeneration of arteries.

The term arteriosclerosis comes from the Greek words for blood vessel and hardening. Another term used is atherosclerosis: Athero means gruel and sclerosis means hard.

This can lead to enlargement of the artery because of the breakdown in its structure. In turn, this breakdown leads to weakness in the wall, thus leading to further enlargement. In some cases of aortic aneurysm, there is no atherosclerosis, but instead there is an inherited abnormality of the blood vessel wall that causes aneurysms to form, such as a condition known as Marfan syndrome.

When the artery is enlarged, it is like a balloon; The larger it gets, the weaker it is and the higher the chance of its rupturing. Ruptured aneurysms can kill suddenly.

Some people are fortunate enough to survive the first rupture or leak. This is like a punctured tire, which may leak slowly, often allowing you to repair it and fill it before it goes flat, but if the hole is large enough, the tire will go flat immediately. There are other diseases that can occur in the aorta, such a tear from blunt trauma (most commonly high-speed car accidents), dissection, inflammation (Takayasu's arteritis) or infection. Most patients with TAA have no symptoms, although some patients will experience chest or back pain. If the pain is excruciating, then it is usually associated with a rupture or dissection. In other less common situations, symptoms are often vague, such as shortness of breath, loss of consciousness, high or low blood pressure, heart rhythm irregularity, fluid or blood in the chest or a dull ache.

Thoracic aneurysms generally occur in elderly populations. It is estimated that six to 10 per 100,000 individuals have a thoracic aortic aneurysm (TAA). If the TAA is left untreated, it will probably continue to enlarge. If a TAA ruptures or leads to an aortic dissection, it can kill a person immediately. The death rate from a ruptured TAA can be up to 94 percent. Therefore, most surgeons and specialists recommend repair of a TAA before it ruptures.

The diagnosis of TAA can be made by one of several ways. Sometimes, a plain chest x-ray will hint to its presence. The best methods to image the thoracic aorta are either a CT scan or MRI. Both of these tests can provide comprehensive information about the size of the aneurysm and its relationship to other structures; this information enables the vascular specialist to recommend the most appropriate treatment plan. If the aneurysm is too small to fix, usually a surveillance program to monitor the growth of the aneurysm is recommended for the patient so that the physician can recommend intervention at the right time. There are other tests that can be used to diagnose or monitor a TAA, including an angiogram or echocardiogram.

The treatment options for a TAA are largely dependent on the size of the aneurysm, whether it is causing symptoms, and where the aneurysm is located. For example, if the TAA is in the ascending aorta (the first portion of the aorta as it goes out from the heart) or in the transverse arch (the second part of the aorta which gives off branches to the head, neck and arms), then the only treatment available is surgery. This procedure involves opening the chest, just like for patients having heart bypass surgery, and replacing the diseased aorta with a Dacron graft, which is a synthetic (man-made) material, used to replace normal body tissues. Experimental treatments with stent grafts for a TAA are available only in highly specialized research centers. If the TAA is located in the descending aorta (the third part of the aorta that starts in the upper chest and ends at the diaphragm), there are two options available: the conventional open repair with a Dacron graft or the stent graft repair.

When a patient undergoes the open TAA repair, the procedure is performed under general anesthesia. The left side of the chest is opened and the surgeon sews a Dacron graft to replace the diseased part of the aorta. This serious operation carries a mortality rate of five to 10 percent in the best centers. There are also many complications that can occur with this operation, such as paralysis, kidney failure, pneumonia, wound infections and blood clots. Many of the patients who need a TAA repair have other chronic illnesses putting them to be at higher risk for complications.

Since 2005, many centers in the United States have been able to offer patients a newer method of repairing a TAA which is called thoracic endovascular aneurysm repair (TEVAR). In this procedure, instead of opening the chest to sew in a graft, a stent graft is placed through an incision in the groin across the aneurysm to treat the diseased aorta. This procedure can be performed in less time, with less blood loss, a shorter hospital stay and faster recovery. The procedure has to be done by specialists trained to perform this, and it requires special x-ray imaging to place the graft. Not every patient can undergo this type of procedure. In many cases, additional preparatory procedures have to be performed to facilitate TEVAR. Once the procedure is completed, patients still need to see their physician for follow-up x-rays to make sure that the stent graft is still working properly. Because this is a relatively new procedure, the durability of TEVAR is not clear as there is not yet long-term followup information on patients treated with this approach (i.e., over 10 to 15 years). There are some patients who may be too ill to be considered for any type of repair.

About the Author: Ashraf M. Mansour, MD, FACS is a practicing vascular surgeon at Spectrum Health in Grand Rapids, Michigan. He is Director of the vascular surgery fellowship and Professor of Surgery, Michigan State University.

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