What is a thoracic aneurysm?
A thoracic aortic aneurysm is a widening (bulging) of part of the wall of the aorta, the body’s largest artery. Only half of patients with thoracic aortic aneurysms notice symptoms. Most thoracic aneurysms are detected when imaging studies (chest x-rays, CT scans, MRI, etc) are being obtained for unrelated reasons.
The aorta is the major artery which arises from the heart. It carries all the blood that is pumped out of the heart and distributes it via its many branches to all the organs of the body. The aorta is divided into 4 portions: 1) the ascending aorta , 2) the aortic arch 3) the descending thoracic aorta and 4) the abdominal aorta.
An aortic aneurysm is an enlargement of a weakened area of the aorta. Aneurysms which involve the ascending aorta, aortic arch and descending thoracic aorta are termed “thoracic aortic aneurysms.” Aneurysms in these regions are prone to rupture once they reach a certain size. Fifty percent of patients who experience a rupture of a thoracic aortic aneurysm die before reaching the hospital. Only about 20 to 30 percent of patients who get to the hospital with a ruptured thoracic aortic aneurysm survive. For this reason, it is crucial to treat large aneurysms early, in order to prevent their rupture.
The thoracic aorta is also prone to dissection, or a tearing of the wall of the aorta. When this occurs in the ascending aorta or aortic arch it represents a life threatening emergency which is typically treated with emergency surgery. When a dissection involves the descending thoracic or abdominal aorta, emergency treatment is still required but this rarely includes surgery. Control of the blood pressure and adequate pain control typically results in healing of the injury. However, dissections of the descending and abdominal aorta do weaken the wall of the aorta and are prone to aneurysm formation. Close follow-up with an aneurysm specialist is recommended.
What are the symptoms of a thoracic aneurysm?
When aortic aneurysms reach larger sizes, the symptoms are typically based on the location of the aneurysm. Ascending aortic aneurysms can cause dilatation and leakage of the aortic valve. This can result in shortness of breath or even heart failure if the leakage is severe.
Aortic arch aneurysms can produce upper chest and back pain. However, when large, these aneurysms can compress both the esophagus and the airway resulting in difficulty swallowing and hoarseness.
Descending thoracic aneurysms are mostly asymptomatic, but can occasionally cause back pain. In contrast, abdominal aneurysms may cause a pulsating feeling in the abdomen. Abdominal and back pain may also be present if the aneurysm increases in size. Most of the symptoms associated with stable thoracic aneurysms are vague and non-specific. However, rupture or dissection of these aneurysms produces dramatic symptoms. A ripping sensation within the chest accompanied by severe pain in the back between the shoulder blades is the most typical complaint during thoracic aortic dissection or rupture. Dizziness, fainting, difficulty walking and speaking can all accompany this acute event. Patients with known aortic aneurysms experiencing such symptoms need to contact their physician or surgeon immediately and go to the nearest emergency room.
What causes a thoracic aneurysm?
Physicians and scientists believe that atherosclerosis causes thoracic aortic aneurysms. Atherosclerosis is the term used to describe hardening of the arteries. Your arteries are normally smooth and unobstructed on the inside but, as you age, they can become blocked through this process. Smoking, high blood pressure and high cholesterol are the primary causes of atherosclerosis. This disease typically results in blockages of arteries that deliver blood to the heart (coronary arteries), the legs (femoral arteries), or the brain (carotid arteries). The damage caused to the aortic wall by atherosclerosis can result in aneurysm formation.
A condition known as idiopathic cystic medial degeneration is the most common cause of ascending aortic aneurysms. The elastic fibers which make up the outer wall of the aorta normally break down as we age, making the aorta more prone to dilation. In some patients this process is accelerated resulting in early aneurysm formation. At the moment, we do not know the exact mechanisms involved in this process (hence the term idiopathic). Cystic medial degeneration can also be the cause of aortic arch and descending thoracic aneurysms.
Other known diseases exist that can weaken the layers of the aortic wall, increasing the risk of aneurysms. These diseases include Marfan’s syndrome, Ehlers-Danlos syndrome, syphilis, and tuberculosis. Trauma, such as a fall or rapid deceleration in a motor vehicle accident, can also be a cause of thoracic aneurysms and dissection.
What testing is required?
The risk of aneurysm rupture for aneurysms under 5.5-6.0 centimeters is quite small. There is not much benefit for surgical intervention for aneurysms of this size. Once the aneurysm reaches five cm., the risk of rupture may approximate ten percent per year. Under such circumstances most surgeons would advise repair of the aneurysm unless the patient has prohibitive medical risks against treatment. Although the endovascular treatment is safer than standard surgery most surgeons would still favor withholding this treatment until the aneurysm reaches 5.5-6.0 cm.
What treatment is available for a thoracic aneurysm?
Once an aneurysm is diagnosed, strict control of the blood pressure and avoidance of smoking are two interventions which may prevent growth. At present, there are no medications which can either shrink the aneurysm or prevent its growth.
Operative treatment depends on the location of the aneurysm. For patients with aneurysms of the ascending aorta or aortic arch, surgery to replace the aorta is recommended if the aneurysm is larger than 5-6 centimeters. The aorta is replaced with a fabric substitute. This is major surgery that requires a heart-lung machine. If the aortic arch is involved, a specialized technique called “circulatory arrest” — a period without blood circulation while on life support — may be necessary. If only the aortic arch is involved, hybrid procedures utilizing stents, may be an option, thereby avoiding “circulatory arrest.”
There are two options for patients with aneurysms of the descending thoracic aorta. If the aneurysm is larger than 6 centimeters, major surgery is done to replace the aorta with a fabric substitute. Following the surgery, you may stay in the hospital for 5 to 7 days. If your aneurysm is extensive or complex, or if you have other conditions such as heart, lung or kidney disease, you may require 2 to 3 months for a complete recovery. Endovascular stenting is a less invasive option. Endovascular stent-graft repair requires a shorter recovery time than open aneurysm repair, and your hospital stay is reduced to 2 or 3 days. However, not all patients with descending thoracic aneurysms are candidates for stenting.
Both standard open surgery and stenting procedures carry significant risks, although these are often more common and more severe with open surgery than with stenting. The main concern is that of postoperative lower limb paralysis. Stroke and kidney failure are two of the other major complications. Whatever technique is chosen, it is important to select a surgeon that has experience in treating these conditions since they are uncommon and technically challenging.