Thoracic Aortic Aneurysms (TAA)

Author
Jacques G. Tittley

Title
Thoracic Aortic Aneurysms (TAA)

What is a thoracic aortic aneurysm?
Arteries are designed to withstand high pressure. An aneurysm is a dilatation (ballooning) of an artery, which can burst and lead to life threatening hemorrhage.    The aorta is the body's main artery, originating from the heart in the chest. In the thoracic (chest) cavity, it  forms an arch, similar to a candy cane, and  is divided in three sections: ascending , transverse and descending thoracic aorta. Upon leaving the chest, the aorta continues it's course into the abdomen, and delivers blood to the rest of the body. Most aortic aneurysms are located in the abdominal cavity (90%). Less frequently, they can occur in the thoracic aorta, in either the ascending, arch, or descending section.

What causes thoracic aortic aneurysm?
The most common cause for a TAA is weakening of aortic wall, leading to localized dilatation or bulging. Atherosclerosis (ironicaly also known as "hardening of the arteries") causes degeneration and aneurysm formation. Family history, smoking, male gender, high blood, high cholesterol, high blood pressure and previous stroke also are identified risk factors. In young people (<40yrs.), thoracic aneurysms are often associated with connective tissue disorders such as Marfan's  or Ehlers-Danlos syndromes. Other conditions include infection, trauma, and aortic dissection, which is when a tear occurs between the layers of the aortic wall, and blood flows within the wall.

What are the symptoms of  thoracic aortic aneurysm?
The majority of TAAs are aymptomatic. They are commonly discovered during a chest X-ray or CT scan done for another reason. On occasion, thoracic aneurysms can be discovered during an ultrasound of the heart (echocardiography). Acute or chronic symptoms can range from chest, neck, jaw or back pain, to life threatening bleeding and shock. Occasionnaly, a thoracic aneurysm can compress on adjacent chest structures and  cause hoarseness, coughing or problems swallowing.

Diagnosis and tests for thoracic aortic aneurysm
A simple chest X-ray can usually detect an abnormality in the thoracic aorta, but actual measurement of the aortic diameter can only by performed reliably with either Computerized Tomography (CT scan) or Magnetic resonance (MRI). Echocardiography (ultrasound of the heart) can also be reliable, but is more invasive.

Lifestyle modification for thoracic aortic aneurysm
Although most aortic specialists recommend no heavy lifting, exercising in moderation and avoiding emotional extremes,  there is very little scientific evidence for this. Much depends on the size of the aneurysm as the patient is being followed within a surveillance program. Logically, the closer the aneurysm diameter approaches operative threshold, the more closely the above suggestions about lifestyle should be followed. Travel insurrance can be difficult to obtain and often depends  on insurance policy wording. Fitness to drive  restrictions can also apply.

Non-surgical and medical management for thoracic aortic aneurysm
The mainstay of non-surgical management  for all aortic aneurysms is conservative, otherwise known as  "watchful waiting" or surveillance. Your doctor will measure your aneurysm at pre-determined intervals to make sure it has not reached a critical size or growing to fast. The prescribed time intervals between measurements may change. Unlike abdominal aortic aneurysms, which can easily be followed with periodic ultrasound measurements, the diameter and growth rate of TAAs can only be measured accurately by either CT scan or MRI. No medication has proven effective in slowing the growth rate of aneurysms. Medications to control high blood pressure and cessation of smoking are recommended.

Guidelines for Intervention for thoracic aortic aneurysm
Any patient with an acutely  symptomatic  thoracic aortic aneurysm (see above) requires immediate attention. The decision to treat an asymptomatic thoracic aortic aneurysm depends on many factors, including aneurysm size, it's location, the extent of the intervention involved, and the ability of the patient to withstand such a procedure. As aneurysms get bigger, their risk of rupture increases. Intervention should be considered when the diameter of a thoracic aortic aneurysm reaches 5.5cms in men, and 5.0 in women. Smaller aneurysms under surveillance typically grow by 10% per year. Faster growing aneuryms should be considerd for intervention sooner than the usual operative threshold.

Surgical treatment for thoracic aortic aneurysm
The traditional treatment for all thoracic aneurysms has been open surgical resection and replacement with Dacron (plastic cloth) graft. For the most part, aneurysms of the ascending thoracic aorta and  aortic arch continue to be repaired in this fashion through an incision of the breast bone and cardiopulmonary bypass (heart-lung machine). The descending thoracic aorta can also be repaired surgically through an incision between the ribs of the left chest.
All the above operations have significant associated complications. The evolution of  lesser invasive endovascular techniques are gradually replacing open surgical interventions.

Endovascular Treatment for thoracic aortic aneurysm
Endovascular, meaning repairing from within the blood vessels, consist of installing  a "liner" inside aortic aneurysms. The high arterial pressure is assumed by the stent graft and depressurizes the aneurysm, reducing the risk of bursting. A cloth covered metallic stent contained within a pencil size  delivery system is introduced through two small incisions in the groin arteries and deployed in the chest aneurysm with X-ray control. Endovscular repair is much less invasive than open surgical repair, but does not eliminate the aneurysm. Therefore, permanent  ongoing follow-up and surveillance is required. As this technology evolves, ascending and arch aneurysms will be repaired this way.

When should I see my doctor?
Anyone with an identified thoracic aortic aneurysm should be carefully monitored in a scheduled surveillance program, managed  by either your doctor or an aortic specialist. Patients who experience any acute symptoms suggestive of a thoracic aortic aneurysm (see above) should be assessed immediately in an institution that has access to advanced imaging facilities (CT scan or MRI) and is familiar with thoracic aortic pathologies.

References and Resources
Wikipedia
http://en.wikipedia.org/wiki/Thoracic_aortic_aneurysm
St. Luke's School of Medicine http://www.slrctsurgery.com/Thoracic%20aortic%20aneurysms.htm
Canadian Medical Association - Fitness to drive guidelines
http://www.cma.ca/index.php/ci_id/18223/la_id/1.htm

Comments/notes from the author

Thoracic aortic aneurysms are not common but must be managed appropriately by an aortic specialist. The constant evolution in endovascular modalities is very promissing to further reduce the complications associated with interventions.