Aortic aneurysm

An aortic aneurysm is a general term for any swelling (dilatation or aneurysm) of the aorta, usually representing an underlying weakness in the wall of the aorta at that location. While the stretched vessel may occasionally cause discomfort, a greater concern is the risk of rupture, which causes severe pain; massive internal hemorrhage; and, without prompt treatment, results in a quick death.

Classification

Aortic aneurysms are classified by where on the aorta they occur; aneurysms can appear anywhere. An aortic root aneurysm, or aneurysm of sinus of Valsalva, appears on the sinuses of Valsalva or aortic root. Thoracic aortic aneurysms are found on the thoracic aorta; these are further classified as ascending, aortic arch, or descending aneurysms depending on the location on the thoracic aorta involved. Abdominal aortic aneurysms, the most common form of aortic aneurysm, are found on the abdominal aorta, and thoracoabdominal aortic aneuryms involve both the thoracic and abdominal aorta.

Pathology

The physical change in the aortic diameter can occur secondary to trauma, infection, an intrinsic defect in the protein construction of the aortic wall, or due to progressive destruction of aortic proteins by enzymes.

Signs, symptoms and diagnosis

Most intact aortic aneurysms do not produce symptoms. As they enlarge, symptoms such as abdominal pain and back pain may develop. Compression of nerve roots may cause leg pain or numbness. Untreated, aneurysms tend to become progressively larger, although the rate of enlargement is unpredictable for any individual. Rarely, clotted blood which lines most aortic aneurysms can break off and result in an embolus. They may be found on physical examination. Medical imaging is necessary to confirm the diagnosis. Symptoms may include: anxiety or feeling of stress; nausea and vomiting; clammy skin; rapid heart rate.

Abdominal aortic aneurysm

Abdominal aortic aneurysms, hereafter referred to as AAAs, are the most common type of aortic aneurysm. One reason for this is that elastin, the principal load-bearing protein present in the wall of the aorta, is reduced in the abdominal aorta as compared to the thoracic aorta (nearer the heart). Another is that the abdominal aorta does not possess vasa vasorum, hindering repair. Most are true aneurysms that involve all three layers (tunica intima, tunica media and tunica adventitia), and are generally asymptomatic before rupture.

The prevalence of AAAs increases with age, with an average age of 65-70 at the time of diagnosis. AAAs have been attributed to atherosclerosis, though other factors are involved in their formation.

An AAA may remain asymptomatic indefinitely. There is a large risk of rupture once the size has reached 5 cm, though some AAAs may swell to over 15 cm in diameter before rupturing. Before rupture, an AAA may present as a large, pulsatile mass above the umbilicus. A bruit may be heard from the turbulent flow in a severe atherosclerotic aneurysm or if thrombosis occurs. Unfortunately, however, rupture is usually the first hint of AAA. Once an aneurysm has ruptured, it presents with a classic pain-hypotension-mass triad. The pain is classically reported in the abdomen, back or flank. It is usually acute, severe and constant, and may radiate through the abdomen to the back.

The diagnosis of an abdominal aortic aneurysm can be confirmed at the bedside by the use of ultrasound. Rupture could be indicated by the presence of free fluid in potential abdominal spaces, such as Morison's pouch, the splenorenal space (between the spleen and left kidney), subdiaphragmatic spaces (underneath the diaphragm) and peri-vesical spaces. A contrast-enhanced abdominal CT scan is needed for confirmation.

Only 10-25% of patients survive rupture due to large pre- and post-operative mortality. Annual mortality from ruptured abdominal aneurysms in the United States alone is about 15,000. Another important complication of AAA is formation of a thrombus in the aneurysm.

Medical treatment

Medical therapy of aortic aneurysms involves strict blood pressure control. This does not treat the aortic aneurysm per se, but control of hypertension within tight blood pressure parameters may decrease the rate of expansion of the aneurysm.

Surgical treatment

The definitive treatment for an aortic aneurysm is surgical repair of the aorta. This typically involves opening up of the dilated portion of the aorta and insertion of a synthetic (Dacron or Gore-tex) patch tube. Once the tube is sewn into the proximal and distal portions of the aorta, the aneurysmal sac is closed around the artificial tube. Instead of sewing, the tube ends, made rigid and expandable by nitinol wireframe, can be much more simply and quickly inserted into the vascular stumps and there permanently fixed by external ligature.

The determination of when surgery should be performed is complex and case-specific. The overriding consideration is when the risk of rupture exceeds the risk of surgery. The diameter of the aneurysm, its rate of growth, the presence or absence of Marfan Syndrome or similar connective tissue disorders, and other coexisting medical conditions are all important factors in the determination.

A rapidly expanding aneurysm should be operated on as soon as feasible, since it has a greater chance of rupture. Slowly expanding aortic aneurysms may be followed by routine diagnostic testing (ie: CT scan or ultrasound imaging). If the aortic aneurysm grows at a rate of more than 1 cm/year, surgical treatment should be electively performed.

The current treatment guidelines for abdominal aortic aneurysms suggest elective surgical repair when the diameter of the aneurysm is greater than 5 cm. However, recent data suggests medical management for abdominal aneurysms with a diameter of less than 5.5 cm.

Endovascular treatment of AAA

In the recent years, the endoluminal treatment of Abdominal Aortic Aneurysms has emerged as a minimally invasive alternative to open surgery repair. The first endoluminal exclusion of an aneurysm took place in Argentina by Dr. Parodi and his colleagues in 1991. The endovascular treatment of aortic aneurysms involves the placement of an endo-vascular stent via a percutaneous technique (usually through the femoral arteries) into the diseased portion of the aorta. This technique has been reported to have a lower mortality rate compared to open surgical repair, and is now being widely used in individuals with co-morbid conditions that make them high risk patients for open surgery. Some centers also report very promising results for the specific method in patients that do not constitute a high surgical risk group.

There have also been many reports concerning the endovascular treatment of ruptured Abdominal Aortic Aneurysms, which are usually treated with an open surgery repair due to the patient's impaired overall condition. Mid-term results have been quite promising. However, according to the latest studies, the EVAR procedure doesn't carry any overall survival benefit.

Endovascular treatment of other aortic aneurysms

The endoluminal exclusion of aortic aneurysms has seen a real revolution in the very recent years. It is now possible to treat thoracic aortic aneurysms, abdominal aortic aneurysms and other aneurysms in most of the body's major arteries (such as the iliac and the femoral arteries) using endovascular stents and avoiding big incisions. Still, in most cases the technique is applied in patients at high risk for surgery as more trials are required in order to fully accept this method as the gold standard for the treatment of aneurysms.

Prevention

Attention to patient's general blood pressure, smoking and cholesterol risks helps reduce the risk on an individual basis. There have been proposals to introduce ultrasound scans as a screening tool for those most at risk: men over the age of 65. The tetracycline antibiotic Doxycycline is currently being investigated for use as a potential drug in the prevention of aortic aneurysm due to its metalloproteinase inhibitor and collagen stabilising properties.

Research

Stanford University is conducting research to gather information on AAA risk factors, and to evaluate the effectiveness of an exercise program at preventing the growth of small AAAs in older individuals