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CT reconstruction image of an abdominal aortic aneurysm
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An aortic aneurysm is a general term for an enlargement (dilation) of the aorta to greater than 1.5 times normal size. They are most commonly located in the abdominal aorta, but can also be located in the paravisceral or thoracic aorta. Aortic aneurysms cause weakness in the wall of the aorta and increase the risk of aortic rupture. The aneurysm usually is asymptomatic, but may occasionally cause pain in the back, and is considered a sign of impending rupture. When rupture occurs, massive internal hemorrhage results, and, unless treated immediately, shock and death can occur.
Aortic aneurysms are classified by their location on the aorta.
- An aortic root aneurysm, or aneurysm of the sinus of Valsalva.
- Thoracic aortic aneurysms are found within the chest; these are further classified as ascending, aortic arch, or descending aneurysms.
- Abdominal aortic aneurysms, "AAA" or "Triple A," the most common form of aortic aneurysm, involve that segment of the aorta within the abdominal cavity. Thoracoabdominal aortic aneurysms involve both the thoracic and abdominal aorta. There are other classifications that might help treatment.
Signs and symptoms
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.
Aneurysms can be found on physical examination. Medical imaging is necessary to confirm the diagnosis and to determine the anatomic extent of the aneurysm. In patients presenting with aneurysm of the arch of the aorta, a common sign is a hoarse voice from stretching of the left recurrent laryngeal nerve, a branch of the vagus nerve that winds around the aortic arch to supply the muscles of the larynx.
Abdominal aortic aneurysm
Abdominal aortic aneurysms (AAAs) are more common than their thoracic counterpart. 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. Another is that the abdominal aorta does not possess vasa vasorum, the nutrient-supplying blood vessels within the wall of the aorta. Most AAA are true aneurysms that involve all three layers (tunica intima, tunica media and tunica adventitia). 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.
The risk of rupture of an AAA is related to its diameter; once the aneurysm reaches about 5 cm, the yearly risk of rupture may exceed the risks of surgical repair for an average-risk patient. Rupture risk is also related to shape; so-called "fusiform" (long) aneurysms are considered less rupture prone than "saccular" (shorter, bulbous) aneurysms, the latter having more wall tension in a particular location in the aneurysm wall.
Before rupture, an AAA may present as a large, pulsatile mass above the umbilicus. A bruit may be heard from the turbulent flow in the aneurysm. Unfortunately, however, rupture may be the first hint of AAA. Once an aneurysm has ruptured, it presents with classic symptoms of abdominal pain which is severe, constant, and radiating to the back.
The diagnosis of an abdominal aortic aneurysm can be confirmed at the bedside by the use of ultrasound. Rupture may be indicated by the presence of free fluid in the abdomen. A contrast-enhanced abdominal CT scan is the best test to diagnose an AAA and guide treatment options.
Only 10–25% of patients survive rupture due to large pre- and post-operative mortality. Annual mortality from ruptured aneurysms in the United States is about 15,000. Most are due to abdominal aneurysms, with thoracic and thoracoabdominal aneurysms making up 1% to 4% of the total.
An aortic aneurysm can rupture from wall weakness. Aortic rupture is a surgical emergency, and has a high mortality even with prompt treatment.
- Coronary artery disease
- Elevated C-reactive protein
- Tobacco use
- Peripheral vascular disease
- Marfan syndrome
- Ehlers-Danlos type IV
- Bicuspid Aortic Valve
An aortic aneurysm can occur as a result of trauma, infection, or, most commonly, from an intrinsic abnormality in the elastin and collagen components of the aortic wall. While definite genetic abnormalities were identified in true genetic syndromes (Marfan, Elher-Danlos and others) associated with aortic aneurysms, both thoracic and abdominal aortic aneurysms demonstrate a strong genetic component in their aetiology.
The risk of aneurysm enlargement may be diminished with attention to the patient's blood pressure, smoking and cholesterol levels. 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 stabilizing properties.
Screening for an aortic aneurysm so that it may be detected and treated prior to rupture is the best way to reduce the overall mortality of the disease. The most cost-efficient screening test is an abdominal aortic ultrasound study. Noting the results of several large, population-based screening trials, the US Centers for Medicare and Medicaid Services (CMS) now provides payment for one ultrasound study in male or female smokers aged 65 years or older ("SAAAVE Act").
Surgery (open or endovascular) is the definite treatment of an aortic aneurysm. Medical therapy is typically reserved for smaller aneurysms or for elderly, frail patients where the risks of surgical repair exceed the risks of non-operative therapy (observation alone).
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.
The medical management of patients with aortic aneurysms, reserved for smaller aneurysms or frail patients, involves cessation of smoking, blood pressure control, use of statins and occasionally beta blockers. Ultrasound studies are obtained on a regular basis (i.e. every six or 12 months) to follow the size of the aneurysm.
Decisions about repairing an aortic aneurysm are based on the balance between the risk of aneurysm rupture without treatment versus the risks of the treatment itself. For example, a small aneurysm in an elderly patient with severe cardiovascular disease would not be repaired. The chance of the small aneurysm rupturing is overshadowed by the risk of cardiac complications from the procedure to repair the aneurysm.
The risk of the repair procedure is two-fold. First, one must consider the risk of problems occurring during and immediately after the procedure itself ("peri-procedural" complications). Second, however, one must also take the effectiveness of the procedure into account. Does the procedure effectively protect the patient from aneurysm rupture over the long-term? And, is the procedure durable so that secondary procedures, each with their own attendant risks, are not necessary over the life of the patient? These issues attain importance and should be considered when making a choice between different treatment options. A less invasive procedure (such as endovascular aneurysm repair) may be associated with fewer short-term risks to the patient (fewer peri-procedural complications) but secondary procedures may be necessary over long-term follow-up.
The definitive treatment for an aortic aneurysm may be surgical or endovascular repair. The determination of surgical intervention is complex and determined on a per-case basis. Risk of aneurysm rupture is weighed against procedural risk. The diameter of the aneurysm, its rate of growth, the presence or absence of Marfan Syndrome, Ehlers–Danlos Syndrome or similar connective tissue disorders, and other co-morbidities are all important factors in the overall treatment.
A rapidly expanding aneurysm should under normal circumstances be operated on as soon as feasible, as it has a greater chance of rupture. Slowly expanding aortic aneurysms may be followed by routine diagnostic testing (i.e.: CT scan or ultrasound imaging).
For abdominal aneurysms, the current treatment guidelines for abdominal aortic aneurysms suggest elective surgical repair when the diameter of the aneurysm is greater than 5 cm (2 in). However, recent data on patients aged 60–76 suggest medical management for abdominal aneurysms with a diameter of less than 5.5 cm (2 in).
Open surgery typically involves exposure of the dilated portion of the aorta and insertion of a synthetic (Dacron or Gore-Tex) graft (tube). Once the graft is sewn into the proximal (toward the patient's head) and distal (toward the patient's foot) portions of the aorta, the aneurysmal sac is closed around the graft. Alternatively, the anastomosis can be carried out with expandable devices, a simpler and quicker procedure 
The aorta and its branching arteries are cross-clamped during open surgery. This can lead to inadequate blood supply to the spinal cord, resulting in paraplegia, when repairing thoracic aneurysms. Cerebrospinal fluid drainage, when performed in experienced centers, reduces the risk of ischemic spinal cord injury by increasing the perfusion pressure to the spinal cord.
In the recent years, the endovascular treatment of aortic aneurysms has emerged as a minimally invasive alternative to open surgery repair. The first successful endovascular exclusion of an aneurysm took place in Argentina by Juan Parodi in 1991. The endovascular treatment of aortic aneurysms involves the placement of an endo-vascular stent through small incisions at the top of each leg 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 not only in individuals with comorbid conditions that make them high risk patients for open surgery, but also now in lower risk individuals.
There have also been many reports concerning the endovascular treatment of ruptured AAA, which are usually treated with an open surgical repair due to the time constraints and the time it takes to obtain imaging studies and prepare the patient for an endovascular repair. Mid-term results have been quite promising. However, due to the time frame of the emerging, the long term benefit of the EVAR procedure against open surgery has not yet been identified.
In spite of aneurysms having been treated by endovascular techniques in virtually all aortic segments, better than open aortic repair results were statistically documented only in uncomplicated, elective descending thoracic and infrarenal aorta. Moreover recent USA Nationwide Inpatient Sample data 2006–2007 review of isolated descending thoracic aorta aneurysm cases showed that only 23% (2,563/11,669) of ideal candidate (uncomplicated, elective descending aortic aneurysms) underwent to TEVAR, the remaining 77% (9,106/11,669) still underwent open surgical repair. Although results were better with TEVAR than with OAR it is clear that still the vast majority of thoracic aortic aneurysms is treated by standard open repair.
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