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Aneurysms are abnormal dilations of arteries caused by weakening of the arterial wall. Common causes include hypertension, atherosclerosis, infection, trauma, and hereditary or acquired connective tissue disorders. Aneurysms are usually asymptomatic but can cause pain and lead to ischemia, thromboembolism, spontaneous dissection, and rupture, which may be fatal. Diagnosis is by imaging tests (eg, ultrasonography, CT angiography, magnetic resonance angiography, aortography). Treatment of unruptured aneurysms is with risk factor modification (eg, strict BP control) plus surveillance imaging or with open or endovascular stent-graft surgery, depending on size and location of the aneurysm and presence of symptoms. Treatment of ruptured aneurysms is immediate repair by either an open surgical synthetic graft or an endovascular stent-graft.
Aneurysms, defined as a ≥ 50% increase in arterial diameter compared with normal segments, result from localized weakening of an arterial wall. True aneurysms involve all 3 layers of the artery (intima, media, and adventitia). A pseudoaneurysm (false aneurysm) is a communication between the arterial lumen and overlying connective tissue resulting from arterial rupture; a blood-filled cavity forms outside the vessel wall and seals the leak as it thromboses. Aneurysms are classified as fusiform (circumferential widening of the artery) or saccular (localized outpouchings of the artery wall). Thrombi that develop in layers (laminated thrombi) may line the walls of either type and are a sign that blood flow beyond the aneurysm is normal or near normal.
Aneurysms may occur in any artery. Abdominal and thoracic aortic aneurysms are most common and significant; aneurysms of the major branches (subclavian and splanchnic arteries) are much less common. Aneurysms of the cerebrovascular system are discussed in see Stroke (CVA): Vascular Lesions in the Brain .
Abdominal Aortic Aneurysms (AAA)
Abdominal aortic aneurysms (AAAs) account for three fourths of aortic aneurysms and affect 0.5 to 3.2% of the population. Prevalence is 3 times greater in men. AAAs typically begin below the renal arteries but may include renal arterial ostia; about 50% involve the iliac arteries. Generally, aortic diameter ≥ 3 cm constitutes an AAA. Most AAAs are fusiform; some are saccular. Many are lined with laminated thrombi. AAAs involve all layers of the aorta and do not involve dissection; however, a thoracic aortic dissection may extend to the distal abdominal aorta.
Etiology
The most common cause is weakening of the arterial wall, usually associated with atherosclerosis. Other causes include trauma, vasculitis, cystic medial necrosis, and postsurgical anastomotic disruption. Uncommonly, syphilis and localized bacterial or fungal infection, typically due to sepsis or infective endocarditis, weaken the arterial wall and cause infected (mycotic) aneurysms.
Smoking is the strongest risk factor. Other risk factors include hypertension, older age (peak incidence at age 70 to 80), family history (in 15 to 25%), race (more common in whites than in blacks), and male sex.
Symptoms and Signs
Most AAAs are asymptomatic; symptoms and signs, when they do occur, may not be specific. As AAAs expand, they may cause pain, which is steady, deep, boring, visceral, and felt most prominently in the lumbosacral region; patients may be aware of an abnormally prominent abdominal pulsation. Rapidly enlarging aneurysms that are about to rupture are frequently tender, but most aneurysms grow slowly without symptoms.
The aneurysm may or may not be palpable as a pulsatile mass, depending on its size and patient habitus. The probability that a patient with a pulsatile palpable mass has an aneurysm > 3 cm is about 40% (positive predictive value). A systolic bruit may be audible over the aneurysm.
If an AAA ruptures, patients who do not die immediately typically present with abdominal or back pain, hypotension, and tachycardia. They may have a history of recent upper abdominal trauma, often minimal, or isometric straining (eg, lifting a heavy object).
Patients with an occult AAA sometimes present with symptoms of complications (eg, extremity pain due to embolization of mural thrombi) or of the cause (eg, fever, malaise, or weight loss due to infection or vasculitis). Uncommonly, large AAAs cause disseminated intravascular coagulation, perhaps because large areas of abnormal endothelial surface trigger rapid thrombosis and consumption of coagulation factors.
Diagnosis
Most AAAs are diagnosed incidentally when they are detected during physical examination or when abdominal ultrasonography, CT, or MRI is done for other reasons. An AAA should be considered in elderly patients who present with acute abdominal or back pain whether a palpable pulsatile mass is present or not.
When symptoms or physical examination findings suggest AAA, abdominal ultrasonography or CT is usually the test of choice. Symptomatic patients should have immediate testing to make the diagnosis before catastrophic rupture. For hemodynamically unstable patients with presumed rupture, ultrasonography provides bedside results more rapidly, but intestinal gas and distention may limit its accuracy. Laboratory tests, including CBC, electrolytes, BUN, creatinine, PT, PTT, blood type and cross-match, are done in preparation for possible surgery.
If rupture is not suspected, CT angiography (CTA) or magnetic resonance angiography (MRA) can more precisely characterize aneurysm size and anatomy. If thrombi line the aneurysm wall, CTA may underestimate true size; noncontrast CT may provide a more accurate estimate. Aortography is essential if renal artery or aortoiliac disease is suspected or if correction with endovascular stent-grafts (endografts) is being considered.
Plain abdominal x-rays are neither sensitive nor specific; however, if obtained for other purposes, aortic calcification may outline the aneurysm wall. If a mycotic aneurysm is suspected, bacterial and fungal blood cultures should be done.
Treatment
Some AAAs enlarge at a steady rate (2 to 3 mm/yr), some enlarge exponentially, and, for unknown reasons, about 20% remain the same size indefinitely. The need for treatment is related to size, which is linked to risk of rupture (see Table 1: Diseases of the Aorta and Its Branches: Abdominal Aortic Aneurysm Size and Rupture Risk* ).
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Table 1
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PrintOpen table  |
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| Abdominal Aortic Aneurysm Size and Rupture Risk* |
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AAA Diameter (cm)
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Rupture Risk (%/yr)
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< 4
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0
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4–4.9
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1%
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5–5.9*
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5–10%
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6–6.9
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10–20%
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7–7.9
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20–40%
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> 8
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30–50%
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*Elective surgical repair should be considered for aneurysms > 5.0–5.5 cm.
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Ruptured AAAs require immediate open surgery or endovascular stent grafting. Without treatment, mortality rate approaches 100%. With open surgical treatment, mortality rate is about 50%; mortality with endovascular stent grafting is generally lower (20 to 30%). The mortality remains high because many patients have coexisting coronary, cerebrovascular, and peripheral atherosclerosis. Patients who present in hemorrhagic shock require fluid resuscitation (see Shock and Fluid Resuscitation: Fluids) and blood transfusions, but mean arterial pressure should not be elevated to > 70 to 80 mm Hg because bleeding may increase. Preoperative control of hypertension is important.
Elective surgical repair is recommended for aneurysms > 5 to 5.5 cm (when risk of rupture increases to > 5 to 10%/yr), unless coexisting medical conditions contraindicate surgery. Additional indications for elective surgery include increase in aneurysm size by > 0.5 cm within 6 mo regardless of size, chronic abdominal pain, thromboembolic complications, and an iliac or femoral artery aneurysm that causes lower-limb ischemia. Before elective repair, clinical recognition of coronary artery disease (CAD) is essential (see Table 1: Cardiovascular Tests and Procedures: Tests for Assessing Cardiac Anatomy and Function) because many patients with an AAA have generalized atherosclerosis and surgical repair poses a major risk of cardiovascular events. Aggressive medical treatment and risk factor control are essential, and revascularization should be considered only in patients with unstable CAD. Routine preoperative coronary angioplasty or bypass surgery has not been shown to be necessary in most patients who can be prepared with good medical management before aneurysm repair.
Surgical repair consists of replacing the aneurysmal portion of the abdominal aorta with a synthetic graft. If the iliac arteries are involved, the graft must be extended to include them. If the aneurysm extends above the renal arteries, the renal arteries must be reimplanted into the graft, or bypass grafts must be created.
Placement of an endovascular stent-graft within the aneurysmal lumen via the femoral artery is a less invasive alternative and is indicated when risk of perioperative complications is high. This procedure excludes the aneurysm from systemic blood flow and reduces risk of rupture. The aneurysm eventually thromboses, and 50% of aneurysms decrease in diameter. Short-term results are good, but long-term results are unknown. Complications include angulation, kinking, thrombosis, migration of the stent-graft, and endoleak (persistent flow of blood into the aneurysm sac after endovascular stent-graft placement). Thus, follow-ups must be more frequent after endovascular stent-graft placement than after a traditional repair. If no complications occur, imaging tests are recommended at 1 mo, 6 mo, 12 mo, and every year thereafter. Complex anatomy (eg, short aneurysm neck below renal arteries, severe arterial tortuosity) makes endovascular stent grafting difficult in 30 to 40% of patients.
Repair of aneurysms < 5 cm does not appear to improve survival. These aneurysms should be monitored with ultrasonography every 6 to 12 mo for expansion that warrants treatment. Control of atherosclerotic risk factors, especially smoking cessation and use of antihypertensives as appropriate, is important. If a small or moderate-sized aneurysm becomes > 5.5 cm and if risk of perioperative complications is lower than estimated risk of rupture, AAA repair is indicated; risk of rupture vs that of perioperative complications should be discussed frankly with the patient.
Treatment of a mycotic aneurysm consists of vigorous antimicrobial therapy directed at the pathogen, followed by excision of the aneurysm. Early diagnosis and treatment improve outcome.
Thoracic Aortic Aneurysms
Thoracic aortic aneurysms (TAAs) account for one fourth of aortic aneurysms. Men and women are affected equally. About 40% of TAAs occur in the ascending thoracic aorta (between the aortic valve and brachiocephalic, or innominate, artery), 10% occur in the aortic arch (including the brachiocephalic, carotid, and subclavian arteries), 35% occur in the descending thoracic aorta (distal to the left subclavian artery), and 15% occur in the upper abdomen (as thoracoabdominal aneurysms).
Etiology
Most TAAs result from atherosclerosis. Risk factors for both include prolonged hypertension, dyslipidemia, and smoking; additional risk factors for TAAs include presence of aneurysms elsewhere and older age (peak incidence at age 65 to 70).
Congenital connective tissue disorders (eg, Marfan syndrome, Ehlers-Danlos syndrome) cause cystic medial necrosis, a degenerative change that leads to TAAs complicated by aortic dissection (see Diseases of the Aorta and Its Branches: Aortic Dissection) and by widening of the proximal aorta and aortic valve (annuloaortic ectasia), which causes aortic regurgitation. Marfan syndrome causes 50% of cases of annuloaortic ectasia, but cystic medial necrosis and its complications can occur in young people even if no congenital connective tissue disorder is present.
Infected (mycotic) TAAs result from hematogenous spread of systemic or local infections (eg, sepsis, pneumonia), lymphangitic spread (eg, in TB), or direct extension (eg, in osteomyelitis or pericarditis). Bacterial endocarditis and tertiary syphilis are uncommon causes. TAAs occur in some connective tissue disorders (eg, temporal arteritis, Takayasu's arteritis, Wegener's granulomatosis).
Blunt chest trauma causes pseudoaneurysms (extramural hematomas due to blood that has leaked through the torn aortic wall).
TAAs may dissect, compress or erode into adjacent structures, lead to thromboembolism, leak, or rupture.
Symptoms and Signs
Most TAAs are asymptomatic until complications (eg, thromboembolism, rupture, aortic regurgitation, dissection) develop. However, compression of adjacent structures can cause chest or back pain, cough, wheezing, dysphagia, hoarseness (due to left recurrent laryngeal or vagus nerve compression), chest pain (due to coronary artery compression), and superior vena cava syndrome. Erosion of aneurysms into the lungs causes hemoptysis or pneumonitis; erosion into the esophagus (aortoesophageal fistula) causes massive hematemesis. Dissection manifests with tearing pain, often radiating to the back. Thromboembolism may cause stroke, abdominal pain (due to mesenteric embolism), or extremity pain. Patients who do not immediately die of a ruptured TAA present with severe chest or back pain and hypotension or shock; exsanguination most commonly occurs into the pleural or pericardial space.
Additional signs include Horner syndrome due to compression of sympathetic ganglia, palpable downward pull of the trachea with each cardiac contraction (tracheal tug), and tracheal deviation. Visible or palpable chest wall pulsations, occasionally more prominent than the left ventricular apical impulse, are unusual but may occur.
Syphilitic aneurysms of the aortic root classically lead to aortic regurgitation and inflammatory stenosis of the coronary artery ostia, which may manifest as chest pain due to myocardial ischemia. Syphilitic aneurysms do not dissect.
Diagnosis
TAAs are usually first suspected when a chest x-ray incidentally shows a widened mediastinum or enlargement of the aortic knob. These findings or symptoms and signs suggesting an aneurysm should be followed up with a 3-dimensional imaging test. CTA can delineate aneurysm size and proximal or distant extent, detect leakage, and identify coincident pathology. MRA may provide similar detail. TEE can delineate size and extent and detect leakage of aneurysms of the ascending but not descending aorta; TEE is especially useful for detecting aortic dissection. Contrast angiography provides the best image of the arterial lumen but no information on extraluminal structures, is invasive, and has a significant risk of renal and extremity atheroembolism and contrast nephropathy. Choice of imaging test is based on availability and local experience; however, if rupture is suspected, TEE or CTA, depending on availability, is done immediately.
Aortic root dilation or unexplained ascending aorta aneurysms warrant serologic testing for syphilis. If a mycotic aneurysm is suspected, bacterial and fungal blood cultures are done.
Prognosis
TAAs enlarge an average of 3 to 5 mm/yr; risk factors for rapid enlargement include larger size of aneurysm, location in the descending aorta, and presence of mural thrombi. Median diameter at aneurysm rupture is 6 cm for ascending aneurysms and 7 cm for descending aneurysms, but rupture of smaller aneurysms may occur in patients with Marfan syndrome. Survival rate of patients with untreated large TAAs is 65% at 1 yr and 20% at 5 yr.
Treatment
Treatment is endovascular stent grafting when anatomically possible and open surgical repair for more complex aneurysms. Immediate control of hypertension is essential.
Ruptured TAAs, if untreated, are universally fatal; they require immediate intervention, as do leaking aneurysms and those that cause acute dissection or acute valvular regurgitation. Surgery involves a median sternotomy (for ascending and aortic arch aneurysms) or left thoracotomy (for descending and thoracoabdominal aneurysms) and subsequent excision of the aneurysm and replacement with a synthetic graft. Transcatheter-placed endovascular stent-grafts (endografts) for descending TAAs are being used more frequently as a less invasive alternative to open surgery. With emergency surgery, 1-mo mortality rate is about 40 to 50%. In patients who survive, incidence of serious complications (eg, renal failure, respiratory failure, severe neurologic damage) is high.
Elective surgery is indicated for large aneurysms (diameter > 5 to 6 cm in the ascending aorta, > 6 to 7 cm in the descending aorta, and, for patients with Marfan syndrome, > 5 cm in any location) and also for those that rapidly enlarge (> 1 cm/yr). Elective surgery is also indicated for symptomatic, traumatic, or syphilitic aneurysms. For syphilitic aneurysms, benzathine penicillin 2.4 million units once/wk IM is given for 3 wk afterward. For patients allergic to penicillin, tetracycline or erythromycin 500 mg po qid for 30 days is acceptable.
Although surgical repair of an intact TAA improves outcome, mortality rate may still exceed 5 to 10% at 30 days and is 40 to 50% at 10 yr. Risk of death increases greatly if aneurysms are complicated (eg, in the aortic arch or thoracoabdominal aorta) or if patients have CAD, are older, are symptomatic, or have preexisting renal insufficiency. Perioperative complications (eg, stroke, spinal injury, renal failure) occur in about 10 to 20%.
Asymptomatic aneurysms that do not meet criteria for elective surgical or endovascular repair are treated with aggressive BP control using a β-blocker and other antihypertensives if necessary. Smoking cessation is essential. Patients require frequent follow-ups to check for symptoms and serial CT every 6 to 12 mo.
Aortic Branch Aneurysms
Aneurysms may occur in any major aortic branch; such aneurysms are much less common than abdominal or thoracic aortic aneurysms. Risk factors include atherosclerosis, hypertension, cigarette smoking, and older age. Localized infection can cause mycotic aneurysms.
Subclavian artery aneurysms are sometimes associated with cervical ribs or thoracic outlet syndrome.
Splanchnic artery aneurysms are uncommon. About 60% occur in the splenic artery, 20% in the hepatic artery, and 5.5% in the superior mesenteric artery. Splenic artery aneurysms occur in more women than men (4:1). Causes include medial fibromuscular dysplasia, portal hypertension, multiple pregnancies, penetrating or blunt abdominal trauma, pancreatitis, and infection. Hepatic artery aneurysms occur in more men than women (2:1). They may result from previous abdominal trauma, illicit IV drug use, medial degeneration of the arterial wall, or periarterial inflammation. Renal artery aneurysms may dissect or rupture, causing acute occlusion (see Renovascular Disorders: Acute occlusion).
Symptoms and Signs
Symptoms vary. Subclavian aneurysms can cause local pain, a pulsating sensation, venous thrombosis or edema (due to compression of adjacent veins), distal ischemic symptoms, transient ischemic attacks, stroke, or hoarseness or impaired motor and sensory function (due to compression of the recurrent laryngeal nerve or brachial plexus). Superior mesenteric aneurysms may cause abdominal pain and ischemic colitis.
Regardless of location, mycotic or inflammatory aneurysms may cause local pain and sequelae of systemic infection (eg, fever, malaise, weight loss).
Diagnosis
Most aortic branch aneurysms are not diagnosed before rupture, although calcified asymptomatic or occult aneurysms may be seen on x-rays or other imaging tests done for other reasons. Ultrasonography or CT is typically used to detect or confirm aortic branch aneurysms. Angiography can be used as needed to evaluate distal symptoms thought to be due to the aneurysm or embolism.
Treatment
Treatment is surgical removal and replacement with a graft. Endovascular repair is an option for some patients. The decision to repair asymptomatic aneurysms is based on risk of rupture, extent and location of the aneurysm, and perioperative risk.
Surgery for subclavian artery aneurysms may involve removal of a cervical rib (if present) before repair and replacement.
For splanchnic aneurysms, risk of rupture and death is as high as 10% and is particularly high for women of childbearing age and for patients with hepatic aneurysms (> 35%). Elective repair of splanchnic aneurysms is therefore indicated for women of childbearing age, for symptomatic aneurysms in other age groups, and for hepatic aneurysms. For splenic aneurysms, repair may consist of ligation without arterial reconstruction or aneurysm exclusion and vascular reconstruction. Depending on location of the aneurysm, splenectomy may be necessary.
Treatment of mycotic aneurysms is aggressive antibiotic therapy directed at the specific pathogen. Generally, these aneurysms must also be surgically repaired.
Last full review/revision January 2008 by John W. Hallett, Jr., MD
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