Chapter 60: Aneurysmal Disease

An aneurysm is dilation of the arterial wall to >1.5 times its normal diameter. Aneurysms have been classically distinguished as true aneurysms, pseudoaneurysms, and mycotic aneurysms. The wall of a true aneurysm involves of all layers of the vessel. Risk factors for these include connective tissue disorders, familial history of aneurysm, and atherosclerotic risk factors (i.e., age, smoking, hypertension, and hyperlipidemia). A progressive decrease in elastin, collagen, and fibrolamellar units results in thinning of the media of the vascular wall and a decrease in its tensile strength. In aortic true aneurysm, the dilatation and increased wall force are intertwined, creating more dilatation (Laplace law: wall tension = pressure × radius). The rate of aneurysmal dilatation is variable and predictable, with larger aneurysms expanding more quickly and changing a mean 0.25 to 0.5 cm per year. However, abrupt expansion occurs and is not predictable, with larger aneurysm more likely to rupture. Rupture is catastrophic, occurring once the stress on the vessel wall exceeds its tensile strength.

The wall of a pseudoaneurysm consists partly of the vessel wall and partly of fibrous or other surrounding tissue. A pseudoaneurysm can develop at the site of previous vessel catheterization and at anastomoses from prior vascular reconstruction, trauma, or infection.¹ Small pseudoaneurysms may eventually spontaneously thrombose.

A mycotic aneurysm develops as a result of infection in the vessel wall, often in an immunocompromised patient. The source can be direct extension from a neighboring infection or embolization from valvular endocarditis.

Peripheral and visceral aneurysms are less frequent but an important subset of arterial aneurysmal disease. Popliteal artery aneurysms are the most common peripheral aneurysm; they often co-exist with contralateral popliteal aneurysms or abdominal aortic aneurysms.² Aneurysms of the femoral artery are uncommon and often accompany aneurysmal disease at other sites. Visceral artery aneurysms may occur anywhere but are most common in the renal, splenic, and hepatic arteries. Most visceral aneurysms remain silent and undetected until a complication such as rupture occurs. All but splenic artery aneurysms are more common in elderly men. Complications of aneurysms include rupture, which has an 80% mortality rate,³ and thrombosis, creating ischemia in the perfused organ.^4,5

Clinical signs and symptoms can be nonspecific; often, the symptoms are driven by location, the pressure exerted upon neighboring structures, or the signs of peripheral embolization from an intramural thrombus. Visceral aneurysms are often detected after an abdominal CT scan for abdominal or flank complaints; similarly, lower extremity aneurysms are often detected during an extremity Doppler US examination in a search for deep venous thrombosis. Once rupture occurs in any truncal aneurysm, hemorrhagic shock develops and mortality is high without prompt surgical intervention.

An abdominal aortic aneurysm is defined as an aorta ≥3.0 cm in diameter; repair is considered for an aneurysm ≥5.0 cm in diameter. Patients with an abdominal aortic aneurysm often (18%) have a first-degree relative with an aortic aneurysm, compared with <3% of those without aneurysm. Most patients are >60 years old, and males have an increased risk of the disease. Patients with aneurysms involving other major arteries and those with peripheral arterial disease are also at increased risk for aortic aneurysmal disease. The risk increases with the number of years of smoking and decreases with the number of years since quitting smoking.⁶ As smoking becomes less prevalent in the United States, abdominal aortic aneurysm deaths have decreased.⁷

CLINICAL FEATURES

Symptomatic abdominal aortic aneurysms may present with a variety of signs or symptoms that can mimic other primary diagnoses: syncope; flank, back, or abdominal pain; GI bleeding from an aortoduodenal fistula; extremity ischemia from embolization of a thrombus in the aneurysm; shock; or sudden death. Sudden death most commonly occurs from intraperitoneal rupture of the aneurysm, which leads to massive, rapid blood loss. Syncope without warning symptoms followed by severe abdominal or back pain suggests rupture of an abdominal aortic or visceral aneurysm with some temporary containment. Syncope is caused by rapid blood loss and a lack of cerebral perfusion. Patients may regain consciousness, but irreversible hemorrhagic shock follows without prompt diagnosis and intervention.

Back or abdominal pain is the most common presenting symptom with aortic aneurysm or rupture. The pain is classically severe and abrupt in onset, with about half of patients describing a ripping or tearing pain. Syncope occurs in about 10%. Many patients present with nonclassic sites of pain: flank, groin, isolated quadrants of the abdomen, and hip. Other common symptoms exist, such as nausea, vomiting, bladder pain, hip pain, or tenesmus.

DIAGNOSIS

Physical examination has only a moderate ability to detect a large abdominal aortic aneurysm. The sensitivity of abdominal palpation increases with aortic aneurysm diameter, ranging from 29% for a diameter of 3.0 to 3.9 cm to 50% for a diameter of 4.0 to 4.9 cm and 76% for a diameter of ≥5.0 cm.⁸ Tenderness to palpation of an aneurysm is commonly interpreted as a sign of aneurysmal expansion or rupture. However, a lack of tenderness does not indicate an intact aorta. Examination is difficult in the obese and the very thin.

The differential diagnoses include the causes of syncope, abdominal pain, chest pain, back pain, and shock. When seeing patient with abrupt back pain with syncope or shock, consider aortic aneurysm rupture. However, other cardiac, abdominal, and retroperitoneal diseases may be the cause, including renal disorders, hepatobiliary disorders, and pancreatic disease. If symptoms are insidious, it is possible that some patients may appear well enough and receive benign diagnoses, such as musculoskeletal back pain, and are discharged from the ED.

Diagnosis is confounded by coexisting pathology. Coronary artery disease and chronic lung disease are often present, and signs and symptoms of these disorders may distract the physician from the diagnosis of aneurysmal disease. This is especially true in patients without severe pain or with findings that seem congruent with another cause (e.g., ECG changes or dyspnea).

External signs of acute rupture are rare and include periumbilical ecchymosis (Cullen sign) or flank ecchymosis (Grey Turner sign). Retroperitoneal blood may dissect into the perineum or groin, causing scrotal or vulvar hematomas, or inguinal masses. Retroperitoneal blood may irritate the psoas muscle, triggering an "iliopsoas sign" (pain upon extension of the hip, typically with the patient lying on the opposite side). Blood may compress the femoral nerve and present as a neuropathy. The presence or rupture of an abdominal aortic aneurysm typically does not alter femoral arterial pulsations.⁹

Think of aortoenteric fistulas in patients with unexplained or high-volume upper or lower GI bleeding, especially in patients without liver disease. A history of aortic graft placement increases the risk of fistula. Fistulas most frequently involve the duodenum, with hematemesis, melenemesis, melena, or hematochezia. While massive, life-threatening bleeding is common, mild sentinel bleeding may be the first sign. Aortic aneurysms also may erode into the venous vasculature and form aortovenous fistulas, which cause high-output cardiac failure, decreased arterial blood flow distal to the fistula, and increased central venous volume.

Contained chronic abdominal aortic aneurysmal ruptures are not common. A retroperitoneal rupture may cause enough fibrosis to limit blood loss, and the patient may look well. The inflammatory response commonly causes pain, with pain continuing for an extended interval, clouding the diagnosis.

Imaging

Imaging performed away from the bedside can delay emergency consultation and operative repair, so consult a surgeon early and before any transport for imaging when a symptomatic aneurysm is suspected.

Radiologic evaluation may include plain radiography (Figure 60-1), US (Figure 60-2), CT scanning (Figure 60-3), or MRI. Plain abdominal films may show a calcified and bulging aortic contour, implying the presence of an aneurysm (Figure 60-1). Approximately 65% of patients with symptomatic aortic aneurysmal disease have a calcified aorta, often better seen on a lateral view. An anteroposterior projection may show an arch of calcification, most commonly on the patient's left. Rarely, a chronic aneurysm may erode into a vertebral body and be seen on plain film. Plain film radiographs do not exclude the presence of abdominal aortic aneurysm or detect rupture and can be omitted in most patients.

Bedside US (Figure 60-2) is ideal for initial screening and for patients with any hemodynamic compromise. Emergency US is noninvasive, easily deployed, and does not entail removal of the patient from the resuscitation area.¹⁰ A technically adequate US study has >90% sensitivity for demonstrating the presence of an aneurysm and measuring its diameter.¹⁰ Obesity, bowel gas, and abdominal tenderness may make the study difficult to perform. Measure aneurysms from the outside margin of one wall to the outside margin of the opposite wall in both the transverse (Figure 60-4) and longitudinal (Figure 60-5) planes. Identifying the superior mesenteric artery (Figure 60-6) allows distinguishing the aorta from the vena cava. An aortic diameter <3.0 cm excludes acute aneurysmal disease.

CT scanning with IV contrast (Figure 60-3) best detects the anatomic details of the aneurysm and associated hemorrhage. Scan all stable patients with suspected abdominal aneurysmal disease or rupture. For those who cannot have IV contrast, unenhanced CT can reveal aneurysm size and retroperitoneal hemorrhage.

ED interventions are listed in Table 60-1.

All asymptomatic aortic aneurysms should be referred for follow-up. Abdominal aortic aneurysms ≥5 cm in diameter are at an increased risk of rupture (size is measured from outer wall to outer wall) and require prompt (days) follow-up. Aneurysms of 3 to 5 cm are less likely to rupture and can be followed by their primary care physicians or surgeons. The management of patients with small, asymptomatic aneurysms (including the timing of surgery) varies. Symptomatic aneurysms of any size are considered emergent.

All symptomatic aortic aneurysms require emergency surgical consultation or transfer to an institution capable of performing emergency repair. If at a site without appropriate surgical ability, initiate patient resuscitation and arrange for immediate transfer to a medical center that can provide emergency repair. Outcomes are better if prompt transfer occurs rather than local diagnostics (aside from bedside US).^11,12 Immediate transfer with providers able to recognize and treat shock (having fluid, blood, and blood products available) is the best option for patients in unstable condition.

In the ED, detection and arranging rapid care for hemorrhage control are key. Consult a surgeon early while evaluating any patient with the triad of abdominal and/or back pain, a pulsatile abdominal mass, and hypotension¹³; however, this triad occurs in only one third of patients with ruptured abdominal aortic aneurysm.⁸ Never delay consultation for imaging if hypotension or acute end-organ perfusion deficit is evident; often, bedside US can aid in quick tentative diagnosis.¹³

Any ruptured aortic aneurysm requires prompt operative repair. Use imaging only in those fully compensated or unlikely to have a ruptured abdominal aortic aneurysm. Standard resuscitative actions include insertion of two large-bore IV catheters, initiation of cardiac monitoring, and supplemental oxygen. Vigorous fluid resuscitation may be harmful; there are limited data, but animal research and anecdote support limiting resuscitation to a target of 90 mm Hg blood pressure and intact mentation until surgical control occurs.¹⁵ Perioperative administration of β-blockers in nonruptured aneurysms reduces dysrhythmias and myocardial ischemia but does not appear to affect the rate of myocardial infarction, mortality, or length of hospitalization.¹³ When used, esmolol (a short-acting β-blocker) is a common choice.

Endovascular techniques for the repair of ruptured abdominal aortic aneurysm are a feasible alternative to an open repair.¹⁶ This intervention requires a skilled provider and appropriate facilities and team members.

Refer any patient with asymptomatic aortic abdominal aneurysms to a vascular surgeon and a primary care provider, the latter for blood pressure control.¹⁷ Repairing aortic abdominal aneurysms smaller than 5.5 cm does not improve survival in men,¹⁷ but may be indicated in women.¹⁴

Thoracic aortic aneurysms may compress or erode into adjacent structures. Presenting symptoms include esophageal, tracheal, bronchial, or even neurologic complaints. A thoracic aneurysm that erodes into an adjacent structure is generally immediately fatal unless in the presence of rapid hemodynamic resuscitation. Refer any asymptomatic thoracic aortic aneurysm patient to a surgeon and primary care provider for management, including blood pressure control. Repair may involve open or endovascular methods, with controversy over the best long-term outcomes between these approaches.¹⁸

Aneurysms of arteries other than the aorta cause symptoms by expansion or rupture. Table 60-2 lists the risk factors, clinical presentation, and management of nonaortic large-artery aneurysms. Aneurysms of peripheral arteries, such as the popliteal, subclavian, or femoral, may present with limb-threatening complications, including rupture, thrombosis, and peripheral embolization. Visceral artery aneurysms remain silent until a complication occurs. Complications include renovascular hypertension, renal artery thrombosis, organ infarction from distal embolization, arteriovenous fistula formation, and rupture.^19,20 Consider visceral artery aneurysms in the differential diagnosis of a patient with sudden acute abdominal pain and evidence for intraperitoneal hemorrhage.^4,5,13,21

A popliteal aneurysm is a localized dilation of the popliteal artery of >2 cm or >150% of the normal arterial caliber. Symptoms include discomfort behind the knee, leg swelling with or without deep venous thrombosis, or claudication. Rupture is rare. Sudden acute limb ischemia caused by thrombosis or embolization from the aneurysm is the most serious common complication.² On physical examination, a firm mass or a palpable pulsatile mass is evident in the popliteal fossa. Confirm the diagnosis with arterial US, and assess both extremities since popliteal aneurysms can be bilateral.

Femoral or iliac artery aneurysms present as a pulsatile mass in the groin or upper thigh, scrotal hematoma, or acute limb ischemia. Iliac artery aneurysms are notoriously difficult to suspect clinically because the iliac artery cannot be examined directly, and symptoms suggest urologic, bowel, or groin disorders.

Hepatic artery aneurysms result from atherosclerosis or trauma and present as acute hemorrhagic shock with intraperitoneal or retroperitoneal rupture. Quincke's triad (jaundice, biliary colic, and upper GI bleeding) is seen when hemobilia from a leaking hepatic artery aneurysm occurs.

Splenic artery aneurysms present with left upper quadrant pain, undifferentiated shock, or intra-abdominal hemorrhage. A rupture of the splenic artery has a poor prognosis because of its intraperitoneal location and nondescript presentation; be wary of these in the third trimester of pregnancy.²¹

Symptomatic subclavian and innominate artery aneurysms can lead to limb ischemia. When evaluating a patient with upper extremity pain, weakness, pallor, or nondermatome sensory changes, think of this as a possible cause.

Anastomotic aneurysms may occur in the aortic, iliac, or femoral arteries. These aneurysms cause catastrophic bleeding if they rupture; however, they may present with smaller sentinel hemorrhages noted as pain or transient hypotension. Anastomotic aneurysms may erode into the adjacent intestine and form an aortoenteric fistula. Severe lower GI bleeding in a patient with a history of abdominal aortic aneurysm repair is a classic presentation of this event.

Doppler US is the initial noninvasive diagnostic study for peripheral aneurysmal disease of the femoral, popliteal, and subclavian artery. If ischemia and thrombosis exist, emergent arteriography is usually performed for both diagnosis and potential treatment.

Symptomatic peripheral artery aneurysms require rapid diagnosis and consultation, especially in light of the potential for rupture, thrombosis, and limb ischemia (Table 60-2). For patients with clinical extremity ischemia, consult immediately with a vascular surgeon to expedite repair and limb salvage. Asymptomatic peripheral aneurysms are managed by a vascular consultant as an outpatient.

The 2011 American Heart Association guidelines are available at http://circ.ahajournals.org/content/124/18/2020.