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Emergency and Acute Medicine – Abdominal Aortic Aneurysm (AAA)
Overview and Definition
An abdominal aortic aneurysm is defined as a focal dilation of the abdominal aorta with an increase in diameter of at least 50%, most commonly exceeding 3 cm. Approximately 95% of aneurysms are located below the renal arteries. The majority remain clinically silent until rapid enlargement or rupture occurs. Rupture may extend into either the retroperitoneal or intraperitoneal space; intraperitoneal rupture is usually catastrophic and often immediately fatal. Average aneurysm growth is approximately 0.2–0.5 cm per year. Overall mortality following rupture approaches 90%, remaining high even among patients who reach the hospital and those who undergo emergency surgical repair.
Epidemiology and Geriatric Considerations
The risk of AAA increases significantly with age. It is present in 4–8% of individuals older than 65 years and is more common in men. Prevalence rises further in advanced age groups. Although less common in women, aneurysms in women rupture more frequently and at smaller diameters compared with men.
Etiology and Risk Factors
Major risk factors include male sex, age over 65 years, cigarette smoking, family history, atherosclerosis, hypertension, and diabetes mellitus. Inherited connective tissue disorders such as Ehlers–Danlos syndrome and Marfan syndrome also increase susceptibility. Less common causes include blunt abdominal trauma, congenital aneurysms, and infectious involvement of the aorta, including mycotic aneurysms associated with endocarditis.
Rupture risk is strongly related to aneurysm size and growth rate. Larger aneurysms have progressively higher annual rupture rates, and rapid expansion—greater than 0.5 cm within six months—signals a high risk of rupture. Women have up to a fourfold increased rupture risk compared with men for aneurysms of similar size.
Clinical Presentation
Most unruptured aneurysms are asymptomatic and discovered incidentally. When symptoms occur, patients may complain of abdominal, back, or flank pain that is vague, dull, constant, throbbing, or colicky. Pain may radiate to the chest, groin, thigh, inguinal region, or scrotum. Some patients experience lower extremity pain, syncope, or near-syncope.
Ruptured AAA may present with the classic triad of abdominal or back pain, hypotension, and a pulsatile abdominal mass, although all three findings are present in only a minority of cases. Additional findings include tachycardia, signs of shock, flank ecchymosis indicating retroperitoneal hemorrhage, abdominal tenderness, abdominal bruit, gastrointestinal bleeding, and diminished or asymmetric lower-extremity pulses. Complications include thromboembolism causing acute limb ischemia, microemboli resulting in “blue toe syndrome,” and aortoenteric fistula presenting with gastrointestinal hemorrhage.
Initial Assessment and Essential Workup
Evaluation is dictated by hemodynamic stability. Unstable patients require immediate bedside abdominal ultrasonography to rapidly identify an aneurysm, followed by urgent operative intervention without delay for further testing. Stable but symptomatic patients should undergo abdominal CT imaging to confirm the diagnosis, assess aneurysm size, and identify rupture location. Diagnostic studies must never delay definitive surgical management when rupture is suspected.
Diagnostic Tests and Interpretation
Laboratory evaluation includes complete blood count, renal function tests, coagulation studies, urinalysis, and immediate blood typing and cross-matching.
Plain abdominal or lumbar radiographs may show curvilinear calcification of the aortic wall or a paravertebral soft-tissue mass but cannot reliably detect rupture and should not be used to exclude the diagnosis.
Ultrasonography is highly sensitive and specific for detecting AAA prior to rupture and is the imaging modality of choice in unstable patients, though sensitivity decreases once rupture has occurred.
CT scanning provides accurate measurement of aneurysm diameter, identifies rupture location, and guides operative planning. CT angiography is required when endovascular repair is being considered.
Differential Diagnosis
The differential diagnosis includes aortic dissection, renal or biliary colic, pancreatitis, cholecystitis, appendicitis, bowel obstruction, perforated viscus, mesenteric ischemia, diverticulitis, gastrointestinal hemorrhage, myocardial infarction, sepsis, adrenal crisis, spinal cord compression, and other abdominal arterial aneurysms.
Prehospital and Emergency Department Management
Prehospital care focuses on rapid recognition, establishment of two large-bore intravenous lines, and expedited transport to a facility with surgical capability. Early notification allows preparation of the operating room, blood products, and vascular surgery consultation.
In the emergency department, management includes cardiac monitoring, cautious crystalloid infusion, and early blood transfusion. Excessive fluid resuscitation should be avoided, as it may increase bleeding before surgical control. Once symptomatic AAA is suspected, emergent vascular surgery consultation and definitive operative repair—open or endovascular—are mandatory.
Disposition and Follow-Up
All patients with symptomatic AAA require immediate surgical intervention and hospital admission. Asymptomatic patients may be discharged only with reliable outpatient vascular surgery follow-up.
Discharge Instructions and Safety Netting
Patients should be instructed to seek immediate medical attention for new or worsening pain in the abdomen, back, flank, or lower extremities, as well as dizziness or syncope.
Clinical Pearls and Pitfalls
AAA must be considered in any patient presenting with abdominal, back, or flank pain, particularly older adults and smokers. Symptomatic aneurysms represent true surgical emergencies, and definitive care should never be delayed for additional diagnostic studies. Hemodynamically unstable patients should not be sent for CT imaging.
Overview and Definition
An abdominal aortic aneurysm is defined as a focal dilation of the abdominal aorta with an increase in diameter of at least 50%, most commonly exceeding 3 cm. Approximately 95% of aneurysms are located below the renal arteries. The majority remain clinically silent until rapid enlargement or rupture occurs. Rupture may extend into either the retroperitoneal or intraperitoneal space; intraperitoneal rupture is usually catastrophic and often immediately fatal. Average aneurysm growth is approximately 0.2–0.5 cm per year. Overall mortality following rupture approaches 90%, remaining high even among patients who reach the hospital and those who undergo emergency surgical repair.
Epidemiology and Geriatric Considerations
The risk of AAA increases significantly with age. It is present in 4–8% of individuals older than 65 years and is more common in men. Prevalence rises further in advanced age groups. Although less common in women, aneurysms in women rupture more frequently and at smaller diameters compared with men.
Etiology and Risk Factors
Major risk factors include male sex, age over 65 years, cigarette smoking, family history, atherosclerosis, hypertension, and diabetes mellitus. Inherited connective tissue disorders such as Ehlers–Danlos syndrome and Marfan syndrome also increase susceptibility. Less common causes include blunt abdominal trauma, congenital aneurysms, and infectious involvement of the aorta, including mycotic aneurysms associated with endocarditis.
Rupture risk is strongly related to aneurysm size and growth rate. Larger aneurysms have progressively higher annual rupture rates, and rapid expansion—greater than 0.5 cm within six months—signals a high risk of rupture. Women have up to a fourfold increased rupture risk compared with men for aneurysms of similar size.
Clinical Presentation
Most unruptured aneurysms are asymptomatic and discovered incidentally. When symptoms occur, patients may complain of abdominal, back, or flank pain that is vague, dull, constant, throbbing, or colicky. Pain may radiate to the chest, groin, thigh, inguinal region, or scrotum. Some patients experience lower extremity pain, syncope, or near-syncope.
Ruptured AAA may present with the classic triad of abdominal or back pain, hypotension, and a pulsatile abdominal mass, although all three findings are present in only a minority of cases. Additional findings include tachycardia, signs of shock, flank ecchymosis indicating retroperitoneal hemorrhage, abdominal tenderness, abdominal bruit, gastrointestinal bleeding, and diminished or asymmetric lower-extremity pulses. Complications include thromboembolism causing acute limb ischemia, microemboli resulting in “blue toe syndrome,” and aortoenteric fistula presenting with gastrointestinal hemorrhage.
Initial Assessment and Essential Workup
Evaluation is dictated by hemodynamic stability. Unstable patients require immediate bedside abdominal ultrasonography to rapidly identify an aneurysm, followed by urgent operative intervention without delay for further testing. Stable but symptomatic patients should undergo abdominal CT imaging to confirm the diagnosis, assess aneurysm size, and identify rupture location. Diagnostic studies must never delay definitive surgical management when rupture is suspected.
Diagnostic Tests and Interpretation
Laboratory evaluation includes complete blood count, renal function tests, coagulation studies, urinalysis, and immediate blood typing and cross-matching.
Plain abdominal or lumbar radiographs may show curvilinear calcification of the aortic wall or a paravertebral soft-tissue mass but cannot reliably detect rupture and should not be used to exclude the diagnosis.
Ultrasonography is highly sensitive and specific for detecting AAA prior to rupture and is the imaging modality of choice in unstable patients, though sensitivity decreases once rupture has occurred.
CT scanning provides accurate measurement of aneurysm diameter, identifies rupture location, and guides operative planning. CT angiography is required when endovascular repair is being considered.
Differential Diagnosis
The differential diagnosis includes aortic dissection, renal or biliary colic, pancreatitis, cholecystitis, appendicitis, bowel obstruction, perforated viscus, mesenteric ischemia, diverticulitis, gastrointestinal hemorrhage, myocardial infarction, sepsis, adrenal crisis, spinal cord compression, and other abdominal arterial aneurysms.
Prehospital and Emergency Department Management
Prehospital care focuses on rapid recognition, establishment of two large-bore intravenous lines, and expedited transport to a facility with surgical capability. Early notification allows preparation of the operating room, blood products, and vascular surgery consultation.
In the emergency department, management includes cardiac monitoring, cautious crystalloid infusion, and early blood transfusion. Excessive fluid resuscitation should be avoided, as it may increase bleeding before surgical control. Once symptomatic AAA is suspected, emergent vascular surgery consultation and definitive operative repair—open or endovascular—are mandatory.
Disposition and Follow-Up
All patients with symptomatic AAA require immediate surgical intervention and hospital admission. Asymptomatic patients may be discharged only with reliable outpatient vascular surgery follow-up.
Discharge Instructions and Safety Netting
Patients should be instructed to seek immediate medical attention for new or worsening pain in the abdomen, back, flank, or lower extremities, as well as dizziness or syncope.
Clinical Pearls and Pitfalls
AAA must be considered in any patient presenting with abdominal, back, or flank pain, particularly older adults and smokers. Symptomatic aneurysms represent true surgical emergencies, and definitive care should never be delayed for additional diagnostic studies. Hemodynamically unstable patients should not be sent for CT imaging.
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