Aortic Aneurysm – Causes, Symptoms, Treatment

An aortic aneurysm is the abnormal dilation of a segment of the aorta. Abdominal aortic aneurysm is the most common aortic aneurysm, occurring frequently in the infrarenal area. Degenerative aortic disorders are the prevalent etiology, affecting patients > 60 years of age. Most aneurysms are asymptomatic, but can cause compression of surrounding structures or rupture, which is a life-threatening emergency. Diagnosis is often made by ultrasound. As aneurysmal rupture carries a high mortality rate, surveillance is recommended for asymptomatic cases to monitor aortic diameter. Elective surgery (the majority via endovascular aortic repair) is an effective way to reduce complications and aneurysm-related death. This surgery is performed based on aortic size, underlying condition, and associated symptoms.

• Abdominal aortic aneurysm (AAA): infradiaphragmatic dilation of the aorta (to an aortic diameter of ≥ 3 cm)
• Types:
  • True aneurysm: dilation of the aorta involving all 3 layers (intima, media, adventitia)
    • Fusiform-shaped: bulges on all sides of the aorta (more common)
    • Saccular-shaped: bulges on 1 side
  • Pseudoaneurysm:
    • Dilation caused by a disruption of the aortic wall
    • Extravasated blood contained by periarterial connective tissue, not by all wall layers
    • Extravascular hematoma communicates with the intravascular space.
• Location:
  • Suprarenal: involves visceral arteries; below the chest
  • Pararenal: involves origin of the renal arteries
  • Juxtarenal:
    • No aneurysm in origin of renal arteries but aneurysm starts just beyond renal arteries
    • No normal aortic segment between renal arteries and aneurysm
  • Infrarenal (most common):
    • Below renal arteries
    • There is a normal aortic segment between renal arteries and aneurysm.

Epidemiology

• AAAs: more common than thoracic aortic aneurysms (TAAs)
• In the United States:
  • More than 50% of patients with ruptured AAA die before reaching the hospital.
  • Over the past 30 years, AAA-related mortality has decreased, possibly due to:
    • Disease screening
    • Decline in smoking
    • Use of endovascular aortic repair

Etiology

• Degenerative disorders:
  • Most common cause of AAA
  • Risk factors:
    • Age (> 60) and male sex
    • Smoking
    • Atherosclerosis (more common in AAA)
    • Hypertension
    • Caucasian race
  • Decreased risk noted in: females, non-Caucasians, and patients with diabetes
• Genetic or developmental disorders:
  • Marfan’s syndrome
  • Turner’s syndrome
  • Ehlers-Danlos syndrome
  • Loeys-Dietz syndrome
  • Polycystic kidney disease
• Family history of AAA and presence of other arterial aneurysms (popliteal, femoral, intracranial)
• Vasculitis:
  • Giant cell arteritis
  • Behcet’s disease
  • Takayasu’s arteritis
  • HLA-B27–associated spondyloarthropathies
• Infection:
  • Syphilis (tertiary)
  • Tuberculosis
  • Mycotic (Salmonella, staphylococcal, streptococcal, fungal infection)
• Trauma: includes prior aortic procedure

Pathophysiology

Contributing factors

• Embryology:
  • Embryologic origin can affect the response of aorta to cytokines and growth factors.
  • Abdominal aorta: derived from mesoderm
• Genetics:
  • 20% from familial predisposition
• Biomechanics, structure, and growth of artery:
  • Wall thickness of aorta decreases from the thoracic area to the distal aorta
  • Abdominal aorta:
    • Lower elastin, collagen content
    • Has avascular media (poor nutrition delivery)
    • Grows by ↑ thickness of lamellar units
    • Fewer lamellar units = more tension per lamellar unit
    • ↑ pulse pressures and more wall shear stress:
      • Noted in distal aorta, especially infrarenal aorta (most common location of aortic aneurysm)
• Atherosclerosis:
  • AAA is associated with severe atherosclerosis.
  • High likelihood of progression of fatty streak to atheroma (compared with TAA)
• Inflammation affects both TAA and AAA:
  • Predominantly T cells and macrophages
  • In AAA, both pro- and anti-inflammatory cytokines noted
• Proteolysis by matrix metalloproteinases (MMPs):
  • ↑ breakdown of extracellular matrix
  • MMP-9 proportional to aneurysm diameter
  • MMP-2: ↑ growth of aneurysm

Pathogenesis

• Regular vascular remodeling (synthesis, degradation, and repair) of extracellular matrix (ECM) components maintain the functional and structural integrity of the artery.
• Above factors, in combination with age and environment (i.e. smoking, trauma) → result in breakdown of ECM → arterial medial degeneration → weakened vascular wall → dilation
• The dilation + rapid expansion of aorta: ↑ risk of rupture or aortic dissection
• Widening of the vessel disrupts laminar blood flow → turbulence + inflammation → possible thrombus formation within the vessel (with risk of embolism)

Clinical Presentation

Symptoms

• Commonly asymptomatic
• Depending on size and location:
  • Compression or erosion of surrounding structures: pain in the abdomen, lower back/flank (most common manifestations)
  • Rupture typically into retroperitoneum: sudden severe flank or back pain
  • Distal abdominal aneurysm compression and/or rupture: pelvic, groin or thigh, lower extremity pain
  • Thromboembolic events: claudication (limb ischemia), painful pulseless extremity (embolism)
  • Aortoduodenal fistula: upper gastrointestinal bleeding
  • Aortic infection: fever, weight loss, vague abdominal pain
  • Inflammatory aneurysm: patients are younger; abdominal and/or back pain

Signs

• AAA often found incidentally in imaging studies
• AAA rupture:
  • Life-threatening emergency!
  • Hypotension, tachycardia
• Pulsatile abdominal mass (in 62% of ruptured AAAs)
• Abdominal tenderness, abdominal bruit on examination
• Ecchymosis (sign of retroperitoneal hematoma and blood extravasation into subcutaneous tissues)
  • Flank (Grey-Turner sign)
  • Proximal thigh (Fox’s sign)
  • Periumbilical (Cullen’s sign)
  • Scrotum (Bryant’s sign)
• Reduced femoral and pedal pulses in thromboembolism

Diagnosis

History

• Risk factors (hypertension, smoking, hypercholesterolemia)
• Family history of aortic pathology
• Known history of aneurysm in other areas (intracranial, iliac, femoral, popliteal aneurysms)
• Prior aortic dissection
• Other conditions: Marfan’s syndrome, Loeys-Dietz syndrome, Ehlers-Danlos syndrome, and other connective tissue diseases
• Prior aortic procedure

Diagnostic tests

• Abdominal ultrasound:
  • Used for screening, diagnosis, and serial measurements
  • Determines the location and size of aneurysm
  • Screening:
    • Best initial step for asymptomatic patients
    • 1-time ultrasound is:
      • Recommended in men aged 65–75 years who have smoked
      • Suggested in women and men aged 65–75 years with family history of AAA or AAA rupture
  • Symptomatic patients: can be used bedside in unstable patients
  • Diagnosis of aneurysm: > 3 cm outer aortic diameter
  • Limited in detecting rupture, leakage, and other vessel involvement
  • Affected by body habitus and bowel gas
• Abdominal computed tomography (CT) with contrast:
  • For stable symptomatic patients and planning operative repair
  • Defines extent of aneurysm, leakage, rupture, vessel involvement
  • Signs of impending rupture:
    • Hyperattenuating crescent sign (93% specificity)
    • Thrombus fissuration
    • Aortic blebs from surface of aorta
    • Irregular aortic wall
    • Draped aorta sign (rupture sealed by vertebral body)
  • Signs of rupture:
    • Intra- and/or retroperitoneal hematoma
    • Periaortic stranding
    • Indistinct aortic wall
• Magnetic resonance imaging (MRI):
  • No radiation or dye (may be used for patients with contrast allergy)
  • Limited availability and higher cost
• Arteriography:
  • Cannot accurately measure aortic diameter
  • Used intraoperatively (endovascular repair)

Management

Non-surgical management

• Reduce cardiovascular risk:
  • Smoking cessation (most effective nonsurgical intervention to reduce aneurysm-related complications and death)
  • Exercise:
    • Avoid heavy lifting.
    • Avoid activities that lead to Valsalva (↑ blood pressure).
  • Hypertension control:
    • Antihypertensives given to reach recommended blood pressure goals
    • Unlike TAA, no specific medication recommended to limit AAA expansion
  • Lipid control with statins (target LDL < 70 mg/dL)
• Avoid fluoroquinolones (may ↑ risk of dissection or rupture)
• Surveillance: Asymptomatic AAA < 5.5 cm, periodic evaluation and aneurysm diameter surveillance

Surgical management

Indications for operative repair

• AAA rupture: emergency repair
• Elective repair: most effective way of preventing rupture and aneurysm-related death
  • Symptomatic AAA
  • Rapidly expanding (> 0.5 cm/6 months or > 1 cm/1 year)
  • Asymptomatic AAA:  when diameter ≥ 5.5 cm  (5 cm in women: higher rate of rupture)
  • AAA with coexisting iliac, femoral, or popliteal artery aneurysm
  • AAA associated with symptomatic peripheral arterial disease (PAD) undergoing revascularization

Operative options

• Open surgical repair: 
  • Midline transperitoneal or retroperitoneal incision
  • Diseased aorta replaced with tube or prosthetic graft
  • Indicated for younger patients, low perioperative risk, or those who have contraindications for endovascular aortic repair (EVAR)
  • Higher perioperative mortality but long-term durability
  • Surveillance: CT angiography 5 years later, look for aortic dilation or pseudoaneurysm
• EVAR:
  • In the United States: 80% of AAA surgical repair
  • Access through iliac or femoral arteries and endograft placed within AAA lumen
  • Requires anatomic suitability (site and structure of aneurysm and access vessels)
  • Decreased operative mortality but higher rate of re-intervention
  • Surveillance:
    • CT angiography 1 month and 1 year post-operatively, then duplex ultrasonography/CT annually if with uncomplicated surgery
    • Look for endoleak, sac enlargement, migration of stents, and device integrity

Differential Diagnosis

• Ruptured viscus: a condition in which gastrointestinal wall integrity is lost with subsequent leakage of enteric contents into the peritoneal cavity, resulting in peritonitis. A ruptured viscus is life-threatening and requires surgical management.
• Mesenteric ischemia: a rare, life-threatening syndrome caused by inadequate blood flow through the mesenteric vessels resulting in ischemia and gangrene of the bowel wall. Mesenteric ischemia can be acute or chronic. Acute mesenteric ischemia is a surgical emergency, while the chronic condition requires risk factor modification, as it is related to vascular disease.
• Strangulated hernia: Hernias are protrusions of abdominal content (peritoneum, visceral fat, and/or viscera) through a congenital or acquired defect in the abdominal wall. Strangulation involves the constriction of hernial contents leading to bowel ischemia and requires emergency surgery to avoid bowel loss, perforation, and sepsis.
• Acute cholecystitis: a condition characterized by inflammation of the gallbladder, most often due to obstruction of the cystic duct by a gallstone. Management includes IV fluids, pain control, and IV antibiotics for secondary infection. Complicated cholecystitis and progressive symptoms are indications for emergency cholecystectomy.
• Acute pancreatitis: an inflammation of the pancreas that typically causes epigastric pain that radiates to the back. This condition is often treated with aggressive fluid resuscitation, bowel rest, and pain control. Surgery is indicated if the condition is associated with gallstones.
• Diverticular abscess: a group of various intestinal conditions characterized by abnormal outpouchings of the colonic mucosa (diverticula). Over time, these diverticula may accumulate intestinal content, become infected, swell, and develop into an abscess. Intravenous antibiotics are the recommended treatment, with percutaneous drainage needed for large abscess or failed medical treatment.