Abdominal aortic aneurysms

AAA diameter (cm)	5-year risk of rupture (%/year)
<4.0 cm	0%
4.0–4.9 cm	0.5–5%
5.0–5.9 cm	3–15%
6.0–6.9 cm	10–20%
7.0–7.9 cm	20–40%
8.0 cm	30–50%

Table 36.2. Risk factors for AAA

Male sex (6:1)

Age older than 50 years

History of atherosclerotic disease

Family history of AAA in first-degree relative

Smoking (90% of AAA)

Hypertension

Hyperlipidemia

Previous aortic aneurysm

End-stage syphilis

Mycotic infections (immunosuppression, IV drug use, syphilis)

Presentation

Classic presentation

The classic triad of ruptured AAA is hypotension, pain, and pulsatile abdominal mass. This occurs in only half of the patients.
Typical pain is usually described as abdominal or lower back.
Any patient with these symptoms and a known AAA is at risk for imminent rupture, if rupture has not already occurred.
Vital sign stability should not be reassuring as these patients can deteriorate rapidly.
Hypotension is the least consistent part of the triad, occurring in as few as one-third of patients.
Atypical presentations are common. Inflammatory aneurysms may present with fever or weight loss. Patients may complain of pain in the chest, thigh, inguinal area, or scrotum.
Initial blood loss may be minor and the patient may present with normal vital signs. Vital sign stability should not necessarily be reassuring as these patients can deteriorate rapidly.

Critical presentation

Rupture is often the first symptom of patients with AAA and is usually experienced as severe abdominal or back pain, especially lumbar pain.
Pain is often described as severe or abrupt in onset, and characterized as a ripping or tearing sensation radiating to the back.
Bleeding can lead to hemorrhagic shock with hypotension, altered mental status, syncope, and sudden death.
Signs of rupture:
- Hypotension
- Periumbilical ecchymosis (Cullen’s sign)
- Flank ecchymosis (Grey–Turner’s sign)
- Scrotal or vulvar hematomas.
Less common but critical presentations of AAA include
- Extremity ischemia due to peripheral embolization of a thrombus from within the aneurysm
- Complete aortic occlusion
- Aortic fistulization:
  - Aortoenteric fistulas within the duodenum can present with unexplained upper or lower GI bleeding.
  - Aortovenous fistulas into the inferior vena cava can present as high-output heart failure with lower-extremity edema, dilated superficial veins, decreased peripheral blood flow, and renal insufficiency with hematuria.
- Disseminated intravascular coagulation (DIC).

Diagnosis and evaluation

Physical examination
- As above, vital signs may be normal early in the course of disease but hemodynamic decompensation can occur very rapidly.
- Physical examination may be unremarkable, and the classic finding of a palpable abdominal mass is not always appreciated.
- In the lower extremities, a widened pulse pressure may suggest the presence of AAA.
- A benign clinical examination is not considered reliable enough to rule out AAA. Factors such as size of the AAA and the patient’s body habitus may disguise underlying pathology.
Diagnostic tests
- Laboratory tests:
  - No specific laboratory studies exist that can be used to make the diagnosis of abdominal aortic aneurysm.
  - Patients presenting with a ruptured AAA may have anemia, but a normal hemoglobin certainly does not rule out even ruptured AAA.
  - In mycotic aneurysms, blood cultures are often positive and reveal the nature of the infecting agent.
- Abdominal radiography:
  - Although symptomatic aneurysms are usually large and often calcified, abdominal radiography is not the preferred method as it has low sensitivity and specificity for detecting AAA when compared with ultrasound and CT.
  - If an abdominal aortic aneurysm is appreciated on the radiograph, the most common findings are paravertebral soft tissue mass or calcification of the aortic wall.
- Ultrasound:
  - Ultrasound (US) is the preferred method of screening with 100% sensitivity in detecting AAA.
  - Compared with computed tomography, US is low in cost and has no radiation or contrast exposure.
  - In the emergent setting, US can be performed at bedside to evaluate a patient with potential ruptured AAA, averting the need to take an unstable patient to the radiology suite.
  - Bedside US must contain views of the aorta along the entire course for appropriate diagnosis. Patients with a normal diameter throughout the course of the abdominal aorta likely do not have AAA.
  - This technique is limited by obesity, bowel gas, and abdominal tenderness.
  - Operator dependency is a major disadvantage of the US study.
    - Depending on the level of skill and experience the US examination is more prone to interpretive or technical error.
    - Patient habitus may also cause inaccurate results secondary to inconsistent views of the aorta.
  - Although US is sensitive in detecting AAA, it cannot be relied on to determine whether there has been a rupture of the AA. Free intraperitoneal or retroperitoneal blood in the presence of other clinical symptoms may be suggestive of rupture but it is not always appreciated.
- Computed tomography (CT):
  - 100% accurate in determining the presence and exact size of AAA.
  - CT is more sensitive than other imaging modalities in detecting retroperitoneal hemorrhage associated with aneurysm.
  - IV contrast is not necessary to identify aneurysm and acute hemorrhage is well visualized on scans done without contrast.
  - During AAA rupture, blood is often seen as retroperitoneal fluid located adjacent to the aneurysm, often tracking into the perinephric space or along the psoas muscle.
  - The crescent sign (layering blood within aorta) indicates an impending rupture.
- Contrast aortography:
  - This was the gold standard prior to widespread use of modern CT scanners.
  - Used for evaluation of aneurysms before elective surgery.
  - Carries risk of complications, such as bleeding, allergic reactions, atheroembolism, and nephrotoxicity.
  - Useful in documenting length of the aneurysm, especially upper and lower limits, and the extent of associated atherosclerotic vascular disease.
  - The presence of mural clots may reduce the luminal size; thus, aortography may underestimate the diameter of an aneurysm.
- Magnetic resonance imaging (MRI):
  - MRI is minimally invasive and, when combined with magnetic resonance angiography (MRA), can provide excellent details for the preoperative evaluation of AAAs.
  - MRI has 100% sensitivity in detecting aneurysms, and successfully identifies the proximal and distal extent of the aneurysms, the number and origins of renal arteries, and the presence of inflammation.
  - The use of MRI is not realistic for unstable patients due to the length of time required to obtain the images and the difficulty accessing and monitoring the patient.

Critical management

Ruptured AAA is fatal unless treated surgically. Hemodynamically unstable patients should be taken to the OR as soon as possible and diagnostic testing should be kept to a minimum.
Unstable patients should have standard resuscitative measures (e.g., large-bore intravenous access, cardiac monitoring, supplemental oxygen, blood type and cross-matching, vasopressors) while preparing for transfer to the operating room.
Symptomatic patients with known AAA should be evaluated by vascular surgery regardless of the AAA size.
Surgical management
- Patients may be taken to the OR on the basis of clinical suspicion as testing may delay treatment and increase the risk of death.
- Patients taken to the OR as soon as possible after arrival in ED have a higher chance of survival than those patients who have had delayed OR times because of stabilization in the ED.
- There is a 50% operative mortality rate in patients with ruptured AAA.
- The vascular surgeon may choose to repair via open approach with laparotomy or endovascular technique.
  - Open AAA repair requires direct access to the aorta through an abdominal or retroperitoneal approach.
  - Endovascular repair of an AAA involves gaining access to the lumen of the abdominal aorta, usually via small incisions over the femoral vessels.
  - An endograft, typically a cloth graft with a stent exoskeleton, is placed within the lumen of the AAA, extending distally into the iliac arteries.
Nonemergent treatment and monitoring
- Nonemergent management is summarized in Table 36.3. The patient must be compliant with follow-up in order to be safely managed expectantly.
- AAAs greater than 5 cm are at greatest risk for rupture and should be referred to a vascular surgeon for prompt evaluation (outpatient evaluation only if asymptomatic).
- In patients with a small AAA, reduction of the expansion rate and rupture risk can be accomplished with smoking cessation, blood pressure control, and beta blockade.
Complications of repair
- With more patients living longer after AAA repairs, more and more of these patients will present to the ED with complications from the repair.
- Graft infection:
  - Infection can disrupt the anastomosis between native artery and the graft leading to leakage of blood and pseudoaneurysm formation.
  - Subtle signs of graft infections include low-grade fever, abdominal, or back pain.
  - Patients may also present in florid septic shock due to bacteremia.
  - CT should be performed to evaluate possible infection. Findings consistent with graft infection include fluid or gas collections adjacent to the graft.
- Aortoenteric fistula (AEF):
  - AEF most commonly presents as gastrointestinal bleeding.
  - Severity of bleeding can range from occult to massive.
  - An AEF must be considered in any patient with GI bleeding and history of abdominal aortic surgery.
  - In an unstable patient, diagnostic testing may be averted in lieu of laparotomy or angiography.
  - In a stable patient upper endoscopy and/or CT may be useful diagnostic adjuncts.
  - Patients with AEF may also get secondary graft infection.
- Pseudoaneurysm:
  - Occurs at the site of leaking anastomosis.
  - Most commonly it is due to degeneration of the native vessel but can also be seen with both graft infection and AEF.
  - Patients may present with pain or pulsatile mass in the abdomen or groin.
  - Complications of pseudoaneurysm formation include rupture and downstream embolic phenomena.
  - Patients with suspected pseudoaneurysm may be evaluated with CT, US, and/or angiography.
- Aortocaval fistula:
  - Aortocaval fistula is a surgical emergency.
  - Spontaneous aortocaval fistula is rare and occurs in only 4% of all ruptured AAA.
  - Physical signs may be subtle or vague. The presence of low back pain, machinery-like abdominal murmur, and high-output cardiac failure unresponsive to medical treatment should raise the suspicion.
  - Preoperative diagnosis is crucial, as adequate preparation is needed because of the massive bleeding during surgery.
  - Successful treatment depends on management of perioperative hemodynamics as well as control of bleeding from the fistula.