An aneurysm is a loss of vascular wall strength which results in separation of the layers that lead to swelling and possibly rupture. High pressure, large arteries cause the greatest risk for sudden exsanguination and death. Of these, the aorta is the largest.
An aneurysm diagnosis is established when the full-thickness dilation of a blood vessel is >50% larger than its normal diameter (2-3 cm). For clinical purposes, aortic aneurysm is recognized to have a diameter > 3 cm. Its risk factors are:
- Male gender
- Family history
- Presence of aneurysms elsewhere
Use of Ultrasound in Aortic Aneurysm
Screening via ultrasound to measure aortic diameter is used in men aged 65-75 who had ever smoked, or (regardless of smoking history) who who have/had a close relative who had required surgical aortic aneurysm repair or who had died from rupture.
Once diagnosed, the stability or progress of an aortic aneurysm can be followed by ultrasound over time, and if there is progression, can indicate the time that surgical intervention is prudent to avert a catastrophic rupture.
Symptoms of Aortic Aneurysm
In the abdomen, aortic aneurysm does not usually cause symptoms unless it is actively expanding, compresses surrounding structures, is inflamed, or ruptures. When present, symptoms include abdominal, back, or flank pain, distention, and hemodynamic changes.
In the thoracic cavity, aortic aneurysm, following the same symptom-causing provocations as with abdominal aneurysms, can result in sudden chest, back, or abdominal pain. Dyspnea can occur if there is compression of the pulmonary trachea or bronchi.
Repair of either abdominal or thoracic aortic aneurysms is indicated with symptomatology or if a critical diameter is breached which raises the risk of rupture to unacceptable levels.
Diagnosis of Aortic Aneurysm
Most patients are not aware of an aneurysm at diagnosis. The diagnosis is gleaned from an incidental ultrasound for unrelated reasons or a pulsating mass is noted on an otherwise routine physical exam.
Aortic aneurysm can progress to rupture without warning or predictive symptoms. For this reason, screening is important for groups at risk:
- Asymptomatic patients with risk factors for aneurysm: smoking, male gender, advanced age, Caucasian, atherosclerosis, family history of aneurysm, or connective tissue disorder (Marfan, Ehlers-Danlos, Loey-Dietz syndromes) in the patient or family.
- Physical exam that demonstrates a pulsating abdominal mass or aneurysms in places other than the aorta.
- Signs and symptoms: such as abdominal, chest, or back pain, limb ischemia, different blood pressures in opposite limbs, etc.
Emergency vs. Non-Emergency Diagnosis
Whether ultrasound of the aorta or more involved testing such as CT are used depends on the presentation.
- Ultrasound: In emergencies, bedside ultrasound offers the fastest assessment in hemodynamically unstable patients that can prompt the decision for sending them to the OR. Ultrasound is also useful in screening and in following patients with an established diagnosis.
- CT Scan: Alternately, symptomatic aneurysm patients who are stable are usually evaluated with the addition of CT scans.
Currently, “biomarkers” for inflammatory changes associated with aortic aneurysms are not useful. These include white blood cell count, fibrinogen level, D-dimer, troponin T, N-terminal pro-brain natriuretic peptide, and C-reactive protein (CRP). On-going research is being conducted in attempts to relate abnormal levels of these to the presence of aneurysms, which may make them important diagnostic and predictive measures in the future. Genetic testing is helpful in identifying congenital connective tissue disorders that are prone to aortic wall weakening, such as Marfan and other syndromes.
Management of an Aortic Aneurysm
Management and treatment of an aortic aneurysm is guided by two parameters:
- Symptomatic vs. asymptomatic
- Hemodynamically stable vs. unstable
The most conservative measures are used for those who are asymptomatic and hemodynamically stable. An asymptomatic but diagnosed aneurysm is followed by CT measurements, but if signs or symptoms become emergent, ultrasound–even bedside ultrasound–are the most rapid way to determine if timely surgical preparation is necessary.
An aneurysm diagnosis is established when the full-thickness dilation of a blood vessel is >50% larger than its normal diameter (2-3 cm). For clinical purposes, aortic aneurysm is recognized to have a diameter > 3 cm. Regardless, if the aneurysm has a diameter measurement of >5.5 cm, or if serial measurements determine that it is expanding at >1/2 cm/year, surgical treatment is indicated due to the high risk for catastrophic, life-threatening rupture.
Only 1/2 of patients with a ruptured aneurysm survive, making pre-emptive management and treatment necessary once the diameter measurements indicate the patient’s transition into a higher risk category.
Pain management is indicated for those with symptomatic aneurysm who are stable. The physician must be careful to not mask the pain completely as a change in pain perception could indicate rapid expansion or imminent rupture.
Invasive Repair of Aneurysm
There are two methods of repairing an aneurysm, based on inclusive or exclusive criteria, once there is an urgent or emergency scenario in play:
- Open repair: Replacement of the aortic segment with a graft through an incision.
- Endovascular aneurysm repair (EVAR): Placement of a modular graft through threading it via the iliac or femoral arteries, to wall off the aneurysm sac from the circulation.
Aortic Aneurysm Prevention
In connection with aortic aneurysm and ultrasound, prevention is centered on predicting when a patient crosses over the risk stratification for rupture.
Once the aorta aneurysm diameter approaches 6 cm, the aorta loses elasticity to the point that any increases in blood pressure, e.g., exercise, could easily exceed the maximum containment of the weakened wall, causing rupture. In the abdominal aorta, the critical diameter for surgical prevention of rupture is when it exceeds 5.5 cm or when the diameter has reached an expansion rate of greater than a half-centimeter a year. This is determined via ultrasound or CT scan. Such a measurement (or less, when the aneurysm is symptomatic), calls for repair. At this diameter, the risk of the surgery becomes less than the risk of having a pre-ruptured aneurysm. In the thoracic aorta, like that of abdominal aortic aneurysms, the risk of rupture exceeds the risks in surgical repair once the diameter exceeds 5.5 cm or when the expansion rate exceeds 1 cm/year. CT or MRI are used if time and urgency allow.
Dissection is a feature associated with aortic aneurysm in which the layers of the aortic wall separate due to the extravasation of blood from a tear in the inner aortic layer (the “intima”). This will affect, diminish, or even obliterate arterial blood flow in the branching arterial supply involved at the dissecting segment. Distal organs to this development are at risk for ischemia and necrosis. Prevention of ischemia due to this compromise in perfusion is addressed via surgery.