Aortic Aneurysm

The aorta is the largest artery in the body -- the main conduit through which oxygenated blood leaves the heart and reaches every organ. An aortic aneurysm is an abnormal, localised dilation of the aortic wall to more than 1.5 times its normal diameter. The word 'aneurysm' comes from the Greek for 'widening'.

What makes aortic aneurysms particularly dangerous is their silence. The great majority cause no symptoms until they are large enough to compress adjacent structures -- or until they rupture, at which point the mortality exceeds 80% even with emergency surgery. Most are found incidentally, during imaging performed for another reason, or through deliberate screening of high-risk groups.

Understanding the types, the size thresholds that determine when to act, how surveillance is structured, and what surgical options are available is essential for any patient who has been told they have an aortic aneurysm -- and for anyone in a high-risk group who has not yet been screened.

Understanding the Aorta

The aorta begins at the aortic valve of the heart and travels upward (the ascending aorta), arches over the heart (the aortic arch), then descends through the chest (the descending thoracic aorta) and into the abdomen (the abdominal aorta), where it divides at the level of the navel into the two iliac arteries supplying the legs.

Along its course, the aorta gives off branches to the coronary arteries (heart), the carotid and subclavian arteries (brain and arms), the celiac axis, superior mesenteric artery, renal arteries (abdominal organs and kidneys), and the iliac arteries (pelvis and legs). An aneurysm at any point in this course can jeopardise the organs supplied by the nearby branches.

The normal diameter of the abdominal aorta is approximately 2 cm. An abdominal aortic aneurysm (AAA) is defined as a diameter of 3 cm or more. The normal ascending thoracic aorta is approximately 3.5 cm; the normal descending thoracic aorta approximately 2.5 cm.

Aortic Aneurysm vs Aortic Dissection: An Important Distinction

Aortic aneurysm and aortic dissection are related but distinct conditions that are frequently confused. Both are life-threatening aortic emergencies, but their mechanisms and presentations differ.

An aortic aneurysm is a dilation of the entire aortic wall -- all three layers (intima, media, adventitia) expand outward together. The risk is rupture -- when the wall tears through completely, blood escapes into the surrounding cavity.

An aortic dissection is a tear in the inner lining (intima) of the aortic wall, creating a false lumen through which blood tracks between the intima and media. Dissection can occur in a dilated (aneurysmal) aorta or in a non-dilated aorta with a structurally weakened wall.

• Type A dissection: involves the ascending aorta -- a surgical emergency requiring immediate open surgery. Mortality increases by approximately 1-2% per hour without treatment.
• Type B dissection: involves only the descending aorta -- managed medically in uncomplicated cases (tight blood pressure control); endovascular stenting (TEVAR) for complicated cases with malperfusion or expansion.

The hallmark symptom of acute aortic dissection is sudden, severe, tearing or ripping pain -- often described as the worst pain the patient has ever experienced -- typically starting in the chest and radiating to the back. This requires immediate emergency assessment.

Symptoms and Presentation

The critical clinical fact about aortic aneurysms is that most have no symptoms until they are large, threatening structures, or have ruptured. This is why screening and surveillance are so important.

When an aneurysm is asymptomatic (most cases)

• No pain, no symptoms -- detected incidentally on ultrasound, CT, or MRI performed for other reasons
• A pulsatile mass felt in the abdomen on examination -- detectable in thin patients with AAA above approximately 5 cm
• Detected on routine health screening

Symptoms of a large or expanding aneurysm

• Deep, aching pain in the abdomen, lower back, or flank -- may be constant or intermittent
• Thoracic aneurysm: chest or upper back pain; hoarseness from compression of the recurrent laryngeal nerve; dysphagia from oesophageal compression; stridor from airway compression
• A sensation of pulsation in the abdomen
• Peripheral embolism -- clot from within the aneurysm sac travels distally, causing limb ischaemia or organ infarction

Symptoms of rupture or acute expansion -- emergency

• Sudden, severe abdominal, back, or flank pain -- classically described as tearing or ripping
• Rapid progression to haemodynamic shock: hypotension, collapse, loss of consciousness
• Distended or rigid abdomen
• Pain in the groin, leg, or scrotum from tracking haematoma

If any of these emergency symptoms occur in a patient with known aortic aneurysm -- or in a patient who is an older male with hypertension and smoking history -- call 995 immediately. This is a surgical emergency.

Causes and Risk Factors

Causes

• Atherosclerosis: The primary pathological process in AAA; lipid deposition and inflammatory changes in the arterial wall degrade the structural proteins elastin and collagen, reducing wall strength
• Hypertension: Chronically elevated blood pressure places greater mechanical stress on the aortic wall with each heartbeat, accelerating dilation
• Connective tissue disorders: Marfan syndrome (FBN1 gene mutation affecting fibrillin), Loeys-Dietz syndrome, Ehlers-Danlos syndrome vascular type; these cause intrinsic weakness of the aortic wall from early life
• Bicuspid aortic valve (BAV): Present in 1-2% of the population; associated with an abnormally elastic and dilated ascending aorta independent of any valve dysfunction
• Inflammatory aortitis: Giant cell arteritis, Takayasu arteritis, and other inflammatory vasculitides can cause aortic dilation
• Infectious (mycotic) aneurysm: Rare; caused by bacterial seeding of the aortic wall from endocarditis, syphilis, or direct infection
• Trauma: Deceleration injuries (road traffic accidents) can cause traumatic aortic transection, typically at the aortic isthmus

Risk Factors

• Smoking: The most powerful modifiable risk factor for AAA. Smokers have 3-5 times the risk of non-smokers. Active smoking accelerates aneurysm growth rate.
• Age: Incidence increases sharply above 65 years
• Male sex: AAA is 4-5 times more common in men; however, women have smaller baseline aortic diameters and rupture at smaller absolute sizes
• Family history: Having a first-degree relative with AAA approximately doubles the risk
• Hypertension: Directly drives wall stress and aneurysm growth
• Dyslipidaemia: Elevated LDL cholesterol accelerates atherosclerotic wall degeneration
• Pre-existing cardiovascular disease -- coronary artery disease and peripheral arterial disease frequently coexist with aortic aneurysm

Screening: Who Should be Tested

Because aortic aneurysms are asymptomatic until rupture, identifying at-risk individuals before the aneurysm reaches a dangerous size is the cornerstone of preventing rupture deaths. The following groups are recommended for screening:

• Men aged 65 and over who have ever smoked 
• Men aged 65 and over with a first-degree relative who has had an AAA
• Women aged 65 and over with a first-degree relative with AAA and who have risk factors (smoking, hypertension)
• Anyone with Marfan syndrome, Loeys-Dietz syndrome, or Ehlers-Danlos vascular type -- echocardiogram and CT or MRI of the entire aorta
• Patients with bicuspid aortic valve -- regular echocardiographic assessment of the ascending aorta
• Patients with known peripheral arterial disease or coronary artery disease -- aortic aneurysm frequently coexists
• First-degree relatives (siblings and children over 50) of patients with known AAA or thoracic aneurysm

Health screening packages at Farrer Park Hospital's HealthConnexion include abdominal ultrasound for assessment of the aorta and abdominal organs. Speak to your doctor about whether aortic screening is appropriate for you.

Reducing Your Risk

While genetic risk factors and age cannot be modified, several interventions significantly slow aneurysm growth and reduce the risk of cardiovascular events in patients with aortic aneurysm:

• Smoking cessation: The single most impactful intervention. Smokers with AAA who continue smoking have aneurysm growth rates 2-3 times higher than ex-smokers.
• Blood pressure control: Target below 130/80 mmHg. Beta-blockers directly reduce aortic wall stress by lowering heart rate and peak aortic pressure. ACE inhibitors and ARBs may have additional benefits.
• Statin therapy: Reduces LDL cholesterol, stabilises atherosclerotic plaques, and has anti-inflammatory effects that may slow aneurysm progression. Indicated for all patients with aortic aneurysm given their high overall cardiovascular risk.
• Antiplatelet therapy: Aspirin reduces the risk of cardiovascular events including myocardial infarction and stroke, which are the leading causes of death in patients with AAA.
• Diet and weight management: A Mediterranean diet reduces cardiovascular risk. Obesity increases aortic wall stress.
• Regular supervised exercise: Aerobic exercise at moderate intensity is safe for most patients with small to moderate aneurysms. Heavy straining (Valsalva manoeuvre during heavy lifting) is to be avoided as it transiently increases intra-aortic pressure.

How is an Aortic Aneurysm diagnosed?

• Abdominal ultrasound: The primary screening tool for AAA. Safe, non-invasive, inexpensive, no radiation. Highly accurate for measuring AAA diameter in the anteroposterior plane. Not suitable for thoracic aorta. Used for surveillance of known small AAAs.
• CT Angiography: The gold standard for pre-operative planning. Provides detailed 3D anatomy of the entire aorta and its branches -- essential for assessing aneurysm morphology, neck length, iliac access, and planning EVAR or TEVAR. Requires IV contrast and radiation dose.
• MRI/MR Angiography: Alternative to CT for aortic assessment without radiation. Particularly useful for younger patients or those with renal impairment or contrast allergy. Provides excellent soft tissue detail for connective tissue disease assessment.
• Transthoracic/Transesophageal Echocardiogram: Assesses the aortic root and ascending aorta at the time of cardiac examination. Transoesophageal echocardiogram gives superior imaging of the ascending and descending thoracic aorta. Used in Marfan syndrome surveillance and pre-operative cardiac assessment.
• Chest X-ray: A widened mediastinum or abnormal aortic contour on chest X-ray may suggest a thoracic aneurysm. Not a diagnostic test but may prompt further investigation. Calcification of the aneurysm wall may be visible.
• Conventional Angiography: Catheter-based aortography performed at the time of endovascular intervention. Provides real-time imaging of the aortic lumen and branches during EVAR/TEVAR deployment. Not used as a standalone diagnostic tool.