An arterial aneurysm is a localised abnormal dilatation of an artery due to a weakness in the arterial wall. The artery wall becomes weakened and balloons out. Arterial aneurysms can be classified as true or false aneurysms:

• True aneurysms:
  • True arterial aneurysms are often defined as a 50% increase in the normal diameter of the vessel.¹
  • Wall of the aneurysm consists of one or more of the vessel wall layers.
  • The artery wall can balloon out symmetrically to form a 'fusiform' aneurysm or there can be a local 'blow-out' to form a 'saccular' aneurysm.
  • Common sites are: abdominal aorta, iliac artery, popliteal artery, femoral artery.
• False aneurysms:
  • Represents a collection of blood, held around the vessel by a wall of connective tissue. The aneurysm does not involve the vessel wall.
  • May occur following trauma or there may be a slow leak of blood which is confined by surrounding tissues. False aneurysms may arise following angiogram, angioplasty or at the join between a graft and the artery.
  • False aneurysms result in a slowly expanding blood-filled cavity, which will eventually rupture or lead to thrombosis.
  • False aneurysms usually present as a pulsatile mass.

Aetiology

• Atherosclerosis
• Vasculitis (e.g. Kawasaki's disease)
• Syphilis
• Infective (may be due to either fungi or bacteria invading the vessel wall, and may be due to distant spread from infective endocarditis or from localised spread from adjacent structures)
• Penetrative or blunt trauma
• Congenital (e.g. berry aneurysm)
• Cocaine use has been associated with cerebral, aortic, visceral and peripheral aneurysms²

Epidemiology

• Aortic aneurysm found in 5-8% population aged >65 years.
• In England, abdominal aneurysm is responsible for over 11,000 hospital admissions and 10,000 deaths a year.¹

Risk factors

• Aortic aneurysm:
  • Atherosclerosis
• Cerebral aneurysms:
  • Anomalous vessels
  • Coarctation of the aorta
  • Polycystic kidney disease
  • Fibromuscular dysplasia
  • Connective tissue disorders
  • Vascular malformations and fistulae

Sites of aneurysms

• Cerebral aneurysms:
  • Most common are saccular aneurysm which are described as being berry-shaped swellings occurring at the bifurcation of arteries. Most aneurysms occur singly with the most frequent sites being the circle of Willis and the bifurcation of the middle cerebral artery. Cerebral aneurysms can be classified as:
    • Congenital saccular: arterial dilatations of less than 2.5 mm that appear in the bifurcation of the arteries of the circle of Willis.
    • Arteriosclerotic fusiform: caused by severe arteriosclerosis and arterial hypertension. The vessels of the circle of Willis are mainly affected. They are more frequent in the territory of the basilar and middle cerebral artery.
    • Mycotic: uncommon; caused by a septic degeneration of the elastic and muscular layer of the cerebral arteries.
    • Giant aneurysms: multifactorial origin with a diameter in greater than 2.5 mm. They are more common in the vertebral-basilar system.
  • Usually present with subarachnoid haemorrhage at age 40-60 years (children make up fewer than 2% of cases).
• Abdominal aortic aneurysms:
  • May be discovered incidentally as noticeable pulsation of aorta.
  • In 25% cases, there is co-existing arterial occlusive disease in renal or lower extremity arteries.
  • Ultrasound screening for abdominal aortic aneurysms fulfils all the criteria for a population screening programme, but only in men.³
  • Symptomatic aneurysms present as lower back pain and/or mid-abdominal pain together with prominent aortic pulsation suggest rapid growth of aneurysm with possible rupture.
  • Severe back, abdominal or flank pain with hypotension indicates a ruptured aneurysm. Up to 90% of patients die before reaching hospital or during or immediately after surgery.
• Thoracic aortic aneurysms (<10% of aortic aneurysms):
  • Most are asymptomatic but may present with substernal, back or neck pain.
  • May also develop dyspnoea, stridor or brassy cough, dysphagia, hoarseness or neck and arm oedema.
  • There may be a tracheal tug.
• Popliteal aneurysms:
  • Account for 80% of all peripheral aneurysms.
  • They are associated with aortic aneurysms and are often bilateral.
  • They cause symptoms from thrombosis, embolisation or compression of adjacent structures causing venous thrombosis or neuropathy.
• Femoral aneurysms:
  • Are the second commonest peripheral aneurysm.
  • Patients present with local pressure symptoms, thrombosis, or distal embolisation.
  • A pulsatile mass can be felt in the groin.
• Hepatic artery aneurysms:
  • Most common visceral artery aneurysm.
  • Often caused by medial degeneration of the hepatic artery, but also by trauma.
• Splenic artery aneurysms:
  • Fewer than 40% of all visceral aneurysms.
  • 4 times more common in women as in men.
• Renal artery aneurysms:
  • May be found in 1% of adults.
  • Are usually asymptomatic.

Dissections

A tear in the tunica intima results in blood splitting the tunica media. This produces a false lumen that can progress in an antegrade or retrograde direction. Rupture may occur back into the lumen or externally.

• Aortic dissection:
  • Result of an intimal tear causing a false lumen between the media and the adventitia. Over 90% occur in the ascending aorta either just distal to the aortic valve or the left subclavian artery.
  • Can rupture but more commonly dissection propagates distally, involving vessels branching off the aorta producing ischaemia in the kidneys, lower extremities, viscera or spinal cord (in descending order of probability).
  • Can also undergo antegrade extension to produce acute aortic regurgitation, myocardial infarction and cardiac tamponade.
  • Nearly all patients present with acute excruciating chest pain or pain in the top of the back. The pain may radiate down into the abdomen or groin or upwards into neck.
  • 80% of cases are associated with hypertension; other factors are Marfan's syndrome, pregnancy, bicuspid aortic valve and coarctation of the aorta.
• Carotid dissection:
  • Many occur extracranially in the internal carotid artery and, together with vertebral artery dissection, are a significant cause of stroke in younger patients.
  • Most cases have no known cause but may be associated in small proportion of patients with neck trauma or manipulation.
  • Carotid dissection may present with headache, neck and facial pain ipsilateral to dissection, which precedes development of a stroke. Episodes of transient blindness, syncope, swelling neck and pulsating tinnitus may also occur. Examination may reveal neurological deficits, Horner's syndrome (half of cases), hemiparesis, carotid bruit.

Investigations

• Aortic, peripheral and visceral aneurysms:
  • Abdominal ultrasound as screening study and follow-up for small <5 cm aneurysms.⁴
  • Aortography, MRI, CT scan. Computed tomography has a low specificity for determining the presence of a rupture and adds little information to routine clinical assessment.¹
• Left ventricular aneurysm: echocardiography, scintigraphy or angiography.
• Full assessment of cardiovascular status and cardiovascular risk factors.
• May need to consider vasculitis and connective tissue disorders so an ESR, CRP and autoantibody profile may be indicated.
• Assessment of renal function if possibly compromised by aortic aneurysm.
• Assessment of peripheral circulation using doppler.

Management

• Cerebral aneurysms:
  • Without operation, ruptured aneurysms carry high risk of another bleed with associated high mortality rate.
  • Aneurysms that have not ruptured should be considered for repair, usually by clipping artery, as may bleed at any time.
• Abdominal aortic aneurysms: see separate articles on aortic aneurysms and aortic dissection.
• Carotid dissection:
  • Treatment is dependent on the exact features of the condition.
  • Options include anticoagulant therapy and ligation of carotid artery.

Prevention

Primary and secondary prevention of cardiovascular disease.