Definitions
An aneurysm is an artery that has a localised dilation, with a permanent diameter of >1.5x that expected of the particular artery.
True Aneurysm – the wall of the artery forms the wall of the aneurysm
- The most frequently involved arteries are; in decreasing incidence: abdominal aorta, iliac, popliteal, femoral and thoracic aorta
False aneurysm – aka – pseudoaneurysm - other surrounding tissues form the wall of the aneurysm
- These most commonly occur in the femoral artery following femoral artery puncture. If there is inadequate pressure to the entry site of the puncture, then blood can spill out and form a haematoma. Eventually the surrounding soft tissue will form the wall of the aneurysm.
- I think – the difference between this and a true haematoma is that in a pseudoaneurysm there is still communication between the lumen and the fluid collection, but in a haematoma, there is either no connection, or just a one way 'leakage' of fluid..
Aneurysms can either be fusiform or sac-like.
- Fusiform describes a shape that is tapered at both ends (a bit like a raindrop with a pointy bit at both ends), whilst sac-like describes a more rounded characteristic.
When inspecting an aneurysm you should feel for them being expansile. This means they expand and contract. Swellings that are pulsatile are different – these do not expand and contract but just transmit the pulse – e.g. nodes overlying arteries.
Aetiology
Despite the different pathology between aneurysmal and atheromatous disease, the risk factors for both are similar, and include:
- Hypertension
- Smoking
- Age
- Diabetes
- Obesity
- High LDL levels
- Sedentary lifestyle
- Genetic factors – are more important in aneurysmal disease than in atherosclerotic disease, although they have a role in both.
- 10% of cases have a first-order relative also with the condition
Specific aetiological factors for aneurysm include:
- Co-arctation of the aorta
- Marfan’s syndrome, and other connective tissue disorders
- Previous aortic surgery
- Pregnancy (particularly 3rd trimester)
- Trauma
- Incidence increases with age – 5% of men over 60 have one
- Occur 3-5x more often in men than women
Complications
Aneurysms in themselves do not often constitute a primary problem. They may cause a local obstruction (e.g. of IVC), and they can also cause impaired bloodflow to the lower limbs. They are also a risk factor for thrombosis and embolism. However, the main risk comes from the tendency of aneurysms to dissect and rupture – most commonly an aortic aneurysm will rupture into the retroperitoneal space.
- Elective repair of aneurysms before rupture is comparatively safe
- Repair after rupture has very high mortality
40% of AAA patients also have iliac artery aneurysms, and 15% have popliteal aneurysms.
General Features of aortic aneurysm
Often symptomless, and discovered incidentally (examination, AXR, ultrasound, CT)
- Mean age of presentation – 65
- Often discovered on AXR – about 65% of cases are sufficiently calcified to show up on radiograph
- Ultrasound is usually used to ‘stage’ the aneurysm. It is accurate at assessing the site of the aneurysm, and easy to follow up cases to asses development. CT is more accurate, and particularly useful at looking at the surround structures (e.g. to see if there is any compression) but more expensive, thus is usually used only for pre-op assessment.
Risk of dissection (bursting). Risk increases with the diameter of the aneurysm
A source of thrombus formation, which can embolise to the lower limbs
- Rarely, may be completely occluded by thrombus
Management of aortic aneurysm
The nice guidelines state that an aortic aneurysm of greater than 5.5cm in diameter should be treated. Below this size, the risk of dissection is outweighed by the risk of surgery.
- At 5.5cm the annual risk of rupture is 25%
- At 6.5cm it is 35%
- At >7cm it is 75%
In some cases, symptomatic aneurysms of smaller size may be operated on.
- Pain is thought to be a risk factor for rupture
- Thrombo-embolus is also an indication for surgery – and can prevent limb-loss.
Sugery is the treatment of choice. There are two options:
Open Laparotomy - the affected segment of aorta may be clamped and replaced by a prosthetic segment, (most common a Dacron graft). Graft failure is rare. In a variation of the treatment, the affected artery segment is bypassed.
- Complications are generally rare. There may be kidney problems, and sometimes paraplegia or ischaemic colitis. fistula formation with the small bowel can also occur but is rare. Infection is also rare.
Mortality
- 5-8% in elective asymptomatic AAA
- 10-20% for symptomatic emergency AAA
- 50% for ruptured AAA
- Long-term survival for most patients is almost identical to the general population
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