Aneurysm and AAA
- General Features of aortic aneurysm
- Management of aortic aneurysm
- Dissection and Rupture of AA
- Marfan’s syndrome
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..
- 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.
- 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
- Co-arctation of the aorta
- Marfan’s syndrome, and other connective tissue disorders
- Previous aortic surgery
- Pregnancy (particularly 3rd trimester)
- Incidence increases with age – 5% of men over 60 have one
- Occur 3-5x more often in men than women
- Elective repair of aneurysms before rupture is comparatively safe
- Repair after rupture has very high mortality
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.
- 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
Endoluminal surgery – EVAR - Endovascular aneurysm repair - an aortic graft is inserted through the femoral artery, and up into the abdominal aorta. This method is generally preferred (lower mortality 1.2%) but many patients are not suitable. There must be at least 2.5cm normal aorta between the aneurysm and the renal arteries to securely fix the graft in place.
- complications with the actual graft are more common with the endoluminal technique than with open surgery. the graft can fail, or it may be moved, allowing blood to refill the aneurysm. Although, the risks of the procedure itself are far less than open surgery.
- Generally, rupture cannot be treated by the endoluminal method, although there are ongoing trials.
Dissection and Rupture of AA
Death rates from this rises with age:
- Age 55-59 – death rate is 12.5 per 100 000
- Age 80+ - death rate is 273 per 100 000
>75% with a ruptured AAA die – usually before getting to hospital.
Of those that do reach hospital, surgery has a 50% mortality rate. Thus only around 10% of those with a ruptured AAA will survive.
- Dissection is where blood escapes through the innermost layer of the wall of the artery, and prises apart the media, creating a new lumen. Sometimes, this lumen is absorbed back into the main lumen, creating a ‘double-barrelled aorta’. This may be stable, but may rupture. If it is close to the aortic valve (thoracic aortic aneurysm) it may compromise valve function.
- The dissection is sometimes able to track back all the way to the pericardium, and can cause haemopericardium.
Classification of dissecting AA
- Type A – 2/3 of cases. These involve the ascending aorta, and may also include the descending aorta
- Type B –affect the descending aorta only
- Sudden onset, severe pain. Often described as tearing¸ and usually radiates to the back.
- Pain usually follows the line of the dissection
- Ascending aorta – pain will be in the chest
- Descending aorta – pain often in the back
Collapse (due to hypotension)
Expansile (not pulsatile) mass in the abdomen
Other signs may include:
- Testicular pain
- Symptoms similar to renal colic
- Symptoms similar to diverticulitis
- Non-specific back pain – this results from gradual erosion of the vertebral bodies in patients with long-standing aneurysm.
- If in doubt about the diagnosis; assume ruptured AA!
- Mortality in dissection is about 1% per hour
- This is much higher if it progresses to rupture!
- Type A – require Emergency surgery – usually by open surgery (Dacron Graft). for further details see above : ‘Management of aortic aneurysm’
- Type B – often not quite as urgent as type A – depending on the individual case. Possibility to treat endoluminally, although open surgery is often still the treatment of choice.
Abdominal Aortic Aneurysm
Usually in the infrarenal segment of the aorta (80%)
These most commonly occur below the level of the renal artery
Features of pain:
- Rapid expansion or rupture will cause epigastric pain radiating to the back. Pain may also be present in the groin, iliac fossae and testicles.
- Can be a constant or intermittent pain
- Be careful not to dismiss it as renal colic!
Thoracic Aortic Aneurysm
- Asymmetrical brachial/radial/carotid pulses if the dissection involves the aortic arch. Variable pattern depending on where the dissection is.
- BP may be different in each arm – under similar circumstances to the above.
Pathology of aneurysm
Most probably pathology
- There is ischaemia of the aortic media where there is an atherosclerotic plaque. This is as a result of release of macrophage enzymes (released when macrophages become activatived) that break down the elastic fibres (collagen and elastin)
- There is evidence that various genetic variants of collagen are more susceptible, and this probably accounts for the familial aspect of aneurysms.
- Where this ischaemia occurs there is loss of the normal elastic nature of the media, allowing it to expand.
- Arachnodactyly – abnormally long and thin fingers in comparison to the palm. Fingers may also be bent backwards at the MCP to 180’ in some cases.
- Joint hypermobility
- Scoliosis – lateral curvature of the spine
- Chest deformity
- High arched palate
- Dislocation of lens in the eye
- Patients are usually tall and thin, with long limbs
Heart valve defects
Pre-disposes to aneurysms
- There is weakening of the media layer of the aorta, leading to dilation. In these cases, the dilatation typically occurs in the ascending aorta. There may also be valve defects (e.g. aortic regurg) which complicate the issue.
- In Marfan’s Syndrome, the root of the aorta is typically affected
Treatment of Marfan’s
β-blocker therapy – has been proven to reduce the rate/risk of dilatation of the aorta
Monitoring of aortic dilatation –via X-Ray, Echo, MRI or CT can be useful in patients with known Marfan’s. Usually patients are followed up with yearly echo to assess the size of the aorta. In some cases, elective replacement of the ascending aorta may be recommended, to prevent dissection but has a mortality of 5-10%.
Avoidance of endurance sports / activities
In pregnancy – as both pregnancy and Marfan’s are risk factors for AA, then during pregnancy, the aorta is closely monitored by 6 weekly echo’s.
- If the aortic root >4cm, ceasarian section should be considered
- β – blocker therapy is safe to continue during pregnancy
- Generally good, although less than the general population.
- Surgical interventions have increased the average life-expectancy by 13 years