Definition: A localised abnormal dilatation of a blood vessel. This includes arteries, veins and the heart. For an artery to be aneursymal there must be a focal dilatation of 1.5 times it's normal diameter. Ectasia is the term used for a general dilatation of more than 1.5 times.

True vs. False aneurysms: A true aneurysm involves all three layers of the blood vessel wall. Whereas a false aneurysm consists of clot which has leaked from the true lumen and is surrounded by connective tissue. Femoral artery puncture, e.g. for angiography, is a common cause of false aneurysms.

Fusiform aneurysms are the most common morphology

Pathology of aneurysms

• Degenerative: The idea of atherosclerosis causing AAA has been revised to a model that suggests degeneration due to an inflammatory process, leading to dilatation and subsequent plaque deposition. (Goldstone 1998)
• Infection: Classically syphilis. Septic embolisation (mycotic). Most studies report Staph. Aureus and Salmonella as the infective organisms.
• Collagen diseases: Marfan’s syndrome / Ehlers-Danlos syndrome (esp. Type IV)
• Congenital: Berry aneurysms present on the circle Willis.
• Traumatic: blunt and sharp trauma
• Iatrogenic e.g. after femoral artery puncture for angiograms

Abdominal Aortic Aneurysms

• Infra-renal aorta is commonest site of aortic aneurysm.
• Remember most are asymptomatic. Over 50% will die of other causes with their AAA intact.
• Affects 7% males and 2% females aged >65 and incidence is on the rise in the West.
• Strong FHx. 20% males with AAA will have a first degree relative with a AAA.
• Supra-renal extension occurs in 2-5%
• Often found incidentally. Esp. USS for prostatism.
• High association with aneurysms in other areas. Especially iliac and popliteal.
• Main complication is rupture (cf. dissection which results from a intimal tear resulting in blood tracking down the vessel wall splitting the media.)
• The annual rupture rate in the UK Small Aneurysm Trial (N = 2257, with about half in randomized arm and half in the registry) was 2.2% per year for the first 3 years of follow-up (Powell, 2001). The initial aneurysm diameter was 3-6 cm, and the mean was approximately 4.4 cm.

Investigation

CT slice of AAA at level of renal vein

• Examination
• B-Mode USS
• CT
• MRA - Often not useful for AAA as only shows the lumen where there is blood flow.
• AXR - remember to look for a rim of calcification

Treatment

• Avoid emergency by treating electively.
• Remember most patients are asymptomatic and operation carries reasonably high morbidity / mortality (2 - 5%).
• Trials have shown two quantative measures.
• Size ³ 5.5cm (UK) - 5cm USA
• Increase in size ³ 0.5cm in 12 months
• The UK Small Aneurysm Trial (1998) randomised just over 1000 patients with small (4 - 5.5 cm) aneurysms. There was no overall improvement in mortality in patients offered early surgery.
• Cronenwett (J Vasc Surg 1990) suggested that COPD and HT increased risk of rupture and should be taken into account.
• Overall 30 day mortality is ~ 5% (50% from IHD)

Emergency Treatment

• Presentation can be with a variety of abdo pain radiating to back and groin. So always suspect in men aged >55 with renal colic.
• Basic resuscitation - A B C
• Insert at least two large-bore cannulae and start an IVI
• Insert a urinary catheter
• Analgesia
• Cross match 6 units of blood
• Take straight to theatre. Does NOT need investigating with USS / CT first!!
• If systolic >100mmHg consider lowering BP with GTN etc