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78 Chapter 2: Cardiovascular system

Table 2.12 Types of aneurysm
Aetiology Site Cause Incidence
Atherosclerotic Abdominal and thoracic aorta Thinning and fibrous replacement Most common
of media
Syphilitic Ascending aorta and arch Inflammatory destruction of media Now rare
and fibrous replacement
Berry Cerebral arteries Congenital defects in elastic Common in patients with adult
lamina/media polycystic kidney disease
Infective (mycotic) Any Destruction of wall by bacteria in Rare
infected thrombus

Abdominal aortic aneurysm aneurysms, e.g. femoral and popliteal. Suprarenal
aneurysms may also involve the thoracic aorta.
Definition
As the aneurysms slowly enlarge at an average of 0.5
Abnormal dilation of the abdominal aorta.
cm per year, they cause local pressure problems and have
an increased risk of rupture. They may dissect and cut
Incidence off blood supply to tissue (e.g. kidneys) or rupture with
Abdominal aortic aneurysms (AAA) are present in 2% resulting haemorrhage.
of men aged 60–84 years and are an important cause of Altered flow patterns predispose to thrombus forma-
death, 6000 per annum in United Kingdom. tion, which may embolise to distal arteries or cause oc-
clusion at the site of the aneurysm.

Age
Clinical features
Increases with age, rare under 50 years.
Abdominal aortic aneurysms may be found incidentally
as a central expansile mass on examination or as calcifi-
Sex cation on an X-ray. A tender mass suggests a high risk of
M > F (10–20:1) rupture.
Patients may present with a dull, aching chronic or
intermittent epigastric or back pain due to expansion.
Geography
Rupture causes a tearing epigastric pain that radiates
Becoming more common in the developed world.
through to the back or referred sciatic or loin to groin
pain. Rupture through all three layers of the wall causes
Aetiology profound shock. Occasionally a small leak ‘herald bleed’
Riskfactorsareasforatherosclerosis,includingsmoking, maycauseashorter,lesssevereepisodeofpainsomedays
hypercholesterolaemia, age, sex, diabetes. Hypertension or weeks before rupture occurs.
in particular plays an important role in the enlargement Fistula formation into the bowel causes catastrophic
and rupture. Patients with abdominal aortic aneurysms fresh rectal bleeding.
commonly have associated coronary artery disease, cere-
brovascular disease and more extensive peripheral vas- Complications
cular disease. Thirty per cent of aneurysms will eventually rupture.
More than half of aneurysms over 6 cm will rupture
Pathophysiology within 2 years – thromboembolism.
The arterial wall becomes thinned and is replaced with
fibrous tissue and stretches to form a dilated saccular or Investigations
fusiform aneurysm. The majority (95%) are infrarenal, CT with contrast and ultrasound scans will demon-
i.e. arise below the renal arteries, but they may extend strate the position and wall thickness of the aneurysm.
down to the iliacs or there may be multiple separate Angiography or 3-D MRI reconstruction may be used to