Definitions
An aneurysm is a permanent localized dilatation of an artery to the extent that the affected artery is 1.5 times its normal diameter. A pseudo or false aneurysm is an expanding pulsating haematoma in continuity with a vessel lumen. It does not have an epithelial lining.
Key Points
- Screening for AAA by ultrasound in men aged 65–79 years results in a significant reduction in mortality from AAA. No benefit from screening in women or younger men.
- All patients with other vascular disease should be examined for AAA.
- There is no medical treatment for AAA but small aneurysms may be safely managed by surveillance and regular monitoring with intervention at ≥5.5 cm.
- Mortality for elective surgery is reduced by careful patient evaluation for hidden coronary or pulmonary disease.
- Beware of the diagnosis of left renal colic in the elderly.
Sites
Abdominal aorta, iliac, femoral and popliteal arteries. Cerebral and thoracic aneurysms (TAA) are less common.
Aetiology
- Atherosclerosis.
- Familial (abnormal collagenase or elastase activity).
- Congenital (cerebral (berry) aneurysm).
- Bacterial aortitis (mycotic aneurysm).
- Syphilitic aortitis (thoracic aneurysm).
Risk Factors
- Cigarette smoking.
- Hypertension.
- Hyperlipidaemia.
- Marfan syndrome and Ehlers – Danlos syndrome for TAA.
- Trauma for pseudoaneurysm, e.g. arterial puncture.
Pathology
- Aneurysms increase in size in line with the law of Laplace (T = RP), T = tension on the arterial wall, R = radius of artery, P = blood pressure. Increasing tension leads to rupture.
- Thrombus from within an aneurysm may be a source of peripheral emboli.
- Popliteal aneurysms may undergo complete thrombosis leading to acute leg ischaemia.
- Aneurysms may be fusiform (AAA, popliteal) or saccular (thoracic, cerebral).
- Acute aortic dissection (i.e.tear of the intima with blood tracking between the intima and media producing a second lumen) may occur with TAA.
Clinical Features of AAA
Asymptomatic
The vast majority have no symptoms and are found incidentally. This has led to the description of an AAA as ‘a U-boat in the belly’ and the development of screening programmes. Most TAAs are also asymptomatic and discovered on CXR.
Symptomatic AAA
- Back pain from pressure on the vertebral column.
- Rapid expansion causes flank or back pain.
- Rupture causes collapse, back pain and an ill-defined mass.
- Erosion into IVC causes CCF, loud abdominal bruit (machinery murmur), lower limb ischaemia and gross oedema.
Symptomatic TAA
- Pain: ascending aorta – chest pain; aortic arch – neck pain; descending aorta – back pain. Pain may be chronic from pressure or acute implying impending rupture.
- Most patients are hypertensive.
- Hoarseness, SVC obstruction, dysphagia, stridor and acute aortic valve incompetence may all occur.
Investigations
Detection of AAA
- Physical examination: not accurate.
- Plain abdominal X-ray: aortic calcification.
- Ultrasonography: best way of detecting and measuring aneurysm size – many localities have effective U/S-based screening services to reduce acute presentations of rupture.
- CT or MR angiography scan: provides good information regarding relationship between AAA, renal and iliac arteries.
- Angiography: needed for anatomical detail for planning endovascular repair.
Detection of TAA
- CXR and CT or MR angiography.
Determination of Fitness for Surgery
- History and examination.
- ECG ± stress testing.
- Radionuclide cardiac scanning (MUGA or stress thallium scan).
- Pulmonary function tests.
- U+E and creatinine for renal assessment.
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