An aneurysm is an abnormal focal arterial dilation. They are classified into true and false aneurysms (pseudo-aneurysm). True aneurysms involve all three layers of the arterial wall. A false aneurysm is a collection of blood which has leaked out of the artery but is then confined next to the vessel by surrounding tissue.
An aneurysm may be defined as a localized abnormal dilation of a blood vessel or the heart . It can arise anywhere in the body with varying presentations. Aneurysms can be both congenital and acquired. They can be classified on the basis of shape and size of the dilation into 2 main types.
Aneurysms have many causes. They can be due to congenital diseases, particularly those that damage the connective tissue, such as Marfan syndrome, Ehlers Danlos syndrome or Loeys-Dietz syndrome. Tilson et al described the potential for an autoimmune basis for the development of abdominal aortic aneurysms (AAA) involving the DRB1 major histocompatibility locus .
Conditions causing a disbalance in synthesis and degradation of collagen, such as increased matrix metalloproteinase (MMP) production by macrophages, decreased tissue inhibitor of metalloproteinase (TIMP) expression also contribute to aneurysm formation. Lastly, factors based on lifestyle such as hypertension, obesity, atherosclerosis, and high cholesterol, may also lead to the development of aneurysms. Indeed, hypertension and atherosclerosis are the two most important predisposing factors to aneurysms.
The incidence of aneurysms varies depending upon the type and gender. For example, AAA occur 8.2% in males in the UK but females only have an incidence of 0.6-1.4%.
In males the peak age of aneurysms is 80 years but the incidence peaks from 50 years of age. Females have a slightly delayed onset, with incidence rising sharply after the 6th decade of life.
Aneurysms are more common in males, with an approximate ratio of 2:1. However, the risk of rupture of large aneurysms (≥5.0 cm) is significantly greater in women than men (18 versus 12 percent) .
Aneurysms are much more common in Caucasians than people belonging to African-American and other races.
Aneurysms develop due to damage to vessel walls either due to factors acting directly on the vessel walls and weakening them, such as atherosclerotic plaques, nonenzymatic glycosylation of vessels in diabetes mellitus, and hypertension, or due to congenital defects in connective tissue structure and formation. Ischemia also contributes to the pathogenesis. Some common aneurysms are described below:
The United States National Lung, Heart and Blood Institute supported a research program that identified the following as mechanisms important in the development of AAA : Proteolytic degradation of aortic wall connective tissue which is followed by inflammation and immune responses. Two other factors include biochemical stress and molecular genetics.
Thoracic aortic aneurysms are most commonly associated with hypertension, although other causes such as Marfan syndrome and Loeys-Dietz syndrome are increasingly recognized . They may encroach on mediastinal structures leading to respiratory distress, difficulty in swallowing due to compression of esophagus, cough and hoarseness of voice due to irritation of recurrent laryngeal nerves, and sometimes secondary cardiac disease.
It has been suggested that patients with untreated large ascending or descending thoracic aneurysms are more likely to die of complications associated with their aneurysms than from any other cause . Re-rupture, particularly in subarachnoid hemorrhage (SAH) associated with cerebral aneurysm (CA), is associated with a mortality that is estimated to be 70 percent and aneurysm repair is the only effective treatment to prevent this occurrence . Overall, aneurysm is a progressive condition with mortality rates directly proportional to size of the dilation.
Presentation varies with the type of aneurysm involved. Most patients with AAA are asymptomatic but come to medical attention by finding of a pulsatile mass on physical examination, as the result of other abdominal imaging studies, or through ultrasound screening programs for AAA . Patients suffering from cerebral aneurysms may present with headache, nosebleed, visual symptoms, facial pain, altered levels of consciousness which may or may not be accompanied with seizures and autonomic disturbances.
Imaging studies include angiography, CT scan, MRI, Doppler ultrasound and echocardiography. For cerebral aneurysm, imaging tests like transcranial doppler ulrasonography, lumbar puncture and cervical spine imaging may be conducted.
On the basis of tests and imaging studies, the site of the aneurysm may be localized and often, the underlying cause may also be identified.
Medication include the use of calcium channel blockers, anticonvulsants if needed, and beta blockers. At least one clinical study showed that people who took beta blockers had a slower rate of growth of their AAA compared with people who took a placebo (0.36 versus 0.68 cm per year) .
Surgical intervention includes insertion of a surgical clip in the neck of the aneurysm. Endovascular coiling of the aneurysm can also be performed, often yielding better results.
Control and limiting of predisposing factors such as obesity and hypertension are of prime importance in preventive therapy. Particular care should be taken by diabetic patients to keep both blood sugar levels and cholesterol levels in normal limits.
An aneurysm is defined as a segmental, full-thickness dilation of a blood vessel 50 percent greater than its normal diameter .
They can be present from birth or develop later in life due to various reasons such as hypertension, obesity, high cholesterol, diabetes and weakening of vessel wall due to old age.
Signs and symptoms
Most aneurysms are asymptomatic, coming to notice usually during routine examinations. Rupture of an aneurysm, however, is a medical emergency and presents as sharp pain and subsequent collapse. Cerebral aneurysms may preset with symptoms of headache, visual disturbances, seizures and facial pain.
Treatment is supportive unless there is a high chance of rupture, in which case surgical intervention is imperative.