An aneurysm is a bulge in a blood vessel, usually an artery, due to a weakness in the vessel wall, particularly in the elastic, muscular, middle layer of the artery wall. An artery has three layers: the intima, which is the smooth inner layer; the media, or middle, layer; and the adventitia, which is the tough outer layer.

A true aneurysm involves all three layers, whereas a false aneurysm is a disruption or clot in one or two of the layers, causing a bulge in the vessel. A dissecting aneurysm occurs when blood separates the layers, thereby creating an extra channel, sometimes extending the full length of the artery, through which blood flow is diverted from the organs or tissues served by the blood vessel. This dangerous condition can develop in just hours or days.

The main danger of most untreated aneurysms is that they may rupture, or dissect, causing death from blood loss. Even if death does not occur, the failure of blood to reach vital organs can cause them to fail.

Causes

There are various causes of aneurysms. Those occurring in the arteries of the brain are often due to an inherited defect -- a weakness or lack of elastic tissue in the media. If an aneurysm in the brain ruptures, a stroke can result. Aneurysms in the small arteries may be caused by infections that weaken the vessel wall. Penetrating wounds can occasionally cause aneurysms.

The sexually transmitted disease syphilis may also cause aneurysms. Syphilis can cause vasculitis (inflammation of the smaller arteries that nourish a large one). When this occurs, these small arteries are lost, thereby denying nourishment to parts of the large arterial wall and causing scarring and death of tissue. This leads to weakness of the wall and formation of an aneurysm.

Dissecting aneurysms usually occur in the aorta. Atherosclerosis (hardening of the arteries) is the most common cause, especially in the elderly. If a young person is affected, the condition is usually caused by an inherited defect.

Symptoms

Symptoms of dissecting aneurysms of the aorta, if in the chest, include sudden, severe pain in the area of the aneurysm, often resembling a heart attack. There may be pain under the breastbone or in the back of the neck, difficulty in swallowing, shortness of breath, hoarseness, or a heavy cough.

An aneurysm in a neck artery may create a pulsating, swishing sound that the patient can detect.
Evidence of an aneurysm can be a tender, pulsating mass in the abdomen or a painful, tender mass at the back of the knee (the latter can lead to blood clots that can travel downward and result in death of tissue in the toes).

Symptoms of a dissecting aneurysm in the abdomen can include sudden, severe central or low abdominal pain radiating to the back; a loss of blood flow to the legs; and shock (collapse of circulation, signaled by fainting, pale and clammy skin, and rapid, weak pulse). Death can result quickly.

Diagnosis

Computed tomography (CT) and ultrasound studies of the affected areas are used to locate aneurysms and determine their extent. The most reliable and definitive test is an angiogram (also called an arteriogram). In this procedure, a thin catheter is inserted into an artery in the arm or leg and advanced to the site to be studied; a special dye is then injected through the catheter to outline the area so X-rays can be taken.

Treatment

Treatment of most aneurysms, especially dissecting aneurysms, should begin as soon as possible. Patients with dissecting aneurysms belong in an intensive care unit. Drugs are given to lower high blood pressure (which worsens a dissecting aneurysm) and thus reduce the chances of rupture. Occasionally, a dissecting aneurysm heals itself if pressure is lessened. Long-term medication that keeps blood pressure low is standard treatment for those who cannot undergo surgery.

Surgery, however, is by far the most satisfactory solution when it is possible. The damaged portion of the blood vessel is removed and replaced with a synthetic vessel or a natural vessel taken from elsewhere in the body. Patients with ruptured aortic aneurysms need emergency surgery, as do most patients with dissecting aneurysms. Rapid replacement of blood is necessary, as is intensive monitoring.

Surgery for aneurysm repair is usually long and difficult. However, with newer methods of diagnosis, many more people are being spared the risks of surgery by correction of the aneurysm before it becomes a life-threatening problem.